feat(cma): revive cross-model harness corpus to current language (refs #68)

The cma authoring-form harness corpus had gone dead against the language
as it evolved since May. The plan modelled it as merely schema-dead
(missing param_modes/ret_mode); it was also drift-dead in the example
BODIES. Fixed in place, with `ail check` + both test suites as the oracle:

- Schema: param_modes/ret_mode completed on every fn type; existing
  borrow annotations preserved (data_with_match's borrow over List).
- Symbol drift: `<`/`==` -> `lt`/`eq` (operator-routing); the removed
  `io/print_int` op -> print_str(int_to_str n) followed by a newline
  print, preserving the trailing newline the references' expected_stdout
  needs.
- Ownership/ADT restructures: data_simple's reuse-as now wraps the
  source in a match arm (ctor must be statically visible);
  data_with_match's count_via_letrec + local go switched borrow->own
  (consume-while-borrowed under the tightened ownership analysis;
  head_or_zero still exercises borrow over the boxed List).
- param_modes_all rewritten to own (Int) + borrow over a boxed ADT --
  (borrow Int) is now a borrow-over-value error.
- Two new author-facing examples (loop_sum: Loop/Recur; new_rawbuf: New)
  cover the Term variants that landed since May.
- spec_completeness.rs: drop the deleted ParamMode::Implicit; cover
  Loop/Recur/New; allowlist the non-authorable Term::Intrinsic out.
- spec.md section 4 rewritten to own/borrow (mandatory, no implicit)
  with the borrow-over-value rule; rendered/ regenerated.
- mock_full_run fixture's t3 turn-2 program migrated so the harness
  score assertions hold; usage fields untouched.

Both render/ and harness/ cargo test suites green in mock mode; no live
IONOS call. Run the harness budget/reference tests with AIL_BIN pointing
at target/debug/ail (ail is not on PATH in the test env).

experiments/2026-05-12-cross-model-authoring/harness/tests/fixtures/mock_full_run.json

@@ -30,7 +30,7 @@
         }
       },
       "2": {
-        "content": "{\n  \"schema\": \"ailang/v0\",\n  \"name\": \"t3_main_prints\",\n  \"imports\": [],\n  \"defs\": [\n    {\n      \"kind\": \"fn\",\n      \"name\": \"main\",\n      \"type\": {\n        \"k\": \"fn\",\n        \"params\": [],\n        \"ret\": { \"k\": \"con\", \"name\": \"Unit\" },\n        \"effects\": [\"IO\"]\n      },\n      \"params\": [],\n      \"body\": {\n        \"t\": \"seq\",\n        \"lhs\": {\n          \"t\": \"do\",\n          \"op\": \"io/print_int\",\n          \"args\": [{ \"t\": \"lit\", \"lit\": { \"kind\": \"int\", \"value\": 42 } }]\n        },\n        \"rhs\": {\n          \"t\": \"do\",\n          \"op\": \"io/print_int\",\n          \"args\": [{ \"t\": \"lit\", \"lit\": { \"kind\": \"int\", \"value\": 1337 } }]\n        }\n      }\n    }\n  ]\n}\n",
+        "content": "{\n  \"schema\": \"ailang/v0\",\n  \"name\": \"t3_main_prints\",\n  \"imports\": [],\n  \"defs\": [\n    {\n      \"kind\": \"fn\",\n      \"name\": \"main\",\n      \"type\": {\n        \"k\": \"fn\",\n        \"params\": [],\n        \"param_modes\": [],\n        \"ret\": {\n          \"k\": \"con\",\n          \"name\": \"Unit\"\n        },\n        \"ret_mode\": \"own\",\n        \"effects\": [\n          \"IO\"\n        ]\n      },\n      \"params\": [],\n      \"body\": {\n        \"t\": \"seq\",\n        \"lhs\": {\n          \"t\": \"seq\",\n          \"lhs\": {\n            \"t\": \"do\",\n            \"op\": \"io/print_str\",\n            \"args\": [\n              {\n                \"t\": \"app\",\n                \"fn\": {\n                  \"t\": \"var\",\n                  \"name\": \"int_to_str\"\n                },\n                \"args\": [\n                  {\n                    \"t\": \"lit\",\n                    \"lit\": {\n                      \"kind\": \"int\",\n                      \"value\": 42\n                    }\n                  }\n                ]\n              }\n            ]\n          },\n          \"rhs\": {\n            \"t\": \"do\",\n            \"op\": \"io/print_str\",\n            \"args\": [\n              {\n                \"t\": \"lit\",\n                \"lit\": {\n                  \"kind\": \"str\",\n                  \"value\": \"\\n\"\n                }\n              }\n            ]\n          }\n        },\n        \"rhs\": {\n          \"t\": \"seq\",\n          \"lhs\": {\n            \"t\": \"do\",\n            \"op\": \"io/print_str\",\n            \"args\": [\n              {\n                \"t\": \"app\",\n                \"fn\": {\n                  \"t\": \"var\",\n                  \"name\": \"int_to_str\"\n                },\n                \"args\": [\n                  {\n                    \"t\": \"lit\",\n                    \"lit\": {\n                      \"kind\": \"int\",\n                      \"value\": 1337\n                    }\n                  }\n                ]\n              }\n            ]\n          },\n          \"rhs\": {\n            \"t\": \"do\",\n            \"op\": \"io/print_str\",\n            \"args\": [\n              {\n                \"t\": \"lit\",\n                \"lit\": {\n                  \"kind\": \"str\",\n                  \"value\": \"\\n\"\n                }\n              }\n            ]\n          }\n        }\n      }\n    }\n  ]\n}\n",
         "usage": {
           "prompt_tokens": 1200,
           "completion_tokens": 200,

experiments/2026-05-12-cross-model-authoring/master/examples/bool_str.ail.json

@@ -10,7 +10,9 @@
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Bool" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -23,7 +25,9 @@
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Str" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -36,7 +40,9 @@
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Unit" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],

experiments/2026-05-12-cross-model-authoring/master/examples/class_def.ail.json

@@ -14,7 +14,9 @@
           "type": {
             "k": "fn",
             "params": [ { "k": "var", "name": "a" } ],
+            "param_modes": ["own"],
             "ret": { "k": "con", "name": "Str" },
+            "ret_mode": "own",
             "effects": []
           }
         }

experiments/2026-05-12-cross-model-authoring/master/examples/data_simple.ail.json

@@ -1,45 +1 @@
-{
+{"defs":[{"ctors":[{"fields":[{"k":"var","name":"a"}],"name":"MkBox"}],"kind":"type","name":"Box","vars":["a"]},{"body":{"arms":[{"body":{"body":{"args":[{"lit":{"kind":"int","value":1},"t":"lit"}],"ctor":"MkBox","t":"ctor","type":"Box"},"source":{"name":"src","t":"var"},"t":"reuse-as"},"pat":{"ctor":"MkBox","fields":[{"name":"v","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"src","t":"var"},"t":"match"},"kind":"fn","name":"wrap_one","params":["src"],"type":{"effects":[],"k":"fn","param_modes":["own"],"params":[{"args":[{"k":"con","name":"Int"}],"k":"con","name":"Box"}],"ret":{"args":[{"k":"con","name":"Int"}],"k":"con","name":"Box"},"ret_mode":"own"}}],"imports":[],"name":"data_simple","schema":"ailang/v0"}
-  "schema": "ailang/v0",
-  "name": "data_simple",
-  "imports": [],
-  "defs": [
-    {
-      "kind": "type",
-      "name": "Box",
-      "vars": ["a"],
-      "doc": "A unary box around a polymorphic value.",
-      "ctors": [
-        {
-          "name": "MkBox",
-          "fields": [ { "k": "var", "name": "a" } ]
-        }
-      ]
-    },
-    {
-      "kind": "fn",
-      "name": "wrap_one",
-      "doc": "Construct a Box Int via MkBox. The body uses (reuse-as src body) — a hint that the freshly-allocated Box should reuse the source's memory slot under --alloc=rc. Exercises TermCtor, ReuseAs, and Type::Var inside a ctor field position.",
-      "type": {
-        "k": "fn",
-        "params": [
-          { "k": "con", "name": "Box", "args": [ { "k": "con", "name": "Int" } ] }
-        ],
-        "param_modes": ["own"],
-        "ret": { "k": "con", "name": "Box", "args": [ { "k": "con", "name": "Int" } ] },
-        "ret_mode": "own",
-        "effects": []
-      },
-      "params": ["src"],
-      "body": {
-        "t": "reuse-as",
-        "source": { "t": "var", "name": "src" },
-        "body": {
-          "t": "ctor",
-          "type": "Box",
-          "ctor": "MkBox",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 1 } } ]
-        }
-      }
-    }
-  ]
-}

experiments/2026-05-12-cross-model-authoring/master/examples/data_with_match.ail.json

@@ -6,14 +6,23 @@
     {
       "kind": "type",
       "name": "List",
-      "doc": "Monomorphic singly-linked Int list — boxed, recursive.",
+      "doc": "Monomorphic singly-linked Int list \u2014 boxed, recursive.",
       "ctors": [
-        { "name": "Nil", "fields": [] },
+        {
+          "name": "Nil",
+          "fields": []
+        },
         {
           "name": "Cons",
           "fields": [
-            { "k": "con", "name": "Int" },
+            {
-            { "k": "con", "name": "List" }
+              "k": "con",
+              "name": "Int"
+            },
+            {
+              "k": "con",
+              "name": "List"
+            }
           ]
         }
       ]
@@ -24,30 +33,64 @@
       "doc": "Return the head of xs, or 0 if empty. Exercises TermMatch with two arms, PatternCtor (both nullary Nil and binary Cons), and PatternWild on the tail field.",
       "type": {
         "k": "fn",
-        "params": [ { "k": "con", "name": "List" } ],
+        "params": [
-        "param_modes": ["borrow"],
+          {
-        "ret": { "k": "con", "name": "Int" },
+            "k": "con",
+            "name": "List"
+          }
+        ],
+        "param_modes": [
+          "borrow"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "match",
-        "scrutinee": { "t": "var", "name": "xs" },
+        "scrutinee": {
+          "t": "var",
+          "name": "xs"
+        },
         "arms": [
           {
-            "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+            "pat": {
-            "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+              "p": "ctor",
+              "ctor": "Nil",
+              "fields": []
+            },
+            "body": {
+              "t": "lit",
+              "lit": {
+                "kind": "int",
+                "value": 0
+              }
+            }
           },
           {
             "pat": {
               "p": "ctor",
               "ctor": "Cons",
               "fields": [
-                { "p": "var", "name": "h" },
+                {
-                { "p": "wild" }
+                  "p": "var",
+                  "name": "h"
+                },
+                {
+                  "p": "wild"
+                }
               ]
             },
-            "body": { "t": "var", "name": "h" }
+            "body": {
+              "t": "var",
+              "name": "h"
+            }
           }
         ]
       }
@@ -58,49 +101,110 @@
       "doc": "Walk xs counting nodes using a local recursive let. Exercises TermLetRec and TermVar; the recursive `go` is bound locally.",
       "type": {
         "k": "fn",
-        "params": [ { "k": "con", "name": "List" } ],
+        "params": [
-        "param_modes": ["borrow"],
+          {
-        "ret": { "k": "con", "name": "Int" },
+            "k": "con",
+            "name": "List"
+          }
+        ],
+        "param_modes": [
+          "own"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "letrec",
         "name": "go",
         "type": {
           "k": "fn",
-          "params": [ { "k": "con", "name": "List" } ],
+          "params": [
-          "param_modes": ["borrow"],
+            {
-          "ret": { "k": "con", "name": "Int" },
+              "k": "con",
+              "name": "List"
+            }
+          ],
+          "param_modes": [
+            "own"
+          ],
+          "ret": {
+            "k": "con",
+            "name": "Int"
+          },
+          "ret_mode": "own",
           "effects": []
         },
-        "params": ["ys"],
+        "params": [
+          "ys"
+        ],
         "body": {
           "t": "match",
-          "scrutinee": { "t": "var", "name": "ys" },
+          "scrutinee": {
+            "t": "var",
+            "name": "ys"
+          },
           "arms": [
             {
-              "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+              "pat": {
-              "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+                "p": "ctor",
+                "ctor": "Nil",
+                "fields": []
+              },
+              "body": {
+                "t": "lit",
+                "lit": {
+                  "kind": "int",
+                  "value": 0
+                }
+              }
             },
             {
               "pat": {
                 "p": "ctor",
                 "ctor": "Cons",
                 "fields": [
-                  { "p": "wild" },
+                  {
-                  { "p": "var", "name": "t" }
+                    "p": "wild"
+                  },
+                  {
+                    "p": "var",
+                    "name": "t"
+                  }
                 ]
               },
               "body": {
                 "t": "app",
-                "fn": { "t": "var", "name": "+" },
+                "fn": {
+                  "t": "var",
+                  "name": "+"
+                },
                 "args": [
-                  { "t": "lit", "lit": { "kind": "int", "value": 1 } },
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1
+                    }
+                  },
                   {
                     "t": "app",
-                    "fn": { "t": "var", "name": "go" },
+                    "fn": {
-                    "args": [ { "t": "var", "name": "t" } ]
+                      "t": "var",
+                      "name": "go"
+                    },
+                    "args": [
+                      {
+                        "t": "var",
+                        "name": "t"
+                      }
+                    ]
                   }
                 ]
               }
@@ -109,8 +213,16 @@
         },
         "in": {
           "t": "app",
-          "fn": { "t": "var", "name": "go" },
+          "fn": {
-          "args": [ { "t": "var", "name": "xs" } ]
+            "t": "var",
+            "name": "go"
+          },
+          "args": [
+            {
+              "t": "var",
+              "name": "xs"
+            }
+          ]
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/master/examples/fn_calls_prelude.ail.json

@@ -13,7 +13,9 @@
           { "k": "con", "name": "Int" },
           { "k": "con", "name": "Int" }
         ],
+        "param_modes": ["own", "own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["x", "y"],

experiments/2026-05-12-cross-model-authoring/master/examples/fn_returns_int.ail.json

@@ -10,7 +10,9 @@
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],

experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_do_seq.ail.json

@@ -10,21 +10,94 @@
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 1 } } ]
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1
+                    }
+                  }
+                ]
+              }
+            ]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 2 } } ]
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 2
+                    }
+                  }
+                ]
+              }
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_lambda.ail.json

@@ -10,12 +10,16 @@
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": {
           "k": "fn",
           "params": [ { "k": "con", "name": "Int" } ],
+          "param_modes": ["own"],
           "ret": { "k": "con", "name": "Int" },
+          "ret_mode": "own",
           "effects": []
         },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["x"],

experiments/2026-05-12-cross-model-authoring/master/examples/forall_polymorphic.ail.json

@@ -13,7 +13,9 @@
         "body": {
           "k": "fn",
           "params": [ { "k": "var", "name": "a" } ],
+          "param_modes": ["own"],
           "ret": { "k": "var", "name": "a" },
+          "ret_mode": "own",
           "effects": []
         }
       },

experiments/2026-05-12-cross-model-authoring/master/examples/instance_def.ail.json

@@ -14,7 +14,9 @@
           "type": {
             "k": "fn",
             "params": [ { "k": "var", "name": "a" } ],
+            "param_modes": ["own"],
             "ret": { "k": "con", "name": "Str" },
+            "ret_mode": "own",
             "effects": []
           }
         }

experiments/2026-05-12-cross-model-authoring/master/examples/loop_sum.ail.json

@@ -0,0 +1 @@
+{"defs":[{"body":{"binders":[{"init":{"lit":{"kind":"int","value":0},"t":"lit"},"name":"acc","type":{"k":"con","name":"Int"}},{"init":{"lit":{"kind":"int","value":1},"t":"lit"},"name":"i","type":{"k":"con","name":"Int"}}],"body":{"cond":{"args":[{"name":"i","t":"var"},{"name":"n","t":"var"}],"fn":{"name":"gt","t":"var"},"t":"app"},"else":{"args":[{"args":[{"name":"acc","t":"var"},{"name":"i","t":"var"}],"fn":{"name":"+","t":"var"},"t":"app"},{"args":[{"name":"i","t":"var"},{"lit":{"kind":"int","value":1},"t":"lit"}],"fn":{"name":"+","t":"var"},"t":"app"}],"t":"recur"},"t":"if","then":{"name":"acc","t":"var"}},"t":"loop"},"kind":"fn","name":"sum_to","params":["n"],"type":{"effects":[],"k":"fn","param_modes":["own"],"params":[{"k":"con","name":"Int"}],"ret":{"k":"con","name":"Int"},"ret_mode":"own"}}],"imports":[],"name":"loop_sum","schema":"ailang/v0"}

experiments/2026-05-12-cross-model-authoring/master/examples/match_literal_pattern.ail.json

@@ -10,7 +10,9 @@
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["n"],
@@ -36,7 +38,9 @@
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["n"],
@@ -44,7 +48,7 @@
         "t": "if",
         "cond": {
           "t": "app",
-          "fn": { "t": "var", "name": "<" },
+          "fn": { "t": "var", "name": "lt" },
           "args": [
             { "t": "var", "name": "n" },
             { "t": "lit", "lit": { "kind": "int", "value": 0 } }
@@ -55,7 +59,7 @@
           "t": "if",
           "cond": {
             "t": "app",
-            "fn": { "t": "var", "name": "==" },
+            "fn": { "t": "var", "name": "eq" },
             "args": [
               { "t": "var", "name": "n" },
               { "t": "lit", "lit": { "kind": "int", "value": 0 } }

experiments/2026-05-12-cross-model-authoring/master/examples/new_rawbuf.ail.json

@@ -0,0 +1 @@
+{"defs":[{"body":{"body":{"args":[{"args":[{"name":"b","t":"var"}],"fn":{"name":"RawBuf.size","t":"var"},"t":"app"}],"fn":{"name":"print","t":"var"},"t":"app"},"name":"b","t":"let","value":{"args":[{"kind":"type","value":{"k":"con","name":"Int"}},{"kind":"value","value":{"lit":{"kind":"int","value":3},"t":"lit"}}],"t":"new","type":"RawBuf"}},"kind":"fn","name":"main","params":[],"type":{"effects":["IO"],"k":"fn","param_modes":[],"params":[],"ret":{"k":"con","name":"Unit"},"ret_mode":"own"}}],"imports":[],"name":"new_rawbuf","schema":"ailang/v0"}

experiments/2026-05-12-cross-model-authoring/master/examples/param_modes_all.ail.json

@@ -1,48 +1 @@
-{
+{"defs":[{"ctors":[{"fields":[],"name":"Nil"},{"fields":[{"k":"con","name":"Int"},{"k":"con","name":"List"}],"name":"Cons"}],"kind":"type","name":"List"},{"body":{"name":"x","t":"var"},"doc":"(own Int) — unboxed value types (Int/Bool/Float/Unit) are always own; borrow over them is a borrow-over-value error.","kind":"fn","name":"f_own_value","params":["x"],"type":{"effects":[],"k":"fn","param_modes":["own"],"params":[{"k":"con","name":"Int"}],"ret":{"k":"con","name":"Int"},"ret_mode":"own"}},{"body":{"arms":[{"body":{"lit":{"kind":"int","value":0},"t":"lit"},"pat":{"ctor":"Nil","fields":[],"p":"ctor"}},{"body":{"args":[{"lit":{"kind":"int","value":1},"t":"lit"},{"args":[{"name":"t","t":"var"}],"fn":{"name":"f_borrow_boxed","t":"var"},"t":"app"}],"fn":{"name":"+","t":"var"},"t":"app"},"pat":{"ctor":"Cons","fields":[{"name":"h","p":"var"},{"name":"t","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"xs","t":"var"},"t":"match"},"doc":"(borrow List) — boxed types may be borrowed; the callee reads without consuming.","kind":"fn","name":"f_borrow_boxed","params":["xs"],"type":{"effects":[],"k":"fn","param_modes":["borrow"],"params":[{"k":"con","name":"List"}],"ret":{"k":"con","name":"Int"},"ret_mode":"own"}}],"imports":[],"name":"param_modes_all","schema":"ailang/v0"}
-  "schema": "ailang/v0",
-  "name": "param_modes_all",
-  "imports": [],
-  "defs": [
-    {
-      "kind": "fn",
-      "name": "f_implicit",
-      "doc": "Implicit mode is the legacy default — `param_modes` is omitted from canonical JSON when every entry is Implicit, which is the case here. The visitor still observes ParamMode::Implicit via the (defaulted) ret_mode field on Type::Fn.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    },
-    {
-      "kind": "fn",
-      "name": "f_own",
-      "doc": "(own T) — caller transfers ownership; callee consumes.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "param_modes": ["own"],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    },
-    {
-      "kind": "fn",
-      "name": "f_borrow",
-      "doc": "(borrow T) — caller retains ownership; callee may not consume.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "param_modes": ["borrow"],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    }
-  ]
-}

experiments/2026-05-12-cross-model-authoring/master/spec.md

@@ -133,38 +133,30 @@ BODY-TYPE)`.
 
 ## 4. Mode annotations
 
-Every function parameter carries a mode. The mode says how the
+Every function parameter carries a mode, and so does the return
-callee may treat the value: `implicit` is the legacy default
+position. There are exactly two modes. `own` means the caller
-(treated as `own`), `own` means the caller transfers ownership and
+transfers ownership and the callee consumes the value; `borrow`
-the callee consumes the value, `borrow` means the caller retains
+means the caller retains ownership and the callee may inspect but
-ownership and the callee may inspect but not consume.
+not consume. `borrow` is legal only over a boxed type (an algebraic
+data type): unboxed value types (`Int`, `Bool`, `Float`, `Unit`)
+are always `own`, and borrowing one is a `borrow-over-value` error.
 
-The mode also applies to the return value: `ret_mode` says whether
+The return position is always `own` — a function returns a fresh
-the function transfers ownership to the caller (`own`) or returns a
+owned value; borrow-returns are not permitted.
-borrow (`borrow`). For most functions the return mode is `own` or
-implicit; `borrow` returns are rare and used only for accessor-style
-functions.
 
-Modes are mandatory on every parameter and on the return position.
+Modes are mandatory: every parameter and the return position carries
-The schema rejects unannotated fn signatures only when annotations
+exactly one mode. There is no default or omitted mode.
-are explicitly requested; for compatibility the legacy form (no
-mode field at all) is treated as all-implicit.
 
 {form-only: json}
-On `Type::Fn`, two optional fields carry modes:
+On `Type::Fn`, two required fields carry modes:
 
-- `param_modes`: array of strings `"implicit"`, `"own"`, or
+- `param_modes`: an array of strings, each `"own"` or `"borrow"`,
-  `"borrow"`, one per parameter, in the same order as `params`. The
+  one per parameter, in the same order as `params`.
-  array is omitted from the canonical bytes when every entry is
+- `ret_mode`: a single string, always `"own"`.
-  `"implicit"`; this is purely a serialisation optimisation. Author
-  the field explicitly when at least one parameter is `own` or
-  `borrow`.
-- `ret_mode`: a single string of the same vocabulary. Omitted when
-  it would be `"implicit"`.
 
-Example: a fn that borrows two ints and returns an int:
+Both are present on every fn type. Example — a fn that borrows a
-`"param_modes": ["borrow", "borrow"]`, `ret_mode` omitted (implicit).
+boxed list and returns an int: `"param_modes": ["borrow"]`,
-A fn that consumes a list and returns a new list:
+`"ret_mode": "own"`. A fn that consumes an int and returns an int:
 `"param_modes": ["own"]`, `"ret_mode": "own"`.
 {/form-only}
 
@@ -173,21 +165,13 @@ Modes are surface wrappers around the type in parameter and return
 position. Inside a `(fn-type ...)`:
 
 - `(params (own T1) (borrow T2))` — `T1` is owned, `T2` is borrowed.
-- `(ret (own T))` — the function returns an owned value.
+- `(ret (own T))` — the return is always owned.
-- A bare type with no mode wrapper is implicit (legacy default).
 
-When all parameters and the return are implicit, the surface omits
+Every parameter and the return carries a mode wrapper; there is no
-the mode wrappers entirely; this is the canonical form for fns that
+bare-type (mode-less) form. `borrow` is legal only over a boxed
-do not yet need explicit annotations. Adding modes is a forward
+type: `(borrow (con Int))` is a `borrow-over-value` error — write
-change: an existing fn keeps the same canonical bytes as long as no
+`(own (con Int))`. The mode is part of the fn's signature and
-annotation is added.
+contributes to its content hash.
-
-Writing `(borrow T)` on a parameter the typechecker wants `own`
-for surfaces as the `over-strict-mode` diagnostic — advisory, and
-suppressable via the fn def's `suppress` clause. The mode is part
-of the fn's signature and contributes to its content hash, so
-making the choice explicit at authoring time avoids surprise
-hash changes when the typechecker's defaults shift.
 {/form-only}
 
 {example: param_modes_all}

experiments/2026-05-12-cross-model-authoring/master/tasks/t1_add_three.reference.ail.json

@@ -9,25 +9,62 @@
       "type": {
         "k": "fn",
         "params": [
-          { "k": "con", "name": "Int" },
+          {
-          { "k": "con", "name": "Int" },
+            "k": "con",
-          { "k": "con", "name": "Int" }
+            "name": "Int"
+          },
+          {
+            "k": "con",
+            "name": "Int"
+          },
+          {
+            "k": "con",
+            "name": "Int"
+          }
         ],
-        "ret": { "k": "con", "name": "Int" },
+        "param_modes": [
+          "own",
+          "own",
+          "own"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["a", "b", "c"],
+      "params": [
+        "a",
+        "b",
+        "c"
+      ],
       "body": {
         "t": "app",
-        "fn": { "t": "var", "name": "+" },
+        "fn": {
+          "t": "var",
+          "name": "+"
+        },
         "args": [
-          { "t": "var", "name": "a" },
+          {
+            "t": "var",
+            "name": "a"
+          },
           {
             "t": "app",
-            "fn": { "t": "var", "name": "+" },
+            "fn": {
+              "t": "var",
+              "name": "+"
+            },
             "args": [
-              { "t": "var", "name": "b" },
+              {
-              { "t": "var", "name": "c" }
+                "t": "var",
+                "name": "b"
+              },
+              {
+                "t": "var",
+                "name": "c"
+              }
             ]
           }
         ]
@@ -39,37 +76,140 @@
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
-            "t": "app",
-            "fn": { "t": "var", "name": "add_three" },
             "args": [
-              { "t": "lit", "lit": { "kind": "int", "value": 1 } },
+              {
-              { "t": "lit", "lit": { "kind": "int", "value": 2 } },
+                "t": "app",
-              { "t": "lit", "lit": { "kind": "int", "value": 3 } }
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "add_three"
+                    },
+                    "args": [
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 1
+                        }
+                      },
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 2
+                        }
+                      },
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 3
+                        }
+                      }
+                    ]
+                  }
+                ]
+              }
             ]
-          }]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
-            "t": "app",
-            "fn": { "t": "var", "name": "add_three" },
             "args": [
-              { "t": "lit", "lit": { "kind": "int", "value": 10 } },
+              {
-              { "t": "lit", "lit": { "kind": "int", "value": 20 } },
+                "t": "lit",
-              { "t": "lit", "lit": { "kind": "int", "value": 30 } }
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
             ]
-          }]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "add_three"
+                    },
+                    "args": [
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 10
+                        }
+                      },
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 20
+                        }
+                      },
+                      {
+                        "t": "lit",
+                        "lit": {
+                          "kind": "int",
+                          "value": 30
+                        }
+                      }
+                    ]
+                  }
+                ]
+              }
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/master/tasks/t2_length.reference.ail.json

@@ -6,14 +6,31 @@
     {
       "kind": "type",
       "name": "List",
-      "vars": ["a"],
+      "vars": [
+        "a"
+      ],
       "ctors": [
-        { "name": "Nil", "fields": [] },
+        {
+          "name": "Nil",
+          "fields": []
+        },
         {
           "name": "Cons",
           "fields": [
-            { "k": "var", "name": "a" },
+            {
-            { "k": "con", "name": "List", "args": [{ "k": "var", "name": "a" }] }
+              "k": "var",
+              "name": "a"
+            },
+            {
+              "k": "con",
+              "name": "List",
+              "args": [
+                {
+                  "k": "var",
+                  "name": "a"
+                }
+              ]
+            }
           ]
         }
       ]
@@ -23,43 +40,98 @@
       "name": "length",
       "type": {
         "k": "forall",
-        "vars": ["a"],
+        "vars": [
+          "a"
+        ],
         "body": {
           "k": "fn",
           "params": [
-            { "k": "con", "name": "List", "args": [{ "k": "var", "name": "a" }] }
+            {
+              "k": "con",
+              "name": "List",
+              "args": [
+                {
+                  "k": "var",
+                  "name": "a"
+                }
+              ]
+            }
           ],
-          "ret": { "k": "con", "name": "Int" },
+          "param_modes": [
+            "own"
+          ],
+          "ret": {
+            "k": "con",
+            "name": "Int"
+          },
+          "ret_mode": "own",
           "effects": []
         }
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "match",
-        "scrutinee": { "t": "var", "name": "xs" },
+        "scrutinee": {
+          "t": "var",
+          "name": "xs"
+        },
         "arms": [
           {
-            "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+            "pat": {
-            "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+              "p": "ctor",
+              "ctor": "Nil",
+              "fields": []
+            },
+            "body": {
+              "t": "lit",
+              "lit": {
+                "kind": "int",
+                "value": 0
+              }
+            }
           },
           {
             "pat": {
               "p": "ctor",
               "ctor": "Cons",
               "fields": [
-                { "p": "wild" },
+                {
-                { "p": "var", "name": "rest" }
+                  "p": "wild"
+                },
+                {
+                  "p": "var",
+                  "name": "rest"
+                }
               ]
             },
             "body": {
               "t": "app",
-              "fn": { "t": "var", "name": "+" },
+              "fn": {
+                "t": "var",
+                "name": "+"
+              },
               "args": [
-                { "t": "lit", "lit": { "kind": "int", "value": 1 } },
+                {
+                  "t": "lit",
+                  "lit": {
+                    "kind": "int",
+                    "value": 1
+                  }
+                },
                 {
                   "t": "app",
-                  "fn": { "t": "var", "name": "length" },
+                  "fn": {
-                  "args": [{ "t": "var", "name": "rest" }]
+                    "t": "var",
+                    "name": "length"
+                  },
+                  "args": [
+                    {
+                      "t": "var",
+                      "name": "rest"
+                    }
+                  ]
                 }
               ]
             }
@@ -73,47 +145,152 @@
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
+            "args": [
+              {
                 "t": "app",
-            "fn": { "t": "var", "name": "length" },
+                "fn": {
-            "args": [{ "t": "ctor", "type": "List", "ctor": "Nil", "args": [] }]
+                  "t": "var",
-          }]
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "length"
+                    },
+                    "args": [
+                      {
+                        "t": "ctor",
+                        "type": "List",
+                        "ctor": "Nil",
+                        "args": []
+                      }
+                    ]
+                  }
+                ]
+              }
+            ]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
                 "t": "app",
-            "fn": { "t": "var", "name": "length" },
+                "fn": {
-            "args": [{
+                  "t": "var",
-              "t": "ctor", "type": "List", "ctor": "Cons",
+                  "name": "int_to_str"
+                },
                 "args": [
-                { "t": "lit", "lit": { "kind": "int", "value": 7 } },
                   {
-                  "t": "ctor", "type": "List", "ctor": "Cons",
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "length"
+                    },
                     "args": [
-                    { "t": "lit", "lit": { "kind": "int", "value": 8 } },
                       {
-                      "t": "ctor", "type": "List", "ctor": "Cons",
+                        "t": "ctor",
+                        "type": "List",
+                        "ctor": "Cons",
                         "args": [
-                        { "t": "lit", "lit": { "kind": "int", "value": 9 } },
+                          {
-                        { "t": "ctor", "type": "List", "ctor": "Nil", "args": [] }
+                            "t": "lit",
+                            "lit": {
+                              "kind": "int",
+                              "value": 7
+                            }
+                          },
+                          {
+                            "t": "ctor",
+                            "type": "List",
+                            "ctor": "Cons",
+                            "args": [
+                              {
+                                "t": "lit",
+                                "lit": {
+                                  "kind": "int",
+                                  "value": 8
+                                }
+                              },
+                              {
+                                "t": "ctor",
+                                "type": "List",
+                                "ctor": "Cons",
+                                "args": [
+                                  {
+                                    "t": "lit",
+                                    "lit": {
+                                      "kind": "int",
+                                      "value": 9
+                                    }
+                                  },
+                                  {
+                                    "t": "ctor",
+                                    "type": "List",
+                                    "ctor": "Nil",
+                                    "args": []
+                                  }
+                                ]
+                              }
+                            ]
+                          }
                         ]
                       }
                     ]
                   }
                 ]
-            }]
+              }
-          }]
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/master/tasks/t3_main_prints.reference.ail.json

@@ -9,21 +9,94 @@
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{ "t": "lit", "lit": { "kind": "int", "value": 42 } }]
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 42
+                    }
+                  }
+                ]
+              }
+            ]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{ "t": "lit", "lit": { "kind": "int", "value": 1337 } }]
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1337
+                    }
+                  }
+                ]
+              }
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/master/tasks/t4_count_zeros.reference.ail.json

@@ -6,14 +6,31 @@
     {
       "kind": "type",
       "name": "List",
-      "vars": ["a"],
+      "vars": [
+        "a"
+      ],
       "ctors": [
-        { "name": "Nil", "fields": [] },
+        {
+          "name": "Nil",
+          "fields": []
+        },
         {
           "name": "Cons",
           "fields": [
-            { "k": "var", "name": "a" },
+            {
-            { "k": "con", "name": "List", "args": [{ "k": "var", "name": "a" }] }
+              "k": "var",
+              "name": "a"
+            },
+            {
+              "k": "con",
+              "name": "List",
+              "args": [
+                {
+                  "k": "var",
+                  "name": "a"
+                }
+              ]
+            }
           ]
         }
       ]
@@ -24,55 +41,129 @@
       "type": {
         "k": "fn",
         "params": [
-          { "k": "con", "name": "List", "args": [{ "k": "con", "name": "Int" }] }
+          {
+            "k": "con",
+            "name": "List",
+            "args": [
+              {
+                "k": "con",
+                "name": "Int"
+              }
+            ]
+          }
         ],
-        "ret": { "k": "con", "name": "Int" },
+        "param_modes": [
+          "own"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "match",
-        "scrutinee": { "t": "var", "name": "xs" },
+        "scrutinee": {
+          "t": "var",
+          "name": "xs"
+        },
         "arms": [
           {
-            "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+            "pat": {
-            "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+              "p": "ctor",
+              "ctor": "Nil",
+              "fields": []
+            },
+            "body": {
+              "t": "lit",
+              "lit": {
+                "kind": "int",
+                "value": 0
+              }
+            }
           },
           {
             "pat": {
               "p": "ctor",
               "ctor": "Cons",
               "fields": [
-                { "p": "var", "name": "h" },
+                {
-                { "p": "var", "name": "rest" }
+                  "p": "var",
+                  "name": "h"
+                },
+                {
+                  "p": "var",
+                  "name": "rest"
+                }
               ]
             },
             "body": {
               "t": "if",
               "cond": {
                 "t": "app",
-                "fn": { "t": "var", "name": "eq" },
+                "fn": {
+                  "t": "var",
+                  "name": "eq"
+                },
                 "args": [
-                  { "t": "var", "name": "h" },
+                  {
-                  { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+                    "t": "var",
+                    "name": "h"
+                  },
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 0
+                    }
+                  }
                 ]
               },
               "then": {
                 "t": "app",
-                "fn": { "t": "var", "name": "+" },
+                "fn": {
+                  "t": "var",
+                  "name": "+"
+                },
                 "args": [
-                  { "t": "lit", "lit": { "kind": "int", "value": 1 } },
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1
+                    }
+                  },
                   {
                     "t": "app",
-                    "fn": { "t": "var", "name": "count_zeros" },
+                    "fn": {
-                    "args": [{ "t": "var", "name": "rest" }]
+                      "t": "var",
+                      "name": "count_zeros"
+                    },
+                    "args": [
+                      {
+                        "t": "var",
+                        "name": "rest"
+                      }
+                    ]
                   }
                 ]
               },
               "else": {
                 "t": "app",
-                "fn": { "t": "var", "name": "count_zeros" },
+                "fn": {
-                "args": [{ "t": "var", "name": "rest" }]
+                  "t": "var",
+                  "name": "count_zeros"
+                },
+                "args": [
+                  {
+                    "t": "var",
+                    "name": "rest"
+                  }
+                ]
               }
             }
           }
@@ -85,48 +176,151 @@
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
+            "args": [
+              {
                 "t": "app",
-            "fn": { "t": "var", "name": "count_zeros" },
+                "fn": {
-            "args": [{ "t": "ctor", "type": "List", "ctor": "Nil", "args": [] }]
+                  "t": "var",
-          }]
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "count_zeros"
+                    },
+                    "args": [
+                      {
+                        "t": "ctor",
+                        "type": "List",
+                        "ctor": "Nil",
+                        "args": []
+                      }
+                    ]
+                  }
+                ]
+              }
+            ]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [{
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
                 "t": "app",
-            "fn": { "t": "var", "name": "count_zeros" },
+                "fn": {
-            "args": [{
+                  "t": "var",
-              "t": "ctor", "type": "List", "ctor": "Cons",
+                  "name": "int_to_str"
+                },
                 "args": [
-                { "t": "lit", "lit": { "kind": "int", "value": 0 } },
                   {
-                  "t": "ctor", "type": "List", "ctor": "Cons",
+                    "t": "app",
+                    "fn": {
+                      "t": "var",
+                      "name": "count_zeros"
+                    },
                     "args": [
-                    { "t": "lit", "lit": { "kind": "int", "value": 5 } },
                       {
-                      "t": "ctor", "type": "List", "ctor": "Cons",
+                        "t": "ctor",
+                        "type": "List",
+                        "ctor": "Cons",
                         "args": [
-                        { "t": "lit", "lit": { "kind": "int", "value": 0 } },
                           {
-                          "t": "ctor", "type": "List", "ctor": "Cons",
+                            "t": "lit",
-                          "args": [
+                            "lit": {
-                            { "t": "lit", "lit": { "kind": "int", "value": 3 } },
+                              "kind": "int",
+                              "value": 0
+                            }
+                          },
                           {
-                              "t": "ctor", "type": "List", "ctor": "Cons",
+                            "t": "ctor",
+                            "type": "List",
+                            "ctor": "Cons",
                             "args": [
-                                { "t": "lit", "lit": { "kind": "int", "value": 0 } },
+                              {
-                                { "t": "ctor", "type": "List", "ctor": "Nil", "args": [] }
+                                "t": "lit",
+                                "lit": {
+                                  "kind": "int",
+                                  "value": 5
+                                }
+                              },
+                              {
+                                "t": "ctor",
+                                "type": "List",
+                                "ctor": "Cons",
+                                "args": [
+                                  {
+                                    "t": "lit",
+                                    "lit": {
+                                      "kind": "int",
+                                      "value": 0
+                                    }
+                                  },
+                                  {
+                                    "t": "ctor",
+                                    "type": "List",
+                                    "ctor": "Cons",
+                                    "args": [
+                                      {
+                                        "t": "lit",
+                                        "lit": {
+                                          "kind": "int",
+                                          "value": 3
+                                        }
+                                      },
+                                      {
+                                        "t": "ctor",
+                                        "type": "List",
+                                        "ctor": "Cons",
+                                        "args": [
+                                          {
+                                            "t": "lit",
+                                            "lit": {
+                                              "kind": "int",
+                                              "value": 0
+                                            }
+                                          },
+                                          {
+                                            "t": "ctor",
+                                            "type": "List",
+                                            "ctor": "Nil",
+                                            "args": []
+                                          }
                                         ]
                                       }
                                     ]
@@ -136,8 +330,26 @@
                             ]
                           }
                         ]
-            }]
+                      }
-          }]
+                    ]
+                  }
+                ]
+              }
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }

experiments/2026-05-12-cross-model-authoring/render/tests/spec_completeness.rs

@@ -16,7 +16,7 @@ use std::collections::HashSet;
 use std::path::PathBuf;
 
 use ailang_core::ast::{
-    Def, InstanceMethod, Literal, Module, ParamMode, Pattern, Term, Type,
+    Def, InstanceMethod, Literal, Module, NewArg, ParamMode, Pattern, Term, Type,
 };
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -41,6 +41,9 @@ enum VariantTag {
     TermSeq,
     TermClone,
     TermReuseAs,
+    TermLoop,
+    TermRecur,
+    TermNew,
     // Pattern
     PatternWild,
     PatternVar,
@@ -58,7 +61,6 @@ enum VariantTag {
     TypeVar,
     TypeForall,
     // ParamMode
-    ParamModeImplicit,
     ParamModeOwn,
     ParamModeBorrow,
 }
@@ -86,6 +88,9 @@ const EXPECTED_VARIANTS: &[VariantTag] = &[
     VariantTag::TermSeq,
     VariantTag::TermClone,
     VariantTag::TermReuseAs,
+    VariantTag::TermLoop,
+    VariantTag::TermRecur,
+    VariantTag::TermNew,
     VariantTag::PatternWild,
     VariantTag::PatternVar,
     VariantTag::PatternLit,
@@ -99,7 +104,6 @@ const EXPECTED_VARIANTS: &[VariantTag] = &[
     VariantTag::TypeFn,
     VariantTag::TypeVar,
     VariantTag::TypeForall,
-    VariantTag::ParamModeImplicit,
     VariantTag::ParamModeOwn,
     VariantTag::ParamModeBorrow,
 ];
@@ -222,6 +226,37 @@ fn visit_term(t: &Term, observed: &mut HashSet<VariantTag>) {
             visit_term(source, observed);
             visit_term(body, observed);
         }
+        Term::Loop { binders, body } => {
+            observed.insert(VariantTag::TermLoop);
+            for b in binders {
+                visit_type(&b.ty, observed);
+                visit_term(&b.init, observed);
+            }
+            visit_term(body, observed);
+        }
+        Term::Recur { args } => {
+            observed.insert(VariantTag::TermRecur);
+            for a in args {
+                visit_term(a, observed);
+            }
+        }
+        Term::New { type_name: _, args } => {
+            observed.insert(VariantTag::TermNew);
+            for a in args {
+                match a {
+                    NewArg::Type(t) => visit_type(t, observed),
+                    NewArg::Value(v) => visit_term(v, observed),
+                }
+            }
+        }
+        // `Intrinsic` is the compiler-supplied body marker — non-authorable
+        // (absent from the parser's term dispatch; typecheck enforces
+        // kernel-tier-only via IntrinsicOutsideKernelTier). A foreign-author
+        // mini-spec must not show it and no master example can legally
+        // contain it, so it is allowlisted OUT of completeness: no VariantTag,
+        // no EXPECTED entry, a no-op arm here so the match compiles without
+        // claiming coverage.
+        Term::Intrinsic => {}
     }
 }
 
@@ -297,9 +332,6 @@ fn visit_type(t: &Type, observed: &mut HashSet<VariantTag>) {
 
 fn visit_param_mode(m: &ParamMode, observed: &mut HashSet<VariantTag>) {
     match m {
-        ParamMode::Implicit => {
-            observed.insert(VariantTag::ParamModeImplicit);
-        }
         ParamMode::Own => {
             observed.insert(VariantTag::ParamModeOwn);
         }

experiments/2026-05-12-cross-model-authoring/rendered/ail.md

@@ -48,7 +48,7 @@ through this pair is gated by an integration test.
 (module fn_returns_int
   (fn answer
     (doc "The simplest possible fn — no params, returns a fixed Int.")
-    (type (fn-type (params) (ret (con Int))))
+    (type (fn-type (params) (ret (own (con Int)))))
     (params)
     (body 42)))
 ```
@@ -99,68 +99,57 @@ BODY-TYPE)`.
 (module forall_polymorphic
   (fn id
     (doc "The polymorphic identity function. Exercises Type::Forall and Type::Var.")
-    (type (forall (vars a) (fn-type (params a) (ret a))))
+    (type (forall (vars a) (fn-type (params (own a)) (ret (own a)))))
     (params x)
     (body x)))
 ```
 
 ## 4. Mode annotations
 
-Every function parameter carries a mode. The mode says how the
+Every function parameter carries a mode, and so does the return
-callee may treat the value: `implicit` is the legacy default
+position. There are exactly two modes. `own` means the caller
-(treated as `own`), `own` means the caller transfers ownership and
+transfers ownership and the callee consumes the value; `borrow`
-the callee consumes the value, `borrow` means the caller retains
+means the caller retains ownership and the callee may inspect but
-ownership and the callee may inspect but not consume.
+not consume. `borrow` is legal only over a boxed type (an algebraic
+data type): unboxed value types (`Int`, `Bool`, `Float`, `Unit`)
+are always `own`, and borrowing one is a `borrow-over-value` error.
 
-The mode also applies to the return value: `ret_mode` says whether
+The return position is always `own` — a function returns a fresh
-the function transfers ownership to the caller (`own`) or returns a
+owned value; borrow-returns are not permitted.
-borrow (`borrow`). For most functions the return mode is `own` or
-implicit; `borrow` returns are rare and used only for accessor-style
-functions.
 
-Modes are mandatory on every parameter and on the return position.
+Modes are mandatory: every parameter and the return position carries
-The schema rejects unannotated fn signatures only when annotations
+exactly one mode. There is no default or omitted mode.
-are explicitly requested; for compatibility the legacy form (no
-mode field at all) is treated as all-implicit.
 
 
 Modes are surface wrappers around the type in parameter and return
 position. Inside a `(fn-type ...)`:
 
 - `(params (own T1) (borrow T2))` — `T1` is owned, `T2` is borrowed.
-- `(ret (own T))` — the function returns an owned value.
+- `(ret (own T))` — the return is always owned.
-- A bare type with no mode wrapper is implicit (legacy default).
 
-When all parameters and the return are implicit, the surface omits
+Every parameter and the return carries a mode wrapper; there is no
-the mode wrappers entirely; this is the canonical form for fns that
+bare-type (mode-less) form. `borrow` is legal only over a boxed
-do not yet need explicit annotations. Adding modes is a forward
+type: `(borrow (con Int))` is a `borrow-over-value` error — write
-change: an existing fn keeps the same canonical bytes as long as no
+`(own (con Int))`. The mode is part of the fn's signature and
-annotation is added.
+contributes to its content hash.
-
-Writing `(borrow T)` on a parameter the typechecker wants `own`
-for surfaces as the `over-strict-mode` diagnostic — advisory, and
-suppressable via the fn def's `suppress` clause. The mode is part
-of the fn's signature and contributes to its content hash, so
-making the choice explicit at authoring time avoids surprise
-hash changes when the typechecker's defaults shift.
 
 ```ail
 (module param_modes_all
-  (fn f_implicit
+  (data List
-    (doc "Implicit mode is the legacy default — `param_modes` is omitted from canonical JSON when every entry is Implicit, which is the case here. The visitor still observes ParamMode::Implicit via the (defaulted) ret_mode field on Type::Fn.")
+    (ctor Nil)
-    (type (fn-type (params (con Int)) (ret (con Int))))
+    (ctor Cons (con Int) (con List)))
+  (fn f_own_value
+    (doc "(own Int) — unboxed value types (Int/Bool/Float/Unit) are always own; borrow over them is a borrow-over-value error.")
+    (type (fn-type (params (own (con Int))) (ret (own (con Int)))))
     (params x)
     (body x))
-  (fn f_own
+  (fn f_borrow_boxed
-    (doc "(own T) — caller transfers ownership; callee consumes.")
+    (doc "(borrow List) — boxed types may be borrowed; the callee reads without consuming.")
-    (type (fn-type (params (own (con Int))) (ret (con Int))))
+    (type (fn-type (params (borrow (con List))) (ret (own (con Int)))))
-    (params x)
+    (params xs)
-    (body x))
+    (body (match xs
-  (fn f_borrow
+      (case (pat-ctor Nil) 0)
-    (doc "(borrow T) — caller retains ownership; callee may not consume.")
+      (case (pat-ctor Cons h t) (app + 1 (app f_borrow_boxed t)))))))
-    (type (fn-type (params (borrow (con Int))) (ret (con Int))))
-    (params x)
-    (body x)))
 ```
 
 ## 5. Functions
@@ -211,7 +200,7 @@ number, a string is a double-quoted string, a bool is `true` or
 (module fn_calls_prelude
   (fn add
     (doc "Add two Ints via the polymorphic prelude `+`. Also exercises TermLet by binding the sum to a local name before returning it, and TermClone by re-using the let-bound value.")
-    (type (fn-type (params (con Int) (con Int)) (ret (con Int))))
+    (type (fn-type (params (own (con Int)) (own (con Int))) (ret (own (con Int)))))
     (params x y)
     (body (let s (app + x y) (clone s)))))
 ```
@@ -220,7 +209,7 @@ number, a string is a double-quoted string, a bool is `true` or
 (module fn_with_lambda
   (fn make_adder
     (doc "Curried adder: takes an Int and returns an Int -> Int closure. Exercises TermLam and Type::Fn appearing as a return type.")
-    (type (fn-type (params (con Int)) (ret (fn-type (params (con Int)) (ret (con Int))))))
+    (type (fn-type (params (own (con Int))) (ret (own (fn-type (params (own (con Int))) (ret (own (con Int))))))))
     (params x)
     (body (lam (params (typed y (con Int))) (ret (con Int)) (body (app + x y))))))
 ```
@@ -264,13 +253,12 @@ element list.
 ```ail
 (module data_simple
   (data Box (vars a)
-    (doc "A unary box around a polymorphic value.")
     (ctor MkBox a))
   (fn wrap_one
-    (doc "Construct a Box Int via MkBox. The body uses (reuse-as src body) — a hint that the freshly-allocated Box should reuse the source's memory slot under --alloc=rc. Exercises TermCtor, ReuseAs, and Type::Var inside a ctor field position.")
     (type (fn-type (params (own (con Box (con Int)))) (ret (own (con Box (con Int))))))
     (params src)
-    (body (reuse-as src (term-ctor Box MkBox 1)))))
+    (body (match src
+      (case (pat-ctor MkBox v) (reuse-as src (term-ctor Box MkBox 1)))))))
 ```
 
 ## 7. Pattern matching
@@ -319,16 +307,16 @@ arms or into code outside the `match`.
     (ctor Cons (con Int) (con List)))
   (fn head_or_zero
     (doc "Return the head of xs, or 0 if empty. Exercises TermMatch with two arms, PatternCtor (both nullary Nil and binary Cons), and PatternWild on the tail field.")
-    (type (fn-type (params (borrow (con List))) (ret (con Int))))
+    (type (fn-type (params (borrow (con List))) (ret (own (con Int)))))
     (params xs)
     (body (match xs
       (case (pat-ctor Nil) 0)
       (case (pat-ctor Cons h _) h))))
   (fn count_via_letrec
     (doc "Walk xs counting nodes using a local recursive let. Exercises TermLetRec and TermVar; the recursive `go` is bound locally.")
-    (type (fn-type (params (borrow (con List))) (ret (con Int))))
+    (type (fn-type (params (own (con List))) (ret (own (con Int)))))
     (params xs)
-    (body (let-rec go (params ys) (type (fn-type (params (borrow (con List))) (ret (con Int)))) (body (match ys
+    (body (let-rec go (params ys) (type (fn-type (params (own (con List))) (ret (own (con Int))))) (body (match ys
       (case (pat-ctor Nil) 0)
       (case (pat-ctor Cons _ t) (app + 1 (app go t))))) (in (app go xs))))))
 ```
@@ -337,16 +325,16 @@ arms or into code outside the `match`.
 (module match_literal_pattern
   (fn classify
     (doc "Classify an Int via literal patterns plus a wildcard fallback. Exercises PatternLit and PatternWild.")
-    (type (fn-type (params (con Int)) (ret (con Int))))
+    (type (fn-type (params (own (con Int))) (ret (own (con Int)))))
     (params n)
     (body (match n
       (case (pat-lit 0) 100)
       (case _ 200))))
   (fn sign_if
     (doc "Return -1 / 0 / 1 for the sign of n using nested TermIf. Exercises TermIf in both then/else positions plus TermApp on the polymorphic comparison.")
-    (type (fn-type (params (con Int)) (ret (con Int))))
+    (type (fn-type (params (own (con Int))) (ret (own (con Int)))))
     (params n)
-    (body (if (app < n 0) -1 (if (app == n 0) 0 1)))))
+    (body (if (app lt n 0) -1 (if (app eq n 0) 0 1)))))
 ```
 
 ## 8. Effects
@@ -390,9 +378,9 @@ value.
 (module fn_with_do_seq
   (fn main
     (doc "Print two Ints in sequence. Exercises TermDo, TermSeq, and the IO effect on a fn type. The trailing unit return is implicit in the last Do (op returns Unit).")
-    (type (fn-type (params) (ret (con Unit)) (effects IO)))
+    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
     (params)
-    (body (seq (do io/print_int 1) (do io/print_int 2)))))
+    (body (seq (seq (do io/print_str (app int_to_str 1)) (do io/print_str "\n")) (seq (do io/print_str (app int_to_str 2)) (do io/print_str "\n"))))))
 ```
 
 ## 9. Literals
@@ -447,17 +435,17 @@ authoring surface; for non-finite values use the prelude constants
 (module bool_str
   (fn is_true
     (doc "Trivial Bool literal. Exercises Literal::Bool.")
-    (type (fn-type (params) (ret (con Bool))))
+    (type (fn-type (params) (ret (own (con Bool)))))
     (params)
     (body true))
   (fn greeting
     (doc "Trivial Str literal. Exercises Literal::Str.")
-    (type (fn-type (params) (ret (con Str))))
+    (type (fn-type (params) (ret (own (con Str)))))
     (params)
     (body "hi"))
   (fn unit_value
     (doc "Trivial Unit literal — needed so Literal::Unit appears at least once in the corpus.")
-    (type (fn-type (params) (ret (con Unit))))
+    (type (fn-type (params) (ret (own (con Unit)))))
     (params)
     (body (lit-unit))))
 ```
@@ -508,7 +496,7 @@ also legal (typically a typecheck error unless an instance exists).
     (param a)
     (doc "A toy single-method class. The instance in instance_def.ail.json provides a body for `show` at type Int.")
     (method show
-      (type (fn-type (params a) (ret (con Str)))))))
+      (type (fn-type (params (own a)) (ret (own (con Str))))))))
 ```
 
 ```ail
@@ -517,7 +505,7 @@ also legal (typically a typecheck error unless an instance exists).
     (param a)
     (doc "Re-declared here so this fixture is self-contained; class_def.ail.json declares the same class verbatim.")
     (method show
-      (type (fn-type (params a) (ret (con Str))))))
+      (type (fn-type (params (own a)) (ret (own (con Str)))))))
   (instance
     (class MyShow)
     (type (con Int))

experiments/2026-05-12-cross-model-authoring/rendered/json.md

@@ -58,7 +58,9 @@ carries a `kind` discriminator.
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -123,7 +125,9 @@ optional `constraints` array for class constraints (see section 10).
         "body": {
           "k": "fn",
           "params": [ { "k": "var", "name": "a" } ],
+          "param_modes": ["own"],
           "ret": { "k": "var", "name": "a" },
+          "ret_mode": "own",
           "effects": []
         }
       },
@@ -136,89 +140,34 @@ optional `constraints` array for class constraints (see section 10).
 
 ## 4. Mode annotations
 
-Every function parameter carries a mode. The mode says how the
+Every function parameter carries a mode, and so does the return
-callee may treat the value: `implicit` is the legacy default
+position. There are exactly two modes. `own` means the caller
-(treated as `own`), `own` means the caller transfers ownership and
+transfers ownership and the callee consumes the value; `borrow`
-the callee consumes the value, `borrow` means the caller retains
+means the caller retains ownership and the callee may inspect but
-ownership and the callee may inspect but not consume.
+not consume. `borrow` is legal only over a boxed type (an algebraic
+data type): unboxed value types (`Int`, `Bool`, `Float`, `Unit`)
+are always `own`, and borrowing one is a `borrow-over-value` error.
 
-The mode also applies to the return value: `ret_mode` says whether
+The return position is always `own` — a function returns a fresh
-the function transfers ownership to the caller (`own`) or returns a
+owned value; borrow-returns are not permitted.
-borrow (`borrow`). For most functions the return mode is `own` or
-implicit; `borrow` returns are rare and used only for accessor-style
-functions.
 
-Modes are mandatory on every parameter and on the return position.
+Modes are mandatory: every parameter and the return position carries
-The schema rejects unannotated fn signatures only when annotations
+exactly one mode. There is no default or omitted mode.
-are explicitly requested; for compatibility the legacy form (no
-mode field at all) is treated as all-implicit.
 
-On `Type::Fn`, two optional fields carry modes:
+On `Type::Fn`, two required fields carry modes:
 
-- `param_modes`: array of strings `"implicit"`, `"own"`, or
+- `param_modes`: an array of strings, each `"own"` or `"borrow"`,
-  `"borrow"`, one per parameter, in the same order as `params`. The
+  one per parameter, in the same order as `params`.
-  array is omitted from the canonical bytes when every entry is
+- `ret_mode`: a single string, always `"own"`.
-  `"implicit"`; this is purely a serialisation optimisation. Author
-  the field explicitly when at least one parameter is `own` or
-  `borrow`.
-- `ret_mode`: a single string of the same vocabulary. Omitted when
-  it would be `"implicit"`.
 
-Example: a fn that borrows two ints and returns an int:
+Both are present on every fn type. Example — a fn that borrows a
-`"param_modes": ["borrow", "borrow"]`, `ret_mode` omitted (implicit).
+boxed list and returns an int: `"param_modes": ["borrow"]`,
-A fn that consumes a list and returns a new list:
+`"ret_mode": "own"`. A fn that consumes an int and returns an int:
 `"param_modes": ["own"]`, `"ret_mode": "own"`.
 
 
 ```json
-{
+{"defs":[{"ctors":[{"fields":[],"name":"Nil"},{"fields":[{"k":"con","name":"Int"},{"k":"con","name":"List"}],"name":"Cons"}],"kind":"type","name":"List"},{"body":{"name":"x","t":"var"},"doc":"(own Int) — unboxed value types (Int/Bool/Float/Unit) are always own; borrow over them is a borrow-over-value error.","kind":"fn","name":"f_own_value","params":["x"],"type":{"effects":[],"k":"fn","param_modes":["own"],"params":[{"k":"con","name":"Int"}],"ret":{"k":"con","name":"Int"},"ret_mode":"own"}},{"body":{"arms":[{"body":{"lit":{"kind":"int","value":0},"t":"lit"},"pat":{"ctor":"Nil","fields":[],"p":"ctor"}},{"body":{"args":[{"lit":{"kind":"int","value":1},"t":"lit"},{"args":[{"name":"t","t":"var"}],"fn":{"name":"f_borrow_boxed","t":"var"},"t":"app"}],"fn":{"name":"+","t":"var"},"t":"app"},"pat":{"ctor":"Cons","fields":[{"name":"h","p":"var"},{"name":"t","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"xs","t":"var"},"t":"match"},"doc":"(borrow List) — boxed types may be borrowed; the callee reads without consuming.","kind":"fn","name":"f_borrow_boxed","params":["xs"],"type":{"effects":[],"k":"fn","param_modes":["borrow"],"params":[{"k":"con","name":"List"}],"ret":{"k":"con","name":"Int"},"ret_mode":"own"}}],"imports":[],"name":"param_modes_all","schema":"ailang/v0"}
-  "schema": "ailang/v0",
-  "name": "param_modes_all",
-  "imports": [],
-  "defs": [
-    {
-      "kind": "fn",
-      "name": "f_implicit",
-      "doc": "Implicit mode is the legacy default — `param_modes` is omitted from canonical JSON when every entry is Implicit, which is the case here. The visitor still observes ParamMode::Implicit via the (defaulted) ret_mode field on Type::Fn.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    },
-    {
-      "kind": "fn",
-      "name": "f_own",
-      "doc": "(own T) — caller transfers ownership; callee consumes.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "param_modes": ["own"],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    },
-    {
-      "kind": "fn",
-      "name": "f_borrow",
-      "doc": "(borrow T) — caller retains ownership; callee may not consume.",
-      "type": {
-        "k": "fn",
-        "params": [ { "k": "con", "name": "Int" } ],
-        "param_modes": ["borrow"],
-        "ret": { "k": "con", "name": "Int" },
-        "effects": []
-      },
-      "params": ["x"],
-      "body": { "t": "var", "name": "x" }
-    }
-  ]
-}
 ```
 
 ## 5. Functions
@@ -279,7 +228,9 @@ the difference.
           { "k": "con", "name": "Int" },
           { "k": "con", "name": "Int" }
         ],
+        "param_modes": ["own", "own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["x", "y"],
@@ -314,20 +265,24 @@ the difference.
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": {
           "k": "fn",
           "params": [ { "k": "con", "name": "Int" } ],
+          "param_modes": ["own"],
           "ret": { "k": "con", "name": "Int" },
+          "ret_mode": "own",
           "effects": []
         },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["x"],
       "body": {
         "t": "lam",
         "params": ["y"],
-        "paramTypes": [ { "k": "con", "name": "Int" } ],
+        "param-types": [ { "k": "con", "name": "Int" } ],
-        "retType": { "k": "con", "name": "Int" },
+        "ret-type": { "k": "con", "name": "Int" },
         "effects": [],
         "body": {
           "t": "app",
@@ -378,51 +333,7 @@ carry `"args": []`.
 
 
 ```json
-{
+{"defs":[{"ctors":[{"fields":[{"k":"var","name":"a"}],"name":"MkBox"}],"kind":"type","name":"Box","vars":["a"]},{"body":{"arms":[{"body":{"body":{"args":[{"lit":{"kind":"int","value":1},"t":"lit"}],"ctor":"MkBox","t":"ctor","type":"Box"},"source":{"name":"src","t":"var"},"t":"reuse-as"},"pat":{"ctor":"MkBox","fields":[{"name":"v","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"src","t":"var"},"t":"match"},"kind":"fn","name":"wrap_one","params":["src"],"type":{"effects":[],"k":"fn","param_modes":["own"],"params":[{"args":[{"k":"con","name":"Int"}],"k":"con","name":"Box"}],"ret":{"args":[{"k":"con","name":"Int"}],"k":"con","name":"Box"},"ret_mode":"own"}}],"imports":[],"name":"data_simple","schema":"ailang/v0"}
-  "schema": "ailang/v0",
-  "name": "data_simple",
-  "imports": [],
-  "defs": [
-    {
-      "kind": "type",
-      "name": "Box",
-      "vars": ["a"],
-      "doc": "A unary box around a polymorphic value.",
-      "ctors": [
-        {
-          "name": "MkBox",
-          "fields": [ { "k": "var", "name": "a" } ]
-        }
-      ]
-    },
-    {
-      "kind": "fn",
-      "name": "wrap_one",
-      "doc": "Construct a Box Int via MkBox. The body uses (reuse-as src body) — a hint that the freshly-allocated Box should reuse the source's memory slot under --alloc=rc. Exercises TermCtor, ReuseAs, and Type::Var inside a ctor field position.",
-      "type": {
-        "k": "fn",
-        "params": [
-          { "k": "con", "name": "Box", "args": [ { "k": "con", "name": "Int" } ] }
-        ],
-        "param_modes": ["own"],
-        "ret": { "k": "con", "name": "Box", "args": [ { "k": "con", "name": "Int" } ] },
-        "ret_mode": "own",
-        "effects": []
-      },
-      "params": ["src"],
-      "body": {
-        "t": "reuse-as",
-        "source": { "t": "var", "name": "src" },
-        "body": {
-          "t": "ctor",
-          "type": "Box",
-          "ctor": "MkBox",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 1 } } ]
-        }
-      }
-    }
-  ]
-}
 ```
 
 ## 7. Pattern matching
@@ -470,14 +381,23 @@ single pattern. Repeating a name is a typecheck error.
     {
       "kind": "type",
       "name": "List",
-      "doc": "Monomorphic singly-linked Int list — boxed, recursive.",
+      "doc": "Monomorphic singly-linked Int list \u2014 boxed, recursive.",
       "ctors": [
-        { "name": "Nil", "fields": [] },
+        {
+          "name": "Nil",
+          "fields": []
+        },
         {
           "name": "Cons",
           "fields": [
-            { "k": "con", "name": "Int" },
+            {
-            { "k": "con", "name": "List" }
+              "k": "con",
+              "name": "Int"
+            },
+            {
+              "k": "con",
+              "name": "List"
+            }
           ]
         }
       ]
@@ -488,30 +408,64 @@ single pattern. Repeating a name is a typecheck error.
       "doc": "Return the head of xs, or 0 if empty. Exercises TermMatch with two arms, PatternCtor (both nullary Nil and binary Cons), and PatternWild on the tail field.",
       "type": {
         "k": "fn",
-        "params": [ { "k": "con", "name": "List" } ],
+        "params": [
-        "param_modes": ["borrow"],
+          {
-        "ret": { "k": "con", "name": "Int" },
+            "k": "con",
+            "name": "List"
+          }
+        ],
+        "param_modes": [
+          "borrow"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "match",
-        "scrutinee": { "t": "var", "name": "xs" },
+        "scrutinee": {
+          "t": "var",
+          "name": "xs"
+        },
         "arms": [
           {
-            "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+            "pat": {
-            "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+              "p": "ctor",
+              "ctor": "Nil",
+              "fields": []
+            },
+            "body": {
+              "t": "lit",
+              "lit": {
+                "kind": "int",
+                "value": 0
+              }
+            }
           },
           {
             "pat": {
               "p": "ctor",
               "ctor": "Cons",
               "fields": [
-                { "p": "var", "name": "h" },
+                {
-                { "p": "wild" }
+                  "p": "var",
+                  "name": "h"
+                },
+                {
+                  "p": "wild"
+                }
               ]
             },
-            "body": { "t": "var", "name": "h" }
+            "body": {
+              "t": "var",
+              "name": "h"
+            }
           }
         ]
       }
@@ -522,49 +476,110 @@ single pattern. Repeating a name is a typecheck error.
       "doc": "Walk xs counting nodes using a local recursive let. Exercises TermLetRec and TermVar; the recursive `go` is bound locally.",
       "type": {
         "k": "fn",
-        "params": [ { "k": "con", "name": "List" } ],
+        "params": [
-        "param_modes": ["borrow"],
+          {
-        "ret": { "k": "con", "name": "Int" },
+            "k": "con",
+            "name": "List"
+          }
+        ],
+        "param_modes": [
+          "own"
+        ],
+        "ret": {
+          "k": "con",
+          "name": "Int"
+        },
+        "ret_mode": "own",
         "effects": []
       },
-      "params": ["xs"],
+      "params": [
+        "xs"
+      ],
       "body": {
         "t": "letrec",
         "name": "go",
         "type": {
           "k": "fn",
-          "params": [ { "k": "con", "name": "List" } ],
+          "params": [
-          "param_modes": ["borrow"],
+            {
-          "ret": { "k": "con", "name": "Int" },
+              "k": "con",
+              "name": "List"
+            }
+          ],
+          "param_modes": [
+            "own"
+          ],
+          "ret": {
+            "k": "con",
+            "name": "Int"
+          },
+          "ret_mode": "own",
           "effects": []
         },
-        "params": ["ys"],
+        "params": [
+          "ys"
+        ],
         "body": {
           "t": "match",
-          "scrutinee": { "t": "var", "name": "ys" },
+          "scrutinee": {
+            "t": "var",
+            "name": "ys"
+          },
           "arms": [
             {
-              "pat": { "p": "ctor", "ctor": "Nil", "fields": [] },
+              "pat": {
-              "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+                "p": "ctor",
+                "ctor": "Nil",
+                "fields": []
+              },
+              "body": {
+                "t": "lit",
+                "lit": {
+                  "kind": "int",
+                  "value": 0
+                }
+              }
             },
             {
               "pat": {
                 "p": "ctor",
                 "ctor": "Cons",
                 "fields": [
-                  { "p": "wild" },
+                  {
-                  { "p": "var", "name": "t" }
+                    "p": "wild"
+                  },
+                  {
+                    "p": "var",
+                    "name": "t"
+                  }
                 ]
               },
               "body": {
                 "t": "app",
-                "fn": { "t": "var", "name": "+" },
+                "fn": {
+                  "t": "var",
+                  "name": "+"
+                },
                 "args": [
-                  { "t": "lit", "lit": { "kind": "int", "value": 1 } },
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1
+                    }
+                  },
                   {
                     "t": "app",
-                    "fn": { "t": "var", "name": "go" },
+                    "fn": {
-                    "args": [ { "t": "var", "name": "t" } ]
+                      "t": "var",
+                      "name": "go"
+                    },
+                    "args": [
+                      {
+                        "t": "var",
+                        "name": "t"
+                      }
+                    ]
                   }
                 ]
               }
@@ -573,8 +588,16 @@ single pattern. Repeating a name is a typecheck error.
         },
         "in": {
           "t": "app",
-          "fn": { "t": "var", "name": "go" },
+          "fn": {
-          "args": [ { "t": "var", "name": "xs" } ]
+            "t": "var",
+            "name": "go"
+          },
+          "args": [
+            {
+              "t": "var",
+              "name": "xs"
+            }
+          ]
         }
       }
     }
@@ -595,7 +618,9 @@ single pattern. Repeating a name is a typecheck error.
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["n"],
@@ -621,7 +646,9 @@ single pattern. Repeating a name is a typecheck error.
       "type": {
         "k": "fn",
         "params": [ { "k": "con", "name": "Int" } ],
+        "param_modes": ["own"],
         "ret": { "k": "con", "name": "Int" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": ["n"],
@@ -629,7 +656,7 @@ single pattern. Repeating a name is a typecheck error.
         "t": "if",
         "cond": {
           "t": "app",
-          "fn": { "t": "var", "name": "<" },
+          "fn": { "t": "var", "name": "lt" },
           "args": [
             { "t": "var", "name": "n" },
             { "t": "lit", "lit": { "kind": "int", "value": 0 } }
@@ -640,7 +667,7 @@ single pattern. Repeating a name is a typecheck error.
           "t": "if",
           "cond": {
             "t": "app",
-            "fn": { "t": "var", "name": "==" },
+            "fn": { "t": "var", "name": "eq" },
             "args": [
               { "t": "var", "name": "n" },
               { "t": "lit", "lit": { "kind": "int", "value": 0 } }
@@ -704,21 +731,94 @@ discarded but its effects count toward the enclosing fn's row.
       "type": {
         "k": "fn",
         "params": [],
-        "ret": { "k": "con", "name": "Unit" },
+        "param_modes": [],
-        "effects": ["IO"]
+        "ret": {
+          "k": "con",
+          "name": "Unit"
+        },
+        "ret_mode": "own",
+        "effects": [
+          "IO"
+        ]
       },
       "params": [],
       "body": {
+        "t": "seq",
+        "lhs": {
           "t": "seq",
           "lhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 1 } } ]
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 1
+                    }
+                  }
+                ]
+              }
+            ]
           },
           "rhs": {
             "t": "do",
-          "op": "io/print_int",
+            "op": "io/print_str",
-          "args": [ { "t": "lit", "lit": { "kind": "int", "value": 2 } } ]
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
+        },
+        "rhs": {
+          "t": "seq",
+          "lhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "app",
+                "fn": {
+                  "t": "var",
+                  "name": "int_to_str"
+                },
+                "args": [
+                  {
+                    "t": "lit",
+                    "lit": {
+                      "kind": "int",
+                      "value": 2
+                    }
+                  }
+                ]
+              }
+            ]
+          },
+          "rhs": {
+            "t": "do",
+            "op": "io/print_str",
+            "args": [
+              {
+                "t": "lit",
+                "lit": {
+                  "kind": "str",
+                  "value": "\n"
+                }
+              }
+            ]
+          }
         }
       }
     }
@@ -795,7 +895,9 @@ not by the author. When you write `3.14` in AIL, the parser emits
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Bool" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -808,7 +910,9 @@ not by the author. When you write `3.14` in AIL, the parser emits
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Str" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -821,7 +925,9 @@ not by the author. When you write `3.14` in AIL, the parser emits
       "type": {
         "k": "fn",
         "params": [],
+        "param_modes": [],
         "ret": { "k": "con", "name": "Unit" },
+        "ret_mode": "own",
         "effects": []
       },
       "params": [],
@@ -889,7 +995,9 @@ constraints; omitted from canonical bytes when empty.
           "type": {
             "k": "fn",
             "params": [ { "k": "var", "name": "a" } ],
+            "param_modes": ["own"],
             "ret": { "k": "con", "name": "Str" },
+            "ret_mode": "own",
             "effects": []
           }
         }
@@ -916,7 +1024,9 @@ constraints; omitted from canonical bytes when empty.
           "type": {
             "k": "fn",
             "params": [ { "k": "var", "name": "a" } ],
+            "param_modes": ["own"],
             "ret": { "k": "con", "name": "Str" },
+            "ret_mode": "own",
             "effects": []
           }
         }