Iter 15d: std_either ships — 2-type-var ADT + 3-type-var eliminator
Third stdlib module. Either<e, a> is the first 2-type-var data def, and the eliminator `either : (e -> c) -> (a -> c) -> Either<e, a> -> c` the first fn with three type vars on top of the data — the deepest polymorphism shipped end-to-end so far. Five combinators: from_right, is_left, is_right, map_right, either. Demo exercises every one and runs to deterministic output. IR shows six distinct monomorphisations including two `from_right` variants (Left=Int vs Left=$u depending on call site) and `either__I_I_I`. No new compiler bugs surfaced: 14a / 14h / 15b coverage was wide enough to handle 2-type-var data plus 3-type-var fns out of the box. Discovered (queued as 15e): `ail render` and `ail parse` are not symmetric. Form-(A) printer in ailang_surface::print is the actual inverse of `parse` (round-trip test covers it across all 25 fixtures including std_either) but is not exposed via the CLI; `render` still calls the older ailang_core::pretty::module printer. Tests: 89/89 (was 88, +1 e2e for std_either_demo). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
@@ -305,6 +305,26 @@ fn std_list_stress_1000_element_folds() {
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);
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}
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/// Iter 15d: `std_either` end-to-end. First stdlib ADT with two type
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/// parameters (`Either<e, a>`); first combinator with three type vars
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/// (`either : (e -> c) -> (a -> c) -> Either<e, a> -> c`).
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///
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/// Property protected: monomorphisation correctly distinguishes per-
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/// call-site instantiations, including (a) two `from_right` instances
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/// differing only in the unused `e` (Int vs $u) and (b) the
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/// 3-type-var `either__I_I_I` instantiation. If wildcard substitution
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/// regressed, one of those would either fail to emit or collide with
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/// another instantiation.
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#[test]
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fn std_either_demo() {
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let stdout = build_and_run("std_either_demo.ail.json");
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let lines: Vec<&str> = stdout.lines().collect();
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assert_eq!(
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lines,
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vec!["42", "99", "true", "true", "42", "6", "101"]
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);
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}
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/// Guards `ail diff`: a modified body changes the hash of `sum`, while
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/// `main` stays unchanged. Expects exit code 1, `changed` contains exactly
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/// `sum`, `unchanged` contains `main`, `added`/`removed` empty.
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@@ -2515,3 +2515,94 @@ the stdlib can grow without them.
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---
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## Iter 15d — `std_either`: 2-type-var ADT + 3-type-var eliminator
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**Goal.** Third stdlib module. Either is the canonical 2-type-var
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disjoint sum. The eliminator combinator `either : (e → c) → (a → c) →
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Either<e, a> → c` introduces a third type var on top of the data,
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making it the most polymorphism-dense fn shipped to date.
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**What shipped.**
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- `examples/std_either.ailx` (74 LOC). Defines `Either e a = Left e | Right a`
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plus 5 combinators:
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- `from_right : a → Either<e, a> → a` — eliminate Right or use default.
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- `is_left`, `is_right : Either<e, a> → Bool`.
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- `map_right : (a → b) → Either<e, a> → Either<e, b>` —
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Functor-style on the Right side.
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- `either : (e → c) → (a → c) → Either<e, a> → c` —
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catamorphism / fold-on-sum.
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- `examples/std_either_demo.ailx` exercises every combinator,
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including the eliminator with two distinct concrete instantiations
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(over `Left 5` and over `Right 100`).
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- Canonical JSON for both, parsed via `ail parse`, type-checked,
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built, and executed end-to-end.
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**Output (deterministic).**
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```
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42 ; from_right 0 (Right 42)
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99 ; from_right 99 (Left 7)
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true ; is_left (Left 7)
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true ; is_right (Right 42)
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42 ; from_right 0 (map_right inc (Right 41))
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6 ; either inc inc (Left 5)
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101 ; either inc inc (Right 100)
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```
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**Monomorphisation evidence.** Six distinct instantiations across the
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five combinators, all generated correctly with the `$u` wildcard for
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unused type-var positions:
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```
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@ail_std_either_from_right__I_I ; e=Int, a=Int
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@ail_std_either_from_right__U_I ; e=$u, a=Int
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@ail_std_either_is_left__I_U ; e=Int, a=$u
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@ail_std_either_is_right__U_I ; e=$u, a=Int
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@ail_std_either_map_right__U_I_I ; e=$u, a=Int, b=Int
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@ail_std_either_either__I_I_I ; e=Int, a=Int, c=Int
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```
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The two `from_right` variants are notable: same source fn, two
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different concrete `e` per call site (Int when scrutinee is Left 7;
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$u when scrutinee is Right _ since Left's payload is unused). The
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14a monomorphisation machinery picks the right one per site without
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extra ceremony.
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The 3-type-var instantiation `either__I_I_I` is the deepest type
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substitution shipped through monomorphisation so far. Both call
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sites in main hit the same instantiation (`e=a=c=Int`) so a single
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emit suffices.
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**No new compiler bugs surfaced.** First stdlib iter without a fresh
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codegen/check fix. Indicator that 14a / 14h / 15b coverage was wide
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enough to handle 2-type-var data + 3-type-var fns out of the box.
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**Discovered (not fixed in this iter):** `ail render` and `ail parse`
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are not symmetric, despite the help text in the CLI claiming they
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are. `render` calls the older `ailang_core::pretty::module`
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human-pretty printer (form B-ish), while `parse` consumes form (A).
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The form-(A) printer in `ailang_surface::print` is correctly the
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inverse of `parse` — confirmed by the round-trip test in
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`crates/ailang-surface/tests/round_trip.rs` which now covers 25
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fixtures including `std_either.ail.json` — but it is not exposed via
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the CLI. Logged as 15e.
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**Tests: 89/89 (was 88, +1 e2e for std_either_demo).** Cumulative
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31 e2e tests.
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**Cumulative state, post-15d.**
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- Stdlib modules: 3 (`std_maybe`, `std_list`, `std_either`).
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- Combinators: 19.
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- Type-system surface area exercised: 1-type-var data (Maybe, List
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with recursion) and 2-type-var data (Either); 1- and 2- and
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3-type-var polymorphic fns; cross-module recursive ADTs;
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monomorphisation-with-wildcards across all.
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**Queue update.** 15d done; remaining queue: 15e (CLI render/parse
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symmetry — small, just discovered), then `std_pair` if more stdlib
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is wanted, then 16a/16b language gaps.
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@@ -0,0 +1 @@
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{"defs":[{"ctors":[{"fields":[{"k":"var","name":"e"}],"name":"Left"},{"fields":[{"k":"var","name":"a"}],"name":"Right"}],"doc":"Disjoint sum: Left<e> for the failure branch, Right<a> for the success branch. Right is the conventional 'success' side.","kind":"type","name":"Either","vars":["e","a"]},{"body":{"arms":[{"body":{"name":"v","t":"var"},"pat":{"ctor":"Right","fields":[{"name":"v","p":"var"}],"p":"ctor"}},{"body":{"name":"default","t":"var"},"pat":{"ctor":"Left","fields":[{"p":"wild"}],"p":"ctor"}}],"scrutinee":{"name":"x","t":"var"},"t":"match"},"doc":"Project the Right<a> payload, or use the default for Left<_>.","kind":"fn","name":"from_right","params":["default","x"],"type":{"body":{"effects":[],"k":"fn","params":[{"k":"var","name":"a"},{"args":[{"k":"var","name":"e"},{"k":"var","name":"a"}],"k":"con","name":"Either"}],"ret":{"k":"var","name":"a"}},"k":"forall","vars":["e","a"]}},{"body":{"arms":[{"body":{"lit":{"kind":"bool","value":true},"t":"lit"},"pat":{"ctor":"Left","fields":[{"p":"wild"}],"p":"ctor"}},{"body":{"lit":{"kind":"bool","value":false},"t":"lit"},"pat":{"ctor":"Right","fields":[{"p":"wild"}],"p":"ctor"}}],"scrutinee":{"name":"x","t":"var"},"t":"match"},"doc":"Returns true iff x is Left<_>.","kind":"fn","name":"is_left","params":["x"],"type":{"body":{"effects":[],"k":"fn","params":[{"args":[{"k":"var","name":"e"},{"k":"var","name":"a"}],"k":"con","name":"Either"}],"ret":{"k":"con","name":"Bool"}},"k":"forall","vars":["e","a"]}},{"body":{"arms":[{"body":{"lit":{"kind":"bool","value":false},"t":"lit"},"pat":{"ctor":"Left","fields":[{"p":"wild"}],"p":"ctor"}},{"body":{"lit":{"kind":"bool","value":true},"t":"lit"},"pat":{"ctor":"Right","fields":[{"p":"wild"}],"p":"ctor"}}],"scrutinee":{"name":"x","t":"var"},"t":"match"},"doc":"Returns true iff x is Right<_>.","kind":"fn","name":"is_right","params":["x"],"type":{"body":{"effects":[],"k":"fn","params":[{"args":[{"k":"var","name":"e"},{"k":"var","name":"a"}],"k":"con","name":"Either"}],"ret":{"k":"con","name":"Bool"}},"k":"forall","vars":["e","a"]}},{"body":{"arms":[{"body":{"args":[{"args":[{"name":"v","t":"var"}],"fn":{"name":"f","t":"var"},"t":"app"}],"ctor":"Right","t":"ctor","type":"Either"},"pat":{"ctor":"Right","fields":[{"name":"v","p":"var"}],"p":"ctor"}},{"body":{"args":[{"name":"l","t":"var"}],"ctor":"Left","t":"ctor","type":"Either"},"pat":{"ctor":"Left","fields":[{"name":"l","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"x","t":"var"},"t":"match"},"doc":"Apply f to the Right<a> payload; pass Left<e> through untouched.","kind":"fn","name":"map_right","params":["f","x"],"type":{"body":{"effects":[],"k":"fn","params":[{"effects":[],"k":"fn","params":[{"k":"var","name":"a"}],"ret":{"k":"var","name":"b"}},{"args":[{"k":"var","name":"e"},{"k":"var","name":"a"}],"k":"con","name":"Either"}],"ret":{"args":[{"k":"var","name":"e"},{"k":"var","name":"b"}],"k":"con","name":"Either"}},"k":"forall","vars":["e","a","b"]}},{"body":{"arms":[{"body":{"args":[{"name":"l","t":"var"}],"fn":{"name":"on_left","t":"var"},"t":"app"},"pat":{"ctor":"Left","fields":[{"name":"l","p":"var"}],"p":"ctor"}},{"body":{"args":[{"name":"r","t":"var"}],"fn":{"name":"on_right","t":"var"},"t":"app"},"pat":{"ctor":"Right","fields":[{"name":"r","p":"var"}],"p":"ctor"}}],"scrutinee":{"name":"x","t":"var"},"t":"match"},"doc":"Eliminator: apply on_left to a Left payload, on_right to a Right payload, fold both branches into the same result type c.","kind":"fn","name":"either","params":["on_left","on_right","x"],"type":{"body":{"effects":[],"k":"fn","params":[{"effects":[],"k":"fn","params":[{"k":"var","name":"e"}],"ret":{"k":"var","name":"c"}},{"effects":[],"k":"fn","params":[{"k":"var","name":"a"}],"ret":{"k":"var","name":"c"}},{"args":[{"k":"var","name":"e"},{"k":"var","name":"a"}],"k":"con","name":"Either"}],"ret":{"k":"var","name":"c"}},"k":"forall","vars":["e","a","c"]}}],"imports":[],"name":"std_either","schema":"ailang/v0"}
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@@ -0,0 +1,81 @@
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; Iter 15d — third stdlib module: tagged-disjoint values.
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; Either<e, a> is the canonical 2-type-var ADT. First stdlib module
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; with two type parameters; first to ship an eliminator combinator
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; (`either`) that introduces a third type var on top of the data.
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(module std_either
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(data Either (vars e a)
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(doc "Disjoint sum: Left<e> for the failure branch, Right<a> for the success branch. Right is the conventional 'success' side.")
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(ctor Left e)
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(ctor Right a))
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(fn from_right
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(doc "Project the Right<a> payload, or use the default for Left<_>.")
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(type
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(forall (vars e a)
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(fn-type
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(params a (con Either e a))
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(ret a))))
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(params default x)
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(body
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(match x
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(case (pat-ctor Right v) v)
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(case (pat-ctor Left _) default))))
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(fn is_left
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(doc "Returns true iff x is Left<_>.")
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(type
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(forall (vars e a)
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(fn-type
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(params (con Either e a))
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(ret (con Bool)))))
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(params x)
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(body
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(match x
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(case (pat-ctor Left _) true)
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(case (pat-ctor Right _) false))))
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(fn is_right
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(doc "Returns true iff x is Right<_>.")
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(type
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(forall (vars e a)
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(fn-type
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(params (con Either e a))
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(ret (con Bool)))))
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(params x)
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(body
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(match x
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(case (pat-ctor Left _) false)
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(case (pat-ctor Right _) true))))
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(fn map_right
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(doc "Apply f to the Right<a> payload; pass Left<e> through untouched.")
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(type
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(forall (vars e a b)
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(fn-type
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(params (fn-type (params a) (ret b))
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(con Either e a))
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(ret (con Either e b)))))
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(params f x)
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(body
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(match x
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(case (pat-ctor Right v)
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(term-ctor Either Right (app f v)))
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(case (pat-ctor Left l)
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(term-ctor Either Left l)))))
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(fn either
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(doc "Eliminator: apply on_left to a Left payload, on_right to a Right payload, fold both branches into the same result type c.")
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(type
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(forall (vars e a c)
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(fn-type
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(params (fn-type (params e) (ret c))
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(fn-type (params a) (ret c))
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(con Either e a))
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(ret c))))
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(params on_left on_right x)
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(body
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(match x
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(case (pat-ctor Left l) (app on_left l))
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(case (pat-ctor Right r) (app on_right r))))))
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@@ -0,0 +1 @@
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{"defs":[{"body":{"args":[{"name":"x","t":"var"},{"lit":{"kind":"int","value":1},"t":"lit"}],"fn":{"name":"+","t":"var"},"t":"app"},"doc":"Add 1 to an Int. Used as the function arg to map_right and either.","kind":"fn","name":"inc","params":["x"],"type":{"effects":[],"k":"fn","params":[{"k":"con","name":"Int"}],"ret":{"k":"con","name":"Int"}}},{"body":{"lhs":{"args":[{"args":[{"lit":{"kind":"int","value":0},"t":"lit"},{"args":[{"lit":{"kind":"int","value":42},"t":"lit"}],"ctor":"Right","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.from_right","t":"var"},"t":"app"}],"op":"io/print_int","t":"do"},"rhs":{"lhs":{"args":[{"args":[{"lit":{"kind":"int","value":99},"t":"lit"},{"args":[{"lit":{"kind":"int","value":7},"t":"lit"}],"ctor":"Left","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.from_right","t":"var"},"t":"app"}],"op":"io/print_int","t":"do"},"rhs":{"lhs":{"args":[{"args":[{"args":[{"lit":{"kind":"int","value":7},"t":"lit"}],"ctor":"Left","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.is_left","t":"var"},"t":"app"}],"op":"io/print_bool","t":"do"},"rhs":{"lhs":{"args":[{"args":[{"args":[{"lit":{"kind":"int","value":42},"t":"lit"}],"ctor":"Right","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.is_right","t":"var"},"t":"app"}],"op":"io/print_bool","t":"do"},"rhs":{"lhs":{"args":[{"args":[{"lit":{"kind":"int","value":0},"t":"lit"},{"args":[{"name":"inc","t":"var"},{"args":[{"lit":{"kind":"int","value":41},"t":"lit"}],"ctor":"Right","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.map_right","t":"var"},"t":"app"}],"fn":{"name":"std_either.from_right","t":"var"},"t":"app"}],"op":"io/print_int","t":"do"},"rhs":{"lhs":{"args":[{"args":[{"name":"inc","t":"var"},{"name":"inc","t":"var"},{"args":[{"lit":{"kind":"int","value":5},"t":"lit"}],"ctor":"Left","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.either","t":"var"},"t":"app"}],"op":"io/print_int","t":"do"},"rhs":{"args":[{"args":[{"name":"inc","t":"var"},{"name":"inc","t":"var"},{"args":[{"lit":{"kind":"int","value":100},"t":"lit"}],"ctor":"Right","t":"ctor","type":"std_either.Either"}],"fn":{"name":"std_either.either","t":"var"},"t":"app"}],"op":"io/print_int","t":"do"},"t":"seq"},"t":"seq"},"t":"seq"},"t":"seq"},"t":"seq"},"t":"seq"},"doc":"Drive each std_either combinator. Expected outputs (per line): 42, 99, true, true, 42, 6, 101.","kind":"fn","name":"main","params":[],"type":{"effects":["IO"],"k":"fn","params":[],"ret":{"k":"con","name":"Unit"}}}],"imports":[{"module":"std_either"}],"name":"std_either_demo","schema":"ailang/v0"}
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@@ -0,0 +1,31 @@
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; Iter 15d — third consumer demo.
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; Imports std_either, exercises all five combinators. First demo to
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; pass two function arguments to a single combinator (the eliminator
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; `either`); first to drive a 3-type-var polymorphic fn end-to-end.
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(module std_either_demo
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(import std_either)
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(fn inc
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(doc "Add 1 to an Int. Used as the function arg to map_right and either.")
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(type (fn-type (params (con Int)) (ret (con Int))))
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(params x)
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(body (app + x 1)))
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(fn main
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(doc "Drive each std_either combinator. Expected outputs (per line): 42, 99, true, true, 42, 6, 101.")
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(type (fn-type (params) (ret (con Unit)) (effects IO)))
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(params)
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(body
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(seq (do io/print_int (app std_either.from_right 0 (term-ctor std_either.Either Right 42)))
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(seq (do io/print_int (app std_either.from_right 99 (term-ctor std_either.Either Left 7)))
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(seq (do io/print_bool (app std_either.is_left (term-ctor std_either.Either Left 7)))
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(seq (do io/print_bool (app std_either.is_right (term-ctor std_either.Either Right 42)))
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(seq (do io/print_int (app std_either.from_right 0
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(app std_either.map_right inc
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(term-ctor std_either.Either Right 41))))
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(seq (do io/print_int (app std_either.either inc inc
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(term-ctor std_either.Either Left 5)))
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(do io/print_int (app std_either.either inc inc
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(term-ctor std_either.Either Right 100))))))))))))
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Reference in New Issue
Block a user