Brummel
af35612c1d
Eliminates the Unit-typed chain default that 16c left in place.
Adds __unreachable__ : forall a. a — codegen lowers to LLVM
unreachable. The 16a/16c chain machinery now uses it as the
deepest fall-through, so exhaustive matches with non-Unit arms
no longer need a (case _ ...) workaround.
- check/builtins.rs: register __unreachable__ as Forall(a, a).
- codegen: Term::Var "__unreachable__" emits LLVM unreachable
and sets block_terminated; If/Match/fn-body gate downstream
work on that flag.
- desugar: chain default switched from Lit{Unit} to Var.
- examples/lit_pat: categorize_first's trailing _ arm removed.
Hash changes from c4faec3abc2ed388 to 644de0c0ec15fc17.
- examples/unreachable_demo: positive fixture using safe_div
with __unreachable__ in the impossible branch.
- e2e + desugar tests: 122 → 124 (+2).
Path-a from 16b.2 planning: real primitive over a desugar-time
exhaustiveness pre-check (which would need cross-module type
registry access from desugar).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
55 lines
2.1 KiB
Plaintext
55 lines
2.1 KiB
Plaintext
; Iter 16c — lit patterns at top level and inside Ctor sub-patterns.
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; `classify` matches an Int against three lit arms (0, 1, default).
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; `categorize_first` matches a List<Int>: empty -> -1, head==0 -> 0,
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; otherwise the head value. The latter exercises Pat-Lit nested
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; inside Pat-Ctor's first field. Both shapes are now handled by the
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; 16c desugar pass; codegen sees only If/Match-on-Ctor combinations.
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;
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; Iter 16d update — the chain machinery's terminator is now the
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; polymorphic `__unreachable__` builtin (`forall a. a`, lowered to
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; LLVM `unreachable`) instead of a `Unit` literal. That removed the
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; pre-16d need for a trailing `(case _ 0)` arm in `categorize_first`
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; whose only purpose was to dominate the synthetic `Unit`-typed
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; terminator. The two ctor arms (`Nil` and `Cons h _`) are
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; exhaustive on `IntList`; the chain default is never reached.
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;
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; Expected stdout (one per line): 100, 200, 999, -1, 0, 7.
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(module lit_pat
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(data IntList
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(ctor Nil)
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(ctor Cons (con Int) (con IntList)))
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(fn classify
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(doc "Map 0->100, 1->200, anything else->999.")
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(type (fn-type (params (con Int)) (ret (con Int))))
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(params n)
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(body
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(match n
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(case (pat-lit 0) 100)
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(case (pat-lit 1) 200)
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(case _ 999))))
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(fn categorize_first
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(doc "Empty -> -1; first element 0 -> 0; otherwise return the head.")
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(type (fn-type (params (con IntList)) (ret (con Int))))
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(params xs)
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(body
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(match xs
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(case (pat-ctor Nil) -1)
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(case (pat-ctor Cons (pat-lit 0) _) 0)
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(case (pat-ctor Cons h _) h))))
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(fn main
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(doc "Drive both fns. Expected (per line): 100, 200, 999, -1, 0, 7.")
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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 classify 0))
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(seq (do io/print_int (app classify 1))
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(seq (do io/print_int (app classify 17))
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(seq (do io/print_int (app categorize_first (term-ctor IntList Nil)))
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(seq (do io/print_int (app categorize_first (term-ctor IntList Cons 0 (term-ctor IntList Nil))))
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(do io/print_int (app categorize_first (term-ctor IntList Cons 7 (term-ctor IntList Nil))))))))))))
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