Brummel
c0668178bb
Flips the desugar's MatchArm-capture rejection from panic to defer.
The 16b.3 lift_letrecs pass already handled match-arm bindings via
type_check_pattern_for_lift (Pattern::Var, Pattern::Ctor with sub-
patterns, ctor-field substitution against scrutinee args), so this
iter is a single-line classification change in desugar plus the
fixture and tests that exercise it.
- desugar.rs: MatchArm classification now defers (same arm as
LetBound); EnclosingLetRec panic remains for 16b.7.
- examples/local_rec_match_capture.{ailx,ail.json}: enclosing fn
pattern-matches on Pair<Int,Int>, inner LetRec captures both
match-arm bindings simultaneously. Lifts to
loop$lr_0(i: Int, threshold: Int, n: Int) -> Int.
- e2e + check + desugar tests: 110 → 113 (+3).
First fixture lifting more than one capture; subst_call_with_extras
already handled it generically.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
60 lines
2.5 KiB
Plaintext
60 lines
2.5 KiB
Plaintext
; Iter 16b.4 — LetRec captures of match-arm pattern bindings.
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; `count_below(p)` takes a `Pair Int Int` (threshold, n), pattern-
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; matches on `(MkPair threshold n)`, and inside that match arm runs
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; a recursive helper `loop` that captures BOTH match-arm bindings
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; (`threshold` and `n`) and counts how many integers in 1..=n are
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; strictly less than `threshold`.
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;
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; The 16b.2/16b.3 desugar passes cannot lift this LetRec — both
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; `threshold` and `n` are bound by a `Pattern::Ctor` Var sub-
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; pattern (`ScopeEntry::MatchArm`). Before 16b.4 this panicked at
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; desugar time. Now the desugar pass leaves the LetRec in place;
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; the post-typecheck `lift_letrecs` pass walks the enclosing match,
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; resolves each pattern binding's type via constructor-field
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; substitution against the matched ctor's declared field types
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; (here: `Pair Int Int`'s ctor `MkPair` has fields `[Int, Int]`,
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; and the scrutinee's `Type::Con.args` are also `[Int, Int]`, so
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; substitution is a no-op and both bindings get type `Int`), and
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; lifts to `loop$lr_0(i: Int, threshold: Int, n: Int) -> Int`.
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;
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; The match has a single ctor and no catch-all; the chain machinery
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; treats the only arm as default-dominating since there's no `_`
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; arm needed for an exhaustive single-ctor ADT (Pair has one ctor).
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;
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; Expected stdout (one per line):
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; count_below(MkPair 10 0) = 0
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; count_below(MkPair 10 5) = 5 (1..=5 all below 10)
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; count_below(MkPair 10 15) = 9 (1..=9 below 10, 10..=15 not)
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(module local_rec_match_capture
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(data Pair (vars a b)
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(ctor MkPair a b))
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(fn count_below
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(doc "Match-arm captures `threshold` and `n`; inner LetRec captures both.")
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(type (fn-type (params (con Pair (con Int) (con Int))) (ret (con Int))))
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(params p)
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(body
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(match p
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(case (pat-ctor MkPair threshold n)
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(let-rec loop
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(params i)
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(type (fn-type (params (con Int)) (ret (con Int))))
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(body
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(if (app > i n)
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0
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(if (app < i threshold)
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(app + 1 (app loop (app + i 1)))
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(app loop (app + i 1)))))
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(in (app loop 1)))))))
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(fn main
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(doc "Drive count_below at MkPair 10 {0,5,15}. Expected: 0, 5, 9.")
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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 count_below (term-ctor Pair MkPair 10 0)))
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(seq (do io/print_int (app count_below (term-ctor Pair MkPair 10 5)))
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(do io/print_int (app count_below (term-ctor Pair MkPair 10 15))))))))
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