Brummel
ca30606aec
Adds path-2 from the 16b.2 planning entry. Desugar now defers
LetRecs whose captures include Term::Let-bound names; a new
ailang-check::lift_letrecs pass runs after typecheck and uses the
elaborated env to resolve capture types. ailang-check learns a real
Term::LetRec typing rule in synth and verify_tail_positions.
- desugar: Term::LetRec arm gains a defer-arm; helpers promoted to
pub for reuse by the lift pass; find_non_callee_use moved before
classification.
- ailang-check::synth/verify_tail_positions: real LetRec rules
(effect-subset, locals install, recursive name in body+in_term).
- ailang-check::lift.rs (new, 720 LOC): post-typecheck lift with
post-order traversal, env-walk for capture-type resolution,
fast-path skip when no LetRec is present.
- ail::main.rs: build path now does load → check → desugar →
lift_letrecs → codegen.
- examples/local_rec_let_capture.{ailx,ail.json}: new fixture
capturing a let-bound `threshold` in a recursive helper.
- e2e + check unit tests: 106 → 110 (+4).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
49 lines
2.0 KiB
Plaintext
49 lines
2.0 KiB
Plaintext
; Iter 16b.3 — LetRec captures of `Term::Let`-bound names.
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; `count_below(n)` returns how many integers in 1..=n are strictly
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; less than a `threshold` computed locally from `n`. The recursive
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; helper `loop` captures the let-bound name `threshold` from the
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; enclosing scope; its type is only known after typecheck (the
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; let-value is `(app + 5 5)` — an `Int` expression, but the desugar
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; pass cannot resolve that without inference).
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;
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; The 16b.2 desugar pass cannot lift this LetRec (capture is Let-bound,
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; not fn-param). Instead the desugar pass leaves the LetRec in place;
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; the post-typecheck `lift_letrecs` pass in `ailang-check` resolves
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; `threshold`'s type as `Int` from the typechecker's env and produces
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; a synthetic top-level fn `loop$lr_0(i: Int, n: Int, threshold: Int)
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; -> Int`, rewriting every `(app loop ARGS)` to `(app loop$lr_0 ARGS n
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; threshold)`.
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;
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; Expected stdout (one per line):
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; count_below(0) = 0 (empty range; loop's first call has i > n)
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; count_below(5) = 5 (1..=5; threshold = 10; all 5 are < 10)
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; count_below(15) = 9 (1..=15; threshold = 10; 1..=9 are < 10)
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(module local_rec_let_capture
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(fn count_below
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(doc "Count i in 1..=n with i < threshold, where threshold = 5+5.")
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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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(let threshold (app + 5 5)
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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 0, 5, 15. Expected (per line): 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 0))
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(seq (do io/print_int (app count_below 5))
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(do io/print_int (app count_below 15)))))))
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