Brummel
4683af6114
Desugar `Pattern::Lit` (top-level and nested in Ctor) to
`Term::If { cond = (== sv lit), then = body, else_ = fall_k }`.
After 16c, no Pattern::Lit survives the desugar pass; codegen
and typechecker never see one. `is_flat` reclassifies Lit as
non-flat to force the chain machinery; new `build_eq` helper
constructs the equality test per literal kind.
Tests: 99 → 103 (+1 e2e lit_pat_demo, +3 desugar unit). Demo
fixture exercises top-level lit arms (classify) and nested
lit-in-Ctor (categorize_first) with a local IntList; output
100/200/999/-1/0/7.
Known limitations documented in DESIGN.md and JOURNAL: (a)
chain machinery's Unit terminator means non-Wild-terminated
exhaustive matches with lit arms still need a trailing `_`
catch-all to type-check; (b) `==` is currently Int-only, so
Bool/Str/Unit lit patterns desugar correctly but error at
typecheck.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
53 lines
2.0 KiB
Plaintext
53 lines
2.0 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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; The trailing `_` catch-all in `categorize_first` is required by the
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; 16a chain machinery: the chain's terminator is a `Unit` literal,
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; reachable when no arm matches. A `_` arm dominates the chain so the
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; terminator stays unreachable in practice and the match type-checks.
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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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(case _ 0))))
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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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