; Iter 16c — lit patterns at top level and inside Ctor sub-patterns.
; `classify` matches an Int against three lit arms (0, 1, default).
; `categorize_first` matches a List<Int>: empty -> -1, head==0 -> 0,
; otherwise the head value. The latter exercises Pat-Lit nested
; inside Pat-Ctor's first field. Both shapes are now handled by the
; 16c desugar pass; codegen sees only If/Match-on-Ctor combinations.
;
; Iter 16d update — the chain machinery's terminator is now the
; polymorphic `__unreachable__` builtin (`forall a. a`, lowered to
; LLVM `unreachable`) instead of a `Unit` literal. That removed the
; pre-16d need for a trailing `(case _ 0)` arm in `categorize_first`
; whose only purpose was to dominate the synthetic `Unit`-typed
; terminator. The two ctor arms (`Nil` and `Cons h _`) are
; exhaustive on `IntList`; the chain default is never reached.
;
; Expected stdout (one per line): 100, 200, 999, -1, 0, 7.

(module lit_pat

  (data IntList
    (ctor Nil)
    (ctor Cons (con Int) (con IntList)))

  (fn classify
    (doc "Map 0->100, 1->200, anything else->999.")
    (type (fn-type (params (con Int)) (ret (con Int))))
    (params n)
    (body
      (match n
        (case (pat-lit 0) 100)
        (case (pat-lit 1) 200)
        (case _ 999))))

  (fn categorize_first
    (doc "Empty -> -1; first element 0 -> 0; otherwise return the head.")
    (type (fn-type (params (con IntList)) (ret (con Int))))
    (params xs)
    (body
      (match xs
        (case (pat-ctor Nil) -1)
        (case (pat-ctor Cons (pat-lit 0) _) 0)
        (case (pat-ctor Cons h _) h))))

  (fn main
    (doc "Drive both fns. Expected (per line): 100, 200, 999, -1, 0, 7.")
    (type (fn-type (params) (ret (con Unit)) (effects IO)))
    (params)
    (body
      (seq (app print (app classify 0))
      (seq (app print (app classify 1))
      (seq (app print (app classify 17))
      (seq (app print (app categorize_first (term-ctor IntList Nil)))
      (seq (app print (app categorize_first (term-ctor IntList Cons 0 (term-ctor IntList Nil))))
           (app print (app categorize_first (term-ctor IntList Cons 7 (term-ctor IntList Nil))))))))))))