(* Title: HOL/MiniML/W.thy
ID: $Id$
Author: Dieter Nazareth and Tobias Nipkow
Copyright 1995 TU Muenchen
Type inference algorithm W
*)
W = MiniML +
types
result_W = "(subst * type_expr * nat)maybe"
(* type inference algorithm W *)
consts
W :: [expr, type_expr list, nat] => result_W
primrec W expr
W_Var "W (Var i) a n = (if i < length a then Ok(id_subst, nth i a, n)
else Fail)"
W_Abs "W (Abs e) a n = W e ((TVar n)#a) (Suc n) bind
(%(s,t,m). Ok(s, Fun (s n) t, m) )"
W_App "W (App e1 e2) a n =
W e1 a n bind
(%(s1,t1,m1). W e2 ($ s1 a) m1 bind
(%(s2,t2,m2). mgu ($ s2 t1) (Fun t2 (TVar m2)) bind
(%u. Ok( ($ u) o (($ s2) o s1), $ u (TVar m2), Suc m2) )))"
end