(* 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 * typ * nat)maybe"
(* type inference algorithm W *)
consts
W :: [expr, typ list, nat] => result_W
primrec W expr
"W (Var i) a n = (if i < length a then Ok(id_subst, nth i a, n)
else Fail)"
"W (Abs e) a n = ( (s,t,m) := W e ((TVar n)#a) (Suc n);
Ok(s, (s n) -> t, m) )"
"W (App e1 e2) a n =
( (s1,t1,m1) := W e1 a n;
(s2,t2,m2) := W e2 ($s1 a) m1;
u := mgu ($s2 t1) (t2 -> (TVar m2));
Ok( $u o $s2 o s1, $u (TVar m2), Suc m2) )"
end