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src/HOL/W0/Maybe.ML
author nipkow
Mon, 09 Feb 1998 14:40:59 +0100
changeset 4612 26764de50c74
parent 4089 96fba19bcbe2
child 4831 dae4d63a1318
permissions -rw-r--r--
Used THEN_ALL_NEW.

(* Title:     HOL/W0/Maybe.ML
   ID:        $Id$
   Author:    Dieter Nazareth and Tobias Nipkow
   Copyright  1995 TU Muenchen
*)


(* constructor laws for bind *)
goalw thy [bind_def] "(Ok s) bind f = (f s)";
by (Simp_tac 1);
qed "bind_Ok";

goalw thy [bind_def] "Fail bind f = Fail";
by (Simp_tac 1);
qed "bind_Fail";

Addsimps [bind_Ok,bind_Fail];

(* expansion of bind *)
goal thy
  "P(res bind f) = ((res = Fail --> P Fail) & (!s. res = Ok s --> P(f s)))";
by (maybe.induct_tac "res" 1);
by (fast_tac (HOL_cs addss simpset()) 1);
by (Asm_simp_tac 1);
qed "expand_bind";

goal Maybe.thy
  "((m bind f) = Fail) = ((m=Fail) | (? p. m = Ok p & f p = Fail))";
by (simp_tac (simpset() addsplits [expand_bind]) 1);
qed "bind_eq_Fail";

Addsimps [bind_eq_Fail];
isabelle