src/HOL/Option.ML

+(*  Title:      Option.ML
+    ID:         $Id$
+    Author:     Tobias Nipkow
+    Copyright   1996  TU Muenchen
+
+Derived rules
+*)
+
+open Option;
+
+val [prem] = goal Option.thy "P(opt) ==> P(None) | (? x. P(Some(x)))";
+ br (prem RS rev_mp) 1;
+ by (option.induct_tac "opt" 1);
+ by (ALLGOALS(Fast_tac));
+bind_thm("optionE", standard(result() RS disjE));
+(*
+goal Option.thy "opt=None | (? x.opt=Some(x))"; 
+by (option.induct_tac "opt" 1);
+by (Simp_tac 1);
+by (rtac disjI2 1);
+by (rtac exI 1);
+by (Asm_full_simp_tac 1);
+qed"option_cases";
+*)
+goal Option.thy "P(case opt of None => a | Some(x) => b(x)) = \
+\                ((opt = None --> P a) & (!x. opt = Some x --> P(b(x))))";
+by (option.induct_tac "opt" 1);
+by (Simp_tac 1);
+by (Asm_full_simp_tac 1);
+by(Fast_tac 1);
+qed"expand_option_case";