Definition of 'let' declarations, from HOL

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ZF/Let.ML	Fri Apr 14 12:03:15 1995 +0200
@@ -0,0 +1,14 @@
+(*  Title: 	ZF/Let
+    ID:         $Id$
+    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1995  University of Cambridge
+
+Let expressions -- borrowed from HOL
+*)
+
+open Let;
+
+val [prem] = goalw thy
+    [Let_def] "(!!x. x=t ==> P(u(x))) ==> P(let x=t in u(x))";
+br (refl RS prem) 1;
+qed "letI";

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ZF/Let.thy	Fri Apr 14 12:03:15 1995 +0200
@@ -0,0 +1,30 @@
+(*  Title: 	ZF/Let
+    ID:         $Id$
+    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1995  University of Cambridge
+
+Let expressions -- borrowed from HOL
+*)
+
+Let = ZF +
+
+types
+  letbinds  letbind
+
+consts
+  Let           :: "['a, 'a => 'b] => 'b"
+
+syntax
+  "_bind"       :: "[idt, 'a] => letbind"             ("(2_ =/ _)" 10)
+  ""            :: "letbind => letbinds"              ("_")
+  "_binds"      :: "[letbind, letbinds] => letbinds"  ("_;/ _")
+  "_Let"        :: "[letbinds, 'a] => 'a"             ("(let (_)/ in (_))" 10)
+
+translations
+  "_Let(_binds(b, bs), e)"  == "_Let(b, _Let(bs, e))"
+  "let x = a in e"          == "Let(a, %x. e)"
+
+defs
+  Let_def       "Let(s, f) == f(s)"
+
+end