--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Concurrent/single_assignment_sequential.ML Sat Feb 06 22:01:48 2010 +0100
@@ -0,0 +1,30 @@
+(* Title: Pure/Concurrent/single_assignment_sequential.ML
+ Author: Makarius
+
+Single-assignment variables (sequential version).
+*)
+
+structure Single_Assignment: SINGLE_ASSIGNMENT =
+struct
+
+abstype 'a var = Var of 'a SingleAssignment.saref
+with
+
+fun var _ = Var (SingleAssignment.saref ());
+
+fun peek (Var var) = SingleAssignment.savalue var;
+
+fun await v =
+ (case peek v of
+ SOME x => x
+ | NONE => Thread.unavailable ());
+
+fun assign (v as Var var) x =
+ (case peek v of
+ SOME _ => raise Fail "Duplicate assignment to variable"
+ | NONE => SingleAssignment.saset (var, x));
+
+end;
+
+end;
+