Variables(should actually call them constants) within the while loop should be scoped or it will have a random behaviour! This should at least be mentioned in the documentation, and it might be good to add a warning of sorts!

Look at the following code:

rules(lex-to-dr-Count := 0)
; number := 0
; while( not(<eq> (number,<lex-to-dr-Count>)),
       <debug> "a";lex-to-dr-Count;debug
  	;	x := <build-xeger> sort(s)
  	;	<debug> "b"
	;	dr := <generate-terminals> x
	;	<debug> "c"
	;	newCount := <addi> (<lex-to-dr-Count>,1)
	;	<debug> "d"
	;	rules( 	Terminals :+ s -> dr
	 			lex-to-dr-Count:= newCount )
	;	<debug> "e"
	)

Executing this a couple of times yielded results such as(,’s replacing newline):
a, 0, b, c, d, e, a, 1, a, 0, b, c, d, e, a, 1, b, a, 0, b, c, d, e, a, 1, b, a, 0, b …

This is probably due to the fact that in stratego you can not rewrite a variable(constant). Normally this yields warnings, but it doesnt with a while loop, since the constant is only physically written down once, but it is very probable the assignment will occur more than once, otherwise you wouldnt use a while loop.

Scoping these variables solves the problem.

To avoid people from running head first into walls, it might be a good idea to either add a warning to the observer for this or at least add a small note in the stratego documentation of while and probably repeat aswell?

Submitted by André Vieira on 3 January 2012 at 16:18