[plt-scheme] Lazy Scheme praise and bug report

First, just want to say I've been playing with it and it's really cool. So  
thanks alot for that.

Second, the folds that lazy.ss provides seem to be a bit broken.  
Apparently when used it doesn't properly recursively force everything that  
need be forced, or something:

Welcome to DrScheme, version 350.
Language: Textual (MzScheme, includes R5RS).
> (require (lib "lazy.ss" "CSU660"))
> (define blah (foldl + 0 '(1 2 3 4)))
> blah
+: expects type <number> as 2nd argument, given: #<struct:promise>; other  
arguments were: 4