jamie.love:
  

   Ah, of course.

   Thanks. I removed the hPut and it runs smoothly.  I had forgotten that
   haskell chooses the types dynamically.

   Shouldn't haskell pick up that there is no 'mod' for Word8?  I mean,
   shouldn't I get a nicer error message?
    

Well, it inferred Word8 for your generated values, so 256 overflowed to 0.
Stating the expected type here would prevent that. (And is why mandatory 
top level declarations are good -- they can prevent bugs caused by 
an unexpected type being inferred).


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Jamie Love
Senior Consultant
Aviarc Australia
Mobile: +61 400 548 048