[Haskell] elementary tracing for Haskell

[Philip Wadler]

Are there any tools for beginning programmers that give traces of 
Haskell programs?  I want something like the following.  Given the 
defintion

        sum [] = 0
        sum (x:xs) = x + sum xs
typing
        sum [1,2,3]
should yield this trace
        sum [1,2,3]
        1 + sum [2,3]
        1 + 2 + sum [3]
        1 + 2 + 3 + sum []
        1 + 2 + 3 + 0
        1 + 2 + 3
        1 + 5
        6
I know there are advanced tools like Hat, but (unless I'm missing 
something) they don't yield anything as naive as the above, and it's 
naive users I'm trying to help here.  -- P

PS.  Google search on "Haskell trace" yields lots on Hat, plus the 
following.

The Mystery of Brigadier General Harry L. Haskell
... we have developed a short biography of General Haskell and been 
able to trace the
 locations where he lived, and, possibly, how the medal came into my 
family. ...
 family.phelpsinc.com/branches/haskell/ - 28k - Cached - Similar pages

Philip Wadler, Professor of Theoretical Computer Science
School of Informatics, University of Edinburgh
JCMB, Mayfield Road, Edinburgh EH9 3JZ SCOTLAND
+44 131 650 5174 http://homepages.inf.ed.ac.uk/wadler/
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