[Haskell-cafe] Is there a tool to see reduction steps?

I have been given a piece of code that uses Tie-ing the Knot concept to label a tree of nodes in breath first manner. It seems to work fine, but I am having trouble expanding the code on my own to see the evaluation process. I like to know if there is a tools to use to see the reduction steps.

data Tree = Leaf | Node Tree Int Tree deriving Show

label (Node ln _ rn) ((h:r):rest) = (Node lr h rr, r:r2) where (lr, r1) = label ln rest (rr, r2) = label rn r1 label _ _ = (Leaf, []) lt t = let (r, unused) = label t ([1..]:unused) in r

-- Daryoush Weblog: http://onfp.blogspot.com/