In lambda calculus you can take a beta reduction as the step.
But Haskell is not normally implemented by lambda calculus so you have to pick something else.
There are measures of reduction that you can come up with but they will vary, e.g., by compiler, optimization level, etc.
I think time is a much more interesting measure, since that's what you really care about in the end.

On Jan 14, 2008 2:03 PM, Ben Franksen < ben.franksen@online.de> wrote:
Lennart Augustsson wrote:
> What is a reduction anyway?

I am not an expert but I thought in lambda calculus one has primitive rules
for evaluation, e.g. beta reduction. So a reduction is a 'smallest step' in
reducing an expression to normal form, no?

Cheers
Ben

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