[Haskell-cafe] Re: about Haskell code written to be "too smart"

John Lato wrote:

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From: wren ng thornton Dan Weston wrote:

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So to be clear with the terminology:

inductive = good consumer? coinductive = good producer?

So fusion should be possible (automatically? or do I need a GHC rule?) with inductive . coinductive

Or have I bungled it?

Not quite. Induction means starting from base cases and building things upwards from those. Coinduction is the dual and can be thought of as starting from the ceiling and building your way downwards (until you hit the base cases, or possibly forever).

( quite a lot of text trimmed for brevity)

Wren, thank you for contributing this post. Coming from the point of view of someone who doesn't grok it all yet, this is the best commentary I've read on deforestation/fusion, and in fact is helpful for category theory newbies as well (at least I found it so). It really should go on a wiki somewhere.

If you haven't read Rewriting Haskell Strings[1] yet, it's an excellent paper. There are a number of other canonical fusion papers, but RHS has the best introduction I've seen and it goes into both the build/fold and unfold/destroy styles. It doesn't have much on the category theory and recursion theory side of things though. [1] http://www.cse.unsw.edu.au/~dons/papers/CSL06.html -- Live well, ~wren