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

wren ng thornton wren at freegeek.org
Thu Mar 26 20:40:50 EDT 2009

John Lato wrote:
> > From: wren ng thornton <wren at freegeek.org>
> > Dan Weston wrote:
> > > 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,

More information about the Haskell-Cafe mailing list