On Apr 4, 2007, at 5:01 PM, Edsko de Vries wrote:
Yeah, it's rather cool. IIRC, this style of encoding of recursion operators is attributed to Morris.
Do you have a reference?
Before the advent of equality coercions, GHC typically had problems generating code for these kinds of definitions. Did you test this with a release version? If so, how did you get around the code- generation problem? Is it the NOINLINE pragma that does the trick?
Yep. Without the NOINLINE pragma, ghc tries to inline the definition of fac, expanding it ad infinitum (this is a known bug in ghc and mentioned in the ghc manual). Hugs doesn't have a problem though.
I keep waiting for someone to use this fact to cook up a poor man's partial evaluation---use fix for static recursion, and ordinary recursive definitions for dynamic recursion. I fiddled with this a bit in the pH days (it had the same bug, for much the same reason). -Jan-Willem Maessen
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