Re: [jhc] Loops.

On Thu, Mar 20, 2008 at 12:51:20PM -0500, Samuel Bronson wrote:

On 3/20/08, John Meacham wrote:

...

in core, so it is not recognized as a loop. I doubt it will be much of a problem in practice, and eta reduction is an anti-optimization in general.

Why isn't that recognized as a loop? Isn't it typically beneficial in the body of a function to replace calls like that with the return value? For example:

fix :: (a -> a) -> a fix f = f (fix f)

Oh, it is recognized as recursive*, but not as an infinite loop. When the jhc optimizer comes across something it knows is equivalent to bottom, it replaces it with 'error "<<loop>>"'. ghc does the same thing. it is this replacement that jhc wasn't doing, which is okay since the replacement is really just an optimization jhc will take advantage of when it can find, but doesn't look to hard for. (though, other optimizations likely expose more 'manifest loops'. * though the fact jhc is blowing stack means that perhaps there is a bug whereby it isn't being recognized as recursive. -- John Meacham - ⑆repetae.net⑆john⑈