On Thu, Feb 5, 2009 at 11:12 AM, Andrew Wagner
Are you saying that using equations to add a level of indirection prevents optimization? I still don't see it - discarding x doesn't change the semantics, so a good compiler /should/ do this. How is this different from optimizing out application of a constant function?
No, no compiler should change "getChar >>= \x -> getChar" to just getChar, because it's just wrong. The first will try to read in two values of type Char, the second will only try to read one. Side effects aren't THAT hated!
Right, but that's only because the compiler either somehow knows about side effects or there is some other mechanism - e.g. an implicit World token that gets passed around - that prevents optiimization. As far as the formal semantics of the language are concerned, there's no essential difference between "getChar >>= \x -> getChar" and " Foo 3
= \x -> Foo 7 " for some data constructor Foo. I should think the latter would be optimized; if so, why not the former? The presence of some hidden (from me, anyway) semantics is inescapable.
-g