On Feb 6, 2006, at 9:19 AM, Bulat Ziganshin wrote:
Hello Ketil,
Monday, February 06, 2006, 4:06:35 PM, you wrote:
foo :: !Int -> !Int
KM> (Is the second ! actually meaningful?)
yes! it means that the function is strict in its result - i.e. can't return undefined value when strict arguments are given. this sort of knowledge should help a compiler to "propagate" strictness and figure out the parts of program that can be compiled as strict code. really, i think ghc is able to figure functions with strict result just like it is able to figure strict function arguments
KM> Personally, I think is much nicer than sprinkling seq's around, and KM> generally sufficient. However, there could perhaps be disambiguities?
btw, it's just implemented in the GHC HEAD
Actually, I think strict _patterns_ are implemented. You are talking about strict _type annotations_, which is rather different. As I understand it, strict patterns are just sugar for putting 'seq' in the right places. There has been some work dealing with folding strictness and totality information into types systems; I find the resulting type systems pretty ugly, and I think they'd be pretty hard to bolt onto an HM base. Robert Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG