"Yu-Teh Shen"
I got question about why haskell insist to be a purely FL. I mean is there any feature which is only support by pure? I mean maybe the program is much easier to prove? Or maybe we can cache some value for laziness. Could anyone give me some more information about why haskell needs to be pure.
To give a short answer: Because if pureness would be abandoned for easy implementation of feature X, features Y and Z would become completely awkward. The pureness is an ideological design decision basing on the assumption that pureness is ideal to ensure whole-system consistency. Most important is referential transparency, its lack of spooky side-effects and thus making global memoization of evaluation results feasible. In fact, the most obvious point really seems to be that getChar :: Char cant' be cached, though its type implies it, while getChar :: IO Char enshures that only the _action_ of getting a char can be cached, not the char itself. (and asking why and how the IO type does that opens a big can of worms) It's along the lines of "a value is an unary, static function that returns a value" vs. "an input function is an unary, dynamic function that returns a value" and the proper handling of the terms "static" and "dynamic" in every possible case. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.