On Wednesday 07 December 2005 20:19, you wrote:
On Wed, Dec 07, 2005 at 07:47:46PM +0000, Robin Green wrote:
Some day you may thank for this verbosity, because it encourages you do program in a purely functional way making your program more friendly for SMP execution.
You are mistaken. The verbosity is necessary if you want "visual" referential transparency, but not necessary if you only want pure functional programming. Only the latter is helpful for optimisability. I am hoping to write a paper on this topic.
I am afraid I don't understand.
Let's say you want to write a function seqPair :: (Monad m) => (m a, m b) -> m (a, b) which returns a computation which does the left computation followed by the right computation (i.e. it's like the sequence function, but for pairs instead of lists). In Haskell you could write this as: seqPair mx my = do x <- mx y <- my return (x, y) However, wouldn't it be nice if we could write something like (warning: hypothetical syntax) seqPair $= (,) or (the slightly less cryptic version) seqPair x y $= (x, y) This is not referentially transparent because it is not equivalent to seqPair x y $= swap (y, x) where swap (a, b) = (b, a) (can you see why not?) But it _is_ semantically equivalent to the first definition I gave, which is functionally pure, so it is also functionally pure (at least, when you consider it as a "black box"). -- Robin