On Tuesday 22 April 2008, Simon Marlow wrote: > I'm hoping someone will supply some. There seemed to be strong opinion > on #haskell that this change should be made, but it might just have been > a very vocal minority.
These are the arguments off the top of my head: 1) Anything of the form: f $ g $ h $ x with right associative ($) can instead be written: f . g . h $ x where the associativity of ($) doesn't matter. It's not uncommon to want to peel off the end of such a pipeline to eliminate a point. For the second form, such a translation is: \x -> f . g . h $ x ==> f . g . h However: \x -> f $ g $ h $ x ==> f $ g $ h Is invalid, so one might argue that writing such pipelines with composition is a better habit to get into, as it allows easier cleanup of code in this way (if you like somewhat point-free code, that is). 2) Left associative ($) allows you to eliminate more parentheses. Per #1, any parentheses eliminated by right associative ($) can be eliminated by (.) and a single ($). However, left associative ($) allows, for instance: f (g x) (h y) ==> f $ g x $ h y 3) Left associative ($) is consistent with left associative ($!). The right associative version of the latter is inconvenient, because it only allows things to be (easily) strictly applied to the last argument of a function. Needing to strictly apply to other arguments gives rise to things like: (f $! x) y z ((f $! x) $! y) $! z Left associative, these are: f $! x $ y $ z f $! x $! y $! z There may be more arguments, but those are the ones I've heard that I can think of at the moment. #3 strikes me as the most likely to bite people (the other two are more stylistic issues), but I suppose I don't know the relative frequency of strict pipelines (f $! g $! x) versus strict applications at non-final arguments. And I suppose one has to weigh these arguments against breaking lots of code. Cheers, -- Dan _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime