Steve Schafer wrote:
Here's the essence of the problem. If I have this:
process1 x y = let u = foo x y; v = bar u; w = baz v in w
I can easily rewrite it in point-free style:
process1 = baz . bar . foo
Not unless you have a much fancier version of function composition, like... http://okmij.org/ftp/Haskell/types.html#polyvar-comp
But if I have this:
process2 x y = let u = foo x y; v = bar u; w = baz v u in w
then I can't avoid naming and using an intermediate variable. And that annoys me. The u in process2 is of no more value to me (pardon the pun) as the one in process1, but I am forced to use it simply because the data flow is no longer strictly linear.
The reason I brought up monads as a possible means of managing this problem is that the State, Reader and Writer monads already handle certain specific "shapes" of nonlinear data flow, which suggested to me that maybe there was a monadic approach to managing nonlinear data flow in a more general way. Of course, if there is a non-monadic, purely functional way to do it, that would be even better, but I've never seen such a thing (short of doing lots of tupling and un-tupling).
-- Use combinators which automate the tupling/un-tupling. -- See also, the Joy language... -- http://www.latrobe.edu.au/philosophy/phimvt/joy/j00rat.html main = process2 test process2 = baz . bar . dup . foo foo = mul . (push 2) . mul bar = rep . swap . (push 'A') baz = add . len test = (2,(3,()))::(Int,(Int,())) dup (a,b) = (a,(a,b)) swap (a,(b,c)) = (b,(a,c)) push a b = (a,b) lift1 f (a,b) = (f a,b) lift2 f (a,(b,c)) = (f a b,c) len = lift1 length add = lift2 (+) mul = lift2 (*) rep = lift2 replicate