Just to bring up some prior art, from what I've heard, F# calls this |>. In
Clojure the -> function takes a value and a series of functions, and
applies them in order from left to right, e.g. (-> 5 zero? not) ;;=> true.
Obviously, In OO languages, this is usually accomplished by chaining calls
foo.bar().baz().quux().
I agree that Haskell should provide this idiom. I find & to be a strange
name for it, but to be honest, it's no stranger than $ so I say go for it.
I would suggest | to mimic the unix pipe, but this obviously clashes with
Haskell guard syntax. I think |> is a reasonable name, but Data.Sequence
has already claimed it.
-- Dan Burton
On Tue, Nov 20, 2012 at 9:59 AM, Yitzchak Gale
It is a common idiom to write a sequence of composed combinators in reverse order to the way they would be written with ($) or (.). That naturally expresses the idea of the combinators as operations being applied in the given order.
This comes up so often, and is commonly used so many times in a single expression, that Control.Arrow.>>> is far too wordy, and even a two- character operator is awkward.
Surprisingly, until recently the operator (&) was still not used in any of the popular libraries, and its name naturally expresses the idea we
are
looking for. This operator has now been defined in the lens package. We hereby propose to move it to its natural home for more general use, Data.Function.
As in the lens package, we define the operator as a flipped version of ($), but with slightly higher precedence for better interaction with ($), and with left associativity. This definition has already proven useful and convenient even in the presence of the large and varied corpus of combinators and operators in the lens package. (There it was formerly known as (%), but that clashed with the usual meaning of (%) from Data.Ratio.)
infixl 1 & (&) :: a -> (a -> b) -> b a & f = f a {-# INLINE (&) #-}
Discussion period: 2 weeks
http://hackage.haskell.org/trac/ghc/ticket/7434
Thanks, Yitz
_______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries