Re: Proposal: Add (&) to Data.Function

$. is kind of the worst of all possible worlds to me. (|>) at least has the ML precedent going for it, but ($.) using the . to indicate the side that the function is on offers very little to visually distinguish it from ($) and no such precedent to motivate it. The first time I read your post I read the . as the end of sentence marker. =P -Edward On Tue, Nov 20, 2012 at 4:08 PM, Gábor Lehel wrote:

Another option that was raised in a mailing list thread at some point (I think it was one about records): $.

The idea being to evoke the dot operator of object-oriented languages together with the existing ($) of function application.

theList $. filter even $. map (*2) $. sum

If you read it by focusing on the dots as in an OO language it sort of works. Not sure how I feel about it, throwing it out there. As a candidate for the least bad choice I think it at least qualifies.

On Tue, Nov 20, 2012 at 5:59 PM, Yitzchak Gale wrote:

...

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

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