# Proposal: Add (&) to Data.Function

Twan van Laarhoven twanvl at gmail.com
Wed Nov 21 13:55:05 CET 2012

```+1 for (&) or (#),

-1 for (|>), because that name strongly suggests that there is also an (<|)
operator. Of course we could add (<|) as a synonym for (\$), but that would be
unnecessary and confusing.

Twan

On 20/11/12 17:59, 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
>
>
> Thanks,
> Yitz
>
>
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