[Haskell-beginners] Still confused

[Brandon Allbery]

On Mon, Jul 1, 2013 at 2:03 PM, Marc Gorenstein
<marc.gorenstein at gmail.com>wrote:

> Here are two examples of operator sections. The first takes the infix
> operator
> / and turns it into a prefix operator.
>
> Prelude> let eight_div_by = ((/) 8 )
> Prelude> eight_div_by 4
> 2.0
>

Yes. A section is just this conversion of an infix operator to a prefix
function, but with one parameter carried along with it. You can supply it
on either side as appropriate; (/ 8) is the same as (\x -> x / 8) which in
turn is the same as (\x -> (/) x 8), whereas (8 /) is (\x -> 8 / x) is (\x
-> (/) 8 x). Note that it must be *inside* the parentheses to be a section;
if it's outside, then it's a normal function (not operator!) parameter.

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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