[Haskell-beginners] Re: \x -> x < 0.5 && x > -0.5
Brent Yorgey
byorgey at seas.upenn.edu
Tue Oct 20 11:37:15 EDT 2009
On Tue, Oct 20, 2009 at 04:29:43PM +0100, Stephen Tetley wrote:
> Christian Maeder wrote:
>
> > Hoogle did not find a function of type:
> >
> > (b -> b -> b) -> (a -> b) -> (a -> b) -> a -> b
> >
> > or (b -> c -> d) -> (a -> b) -> (a -> c) -> a -> d
> >
> > But maybe such a function is worth being added to Data.Function.
>
> Hello Christian
>
> This is the big Phi or S' combinator. I would certainly second its
> addition to Data.Function.
>
> sprime p q r s = p (q s) (r s)
But this function already exists in the standard libraries: it is
called liftM2/liftA2, specialized to the ((->) e) monad/applicative
instance. This is what the rest of the thread has been talking about.
-Brent
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