Infix expressions
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WORK IN PROGRESS From: dons@cse.unsw.edu.au (Donald Bruce Stewart) To: Simon Peyton-Jones <simonpj@microsoft.com> Date: Wed, 15 Mar 2006 23:25:34 +1100 Cc: haskell-prime@haskell.org, oleg@pobox.com Subject: Re: Infix expressions simonpj: > I often wish that cool tricks like this could be collected on the > Haskell web site. Now that it's a wiki, anyone could do that. Yes, this is _exactly_ the kind of thing to add to the Idioms page of the wiki, here: http://www.haskell.org/haskellwiki/Category:Idioms So if anyone knows of an interesting Haskell trick, and wants to write about it, add a page! We should take advantage of the fact we have a lot of good authors in the community to document all the interesting things that we come up with -- Don > > Simon > > | -----Original Message----- > | From: haskell-prime-bounces@haskell.org > [mailto:haskell-prime-bounces@haskell.org] On Behalf Of > | oleg@pobox.com > | Sent: 15 March 2006 04:34 > | To: doaitse@cs.uu.nl; haskell-prime@haskell.org > | Subject: Infix expressions > | > | > | Doaitse Swierstra wrote: > | > In Haskell we write `f` in order to infixify the identifier f. In > ABC > | > the stuff between backquotes is not limited to an identifier, but > any > | > expression may occur there. This would allow one to write e.g. > | > > | > xs `zipWith (+)` ys > | > | Chung-chieh Shan and Dylan Thurston showed the Haskell98 solution for > | exactly the same example, in their article `Infix expressions', > | back in 2002: > | > http://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html > | > | For ease of reference, here's their elegant solution: > | > | > infixr 0 -:, :- > | > data Infix f y = f :- y > | > x -:f:- y = x `f` y > | > > | > main = print $ [1,2,3] -: zipWith (+) :- [4,5,6] > | > | > | For completeness, here's the `dual': > | > | > infixr 5 -! > | > (-!) = flip ($) > | > infixr 5 !- > | > (!-) = ($) > | > > | > add2 x y = x + y > | > add3 x y z = x + y + z > | > add4 x y z u = x + y + z + u > | > > | > testa1 = 1 -! add2 !- 3 + 4 > | > testa2 = 1 -! add3 1 !- 3 + 4 > | > testa3 = 1 - 2 -! add4 1 5 !- 3 * 4 > | > | All code is Haskell98. > | _______________________________________________ : : _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://haskell.org/mailman/listinfo/haskell-prime