Difference between revisions of "Infix expressions"

Revision as of 09:44, 19 December 2007

Mail info

The original header posted here:

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

This refered to a variety of articles, the original was said to be: haskell-cafe message

The solution

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 in the article referenced above.

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':

infixl 5 -!
(-!) = flip ($)
infixl 5 !-
(!-) = ($)

add2 x y = x + y
add3 x y z = x + y + z
add4 x y z u = x + y + z + u
sub3 x y z = x + y - z

testa1 = 1 -! add2 !- 3 + 4
testa2 = 1 -! add3 1 !- 3 + 4
testa3 = 1 - 2 -! add4 1  5 !- 3 * 4
-- 17 = (1-2) + (1+5) + (3*4) 
testa4 = 1 - 2 -! sub3 1  !- 3 * 4 
-- -12 = (1-2) + (1) - 12

@@ Line 1: / Line 1: @@
+==Mail info==
-<pre>
+The original header posted here:
-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
+This refered to a variety of articles, the original was said to be:
-Display all headersFrom: dons@cse.unsw.edu.au (Donald Bruce Stewart)
+[http://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html haskell-cafe message]
-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
+==The solution==
-simonpj:
+In Haskell we write <hask>`f`</hask> 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.
-> I often wish that cool tricks like this could be collected on the
+<haskell>
-> Haskell web site.  Now that it's a wiki, anyone could do that.
+   xs `zipWith (+)` ys
+</haskell>
+Chung-chieh Shan and Dylan Thurston showed the Haskell98 solution for exactly the same example, in their article `Infix expressions', back in 2002 in the article referenced above.
-Yes, this is _exactly_ the kind of thing to add to the Idioms
-page of the wiki, here:
+For ease of reference, here's their elegant solution:
-   http://www.haskell.org/haskellwiki/Category:Idioms
+<haskell>
+ infixr 0 -:, :-
-So if anyone knows of an interesting Haskell trick, and wants to write
+ data Infix f y = f :- y
-about it,  add a page!
+ x -:f:- y = x `f` y
+ main = print $ [1,2,3] -: zipWith (+) :- [4,5,6]
-We should take advantage of the fact we have a lot of good authors in
+</haskell>
-the community to document all the interesting things that we come up
-with
+For completeness, here's the `dual':
+<haskell>
--- Don
+infixl 5 -!
+(-!) = flip ($)
->
+infixl 5 !-
-> Simon
+(!-) = ($)
->
-> | -----Original Message-----
+add2 x y = x + y
-> | From: haskell-prime-bounces@haskell.org
+add3 x y z = x + y + z
-> [mailto:haskell-prime-bounces@haskell.org] On Behalf Of
+add4 x y z u = x + y + z + u
-> | oleg@pobox.com
+sub3 x y z = x + y - z
-> | Sent: 15 March 2006 04:34
-> | To: doaitse@cs.uu.nl; haskell-prime@haskell.org
+testa1 = 1 -! add2 !- 3 + 4
-> | Subject: Infix expressions
+testa2 = 1 -! add3 1 !- 3 + 4
-> |
+testa3 = 1 - 2 -! add4 1  5 !- 3 * 4
-> |
+-- 17 = (1-2) + (1+5) + (3*4)
-> | Doaitse Swierstra wrote:
+testa4 = 1 - 2 -! sub3 1  !- 3 * 4
-> | > In Haskell we write `f` in order to infixify the identifier f. In
+-- -12 = (1-2) + (1) - 12
-> ABC
+</haskell>
-> | > 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
-> _______________________________________________
-> Haskell-prime mailing list
-> Haskell-prime@haskell.org
-> http://haskell.org/mailman/listinfo/haskell-prime
-_______________________________________________
-Haskell-prime mailing list
-Haskell-prime@haskell.org
-http://haskell.org/mailman/listinfo/haskell-prime
-</pre>
-----
 [[Category:Idioms]]
+[[Category:Syntax]]

Difference between revisions of "Infix expressions"

Revision as of 09:44, 19 December 2007

Mail info

The solution

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