Infix expressions: Difference between revisions

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<pre>
==Disclaimer==
WORK IN PROGRESS
This is a '''WORK IN PROGRESS''', transcribed from an email log on haskell-prime@haskell.org.


From: dons@cse.unsw.edu.au (Donald Bruce Stewart)
==Mail info==
To: Simon Peyton-Jones <simonpj@microsoft.com>
The original header posted here:
Date: Wed, 15 Mar 2006 23:25:34 +1100
From: dons@cse.unsw.edu.au (Donald Bruce Stewart)
Cc: haskell-prime@haskell.org, oleg@pobox.com
To: Simon Peyton-Jones <simonpj@microsoft.com>
Subject: Re: Infix expressions
Date: Wed, 15 Mar 2006 23:25:34 +1100
Cc: haskell-prime@haskell.org, oleg@pobox.com
Subject: Re: Infix expressions


simonpj:
This refered to a variety of articles, the original was said to be:
> I often wish that cool tricks like this could be collected on the
[http://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html haskell-cafe message]
> Haskell web site. Now that it's a wiki, anyone could do that.
 
==The solution==
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.
<haskell>
  xs `zipWith (+)` ys
</haskell>
   
   
Yes, this is _exactly_ the kind of thing to add to the Idioms
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.
page of the wiki, here:
 
  http://www.haskell.org/haskellwiki/Category:Idioms
For ease of reference, here's their elegant solution:
<haskell>  
So if anyone knows of an interesting Haskell trick, and wants to write
infixr 0 -:, :-
about it,  add a page!
data Infix f y = f :- y
x -:f:- y = x `f` y
We should take advantage of the fact we have a lot of good authors in
main = print $ [1,2,3] -: zipWith (+) :- [4,5,6]
the community to document all the interesting things that we come up
</haskell>
with
 
For completeness, here's the `dual':
-- Don
<haskell>
infixr 5 -!
> 
(-!) = flip ($)
> Simon
infixr 5 !-
> 
(!-) = ($)
> | -----Original Message-----
 
> | From: haskell-prime-bounces@haskell.org
add2 x y = x + y
> [mailto:haskell-prime-bounces@haskell.org] On Behalf Of
add3 x y z = x + y + z
> | oleg@pobox.com
add4 x y z u = x + y + z + u
> | 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
> |
</haskell>
> | 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.
> | _______________________________________________
:
:
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Haskell-prime mailing list
Haskell-prime@haskell.org
http://haskell.org/mailman/listinfo/haskell-prime


</pre>
----


[[Category:Idioms]]
[[Category:Idioms]]

Revision as of 03:01, 21 March 2006

Disclaimer

This is a WORK IN PROGRESS, transcribed from an email log on haskell-prime@haskell.org.

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': 

 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
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