Re: [Haskell-cafe] binary operator modifiers
liftM2 (/) sum length. Anyway, the closest you can get in Haskell is
something like this, using the infix expressions of Ken Shan and Dylan
Thurstonhttp://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html
Hmm.. that might be decent if you added rules to pretty-print them in
lhs2tex. The src code would be slightly messy but the formatted code would
be very clean. And it opens the doors for other binop decorators.
Interesting idea.
I finally get my lhs2tex set up and put together a better example
of what I was talking about:
http://www.thenewsh.com/%7Enewsham/Hats.pdf
Though I don't know if you can coax lhs2tex into accepting something like
%format -:liftM2 (+):- = \widehat{+}
Tim Newsham
http://www.thenewsh.com/~newsham/
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Re: [Haskell-cafe] binary operator modifiers
On 10/29/07, Tim Newsham [EMAIL PROTECTED] wrote:
I would love to have the ability to define binary operator modifiers.
For example:
f \overline{op} g = liftM2 op f g
f \overleftarrow{op} n = liftM2 op f (return n)
n \overrightarrow{op} g = liftM2 op (return n) f
\widehat{f} x = liftM f x
so that for example you could define functions like:
(*3) \overline{+} (/2)
and
3 \overrightarrow{+} \widehat{read} getContents
Obviously you could write this out the long way:
liftM2 (3+) $ liftM read getContents
or go through the trouble of defining a bunch of binops
f + g = liftM2 (+) f g
n + g = return n + g
f + n = f + return n
read' = liftM read
(*3) + (/2)
3 + read' getContents
but doing this for more than one or two operators gets tedious
quickly...
Is there any way in Haskell to modify binops in this way and still
be able to use them infix? If not, has anyone considered supporting
strange syntaxes like this?
I've wanted this at times, too, due to using a lot of J a year or so ago. J
has some weird parsing/semantics rules so that f g h essentially means
liftM2 g f h. For example, avg =. +/ % # is the J equivalent of avg =
liftM2 (/) sum length. Anyway, the closest you can get in Haskell is
something like this, using the infix expressions of Ken Shan and Dylan
Thurstonhttp://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html
:
import Control.Monad
import Control.Monad.Instances
infixr 0 -:, :-
data Infix f y = f :- y
x -: f :- y = x `f` y
ov op = liftM2 op
ovL op f n = liftM2 op f (return n)
ovR op n f = liftM2 op (return n) f
hat f = liftM f
*Main :t (*3) -:ov (+):- (/2)
(*3) -:ov (+):- (/2) :: forall a1. (Fractional a1) = a1 - a1
*Main ((*3) -:ov (+):- (/2)) 7
24.5
*Main :t 3 -:ovR (+):- ((hat read) getContents)
3 -:ovR (+):- ((hat read) getContents) :: forall a. (Num a, Read a) = IO a
It works (?), but it's pretty ugly and hardly seems worth it, unfortunately.
-Brent
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Re: [Haskell-cafe] binary operator modifiers
liftM2 (/) sum length. Anyway, the closest you can get in Haskell is something like this, using the infix expressions of Ken Shan and Dylan Thurstonhttp://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html : [] It works (?), but it's pretty ugly and hardly seems worth it, unfortunately. Hmm.. that might be decent if you added rules to pretty-print them in lhs2tex. The src code would be slightly messy but the formatted code would be very clean. And it opens the doors for other binop decorators. Interesting idea. -Brent Tim Newsham http://www.thenewsh.com/~newsham/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] binary operator modifiers
On Oct 29, 2007, at 3:36 , Tim Newsham wrote: or go through the trouble of defining a bunch of binops f + g = liftM2 (+) f g n + g = return n + g f + n = f + return n read' = liftM read This looks a lot like Control.Applicative to me. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] binary operator modifiers
Hello Tim, Monday, October 29, 2007, 10:36:18 AM, you wrote: or go through the trouble of defining a bunch of binops Is there any way in Haskell to modify binops in this way and still be able to use them infix? Template Haskell looks like an perfect tool for implementing this -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
