[Haskell-cafe] Re: How to "Show" an Operation?
Brandon S. Allbery KF8NH
allbery at ece.cmu.edu
Fri Jun 11 00:43:44 EDT 2010
On Jun 10, 2010, at 17:38 , Martin Drautzburg wrote:
>> instance Applicative Named where
>> pure x = Named "" x
>> (Named s f) <*> (Named t v) = Named (s ++ "(" ++ t ++ ")") (f v)
> Applicative. Need to study that
The above is just the Functor, rephrased in Applicative style. <*> is
exactly fmap. Likewise, Monad has a function "liftM" which is exactly
fmap. (For historical reasons, these are not related the way they
should be: all Monads should be Applicatives, all Applicatives should
be Functors, and all Functors should be instances of an even more
primitive class Pointed.)
> According to Hoogle permutations should be in Data.List. Mine (GHCI
> does not seem to have it. Seems to have something to do with "base",
> that is.
Things have gradually been moving out of base; you probably need to
install "containers" from Hackage.
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university KF8NH
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