Though I haven't tried it out, it's trying to use my function to count functions.
The first argument is the identity function. The second argument is a list of a different form of the identity function. Though the two identity functions, given the same input, would produce the same output, I doubt they would be equal. So my guess at an answer would be zero. Michael --- On Sat, 4/18/09, Eugene Kirpichov <ekirpic...@gmail.com> wrote: From: Eugene Kirpichov <ekirpic...@gmail.com> Subject: Re: [Haskell-cafe] General function to count list elements? To: "michael rice" <nowg...@yahoo.com> Cc: haskell-cafe@haskell.org Date: Saturday, April 18, 2009, 11:03 AM What should count (\x -> x) (replicate 10 (\y -> if 1==1 then y else undefined)) return? 2009/4/18 michael rice <nowg...@yahoo.com>: > Is there a general function to count list elements. I'm trying this > > count :: a -> [a] -> Int > count x ys = length (filter (== x) ys) > > with this error upon loading > > ============= > > [mich...@localhost ~]$ ghci count > GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer ... linking ... done. > Loading package base ... linking ... done. > [1 of 1] Compiling Main ( count.hs, interpreted ) > > count.hs:2:29: > Could not deduce (Eq a) from the context () > arising from a use of `==' at count.hs:2:29-32 > Possible fix: > add (Eq a) to the context of the type signature for `count' > In the first argument of `filter', namely `(== x)' > In the first argument of `length', namely `(filter (== x) ys)' > In the expression: length (filter (== x) ys) > Failed, modules loaded: none. > Prelude> > > ============= > > Not sure what it's trying to tell me other than I need an (Eq a) somewhere. > > Michael > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Eugene Kirpichov Web IR developer, market.yandex.ru
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