What should
count (\x -> x) (replicate 10 (\y -> if 1==1 then y else undefined))
return?
2009/4/18 michael rice
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
=============
[michael@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
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