On Jul 31, 2007, at 6:00 , apfelmus wrote:
Chris Eidhof wrote:
When binding the function composition to a variable, the type
suddenly changes.
Prelude Control.Arrow List> :t map (length &&& head) . group
map (length &&& head) . group :: (Eq a) => [a] -> [(Int, a)]
Prelude Control.Arrow List> let encode = map (length &&& head) .
group
Prelude Control.Arrow List> :t encode
encode :: [Integer] -> [(Int, Integer)]
In short, you have to supply a type signature
encode :: (Eq a) => [a] -> [(Int, a)]
encode = map (length &&& head) . group
Note that you can do this at the GHCi prompt like this:
> let encode :: (Eq a) => [a] -> [(Int,a)]; encode = map (length &&&
head) . group
since you can't use multi-line declarations from the prompt.
--
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 university KF8NH
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