99 questions/Solutions/4

(Difference between revisions)

Revision as of 01:39, 20 November 2010

(*) Find the number of elements of a list.

myLength           :: [a] -> Int
myLength []        =  0
myLength (_:xs)    =  1 + myLength xs

myLength'   =  foldl (\n _ -> n + 1) 0
myLength''  =  foldr (\_ n -> n + 1) 0
myLength''' =  foldr (\_ -> (+1)) 0

This is

length

Prelude

@@ Line 8: / Line 8: @@
 <haskell>
-myLength'  =  foldr (\_ n -> n + 1) 0
+myLength'   =  foldl (\n _ -> n + 1) 0
-myLength'' =  foldr (\n _ -> n + 1) 0
+myLength''  =  foldr (\_ n -> n + 1) 0
+myLength''' =  foldr (\_ -> (+1)) 0
 </haskell>
 This is <hask>length</hask> in <hask>Prelude</hask>.