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99 questions/Solutions/4

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Line 8: Line 8:
   
 
<haskell>
 
<haskell>
myLength' = foldl (\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
+
myLength''' = foldr (\_ -> (+1)) 0
 
myLength'''' = foldr ((+) . (const 1)) 0
 
myLength'''' = foldr ((+) . (const 1)) 0
 
</haskell>
 
</haskell>

Revision as of 23:08, 12 January 2011

(*) 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
myLength'''' =  foldr ((+) . (const 1)) 0
myLength' xs = snd $ last $ zip xs [1..] -- Just for fun
This is
length
in
Prelude
.