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m (NTUA solution ;-))
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</haskell>
 
</haskell>
   
  +
This is <hask>length</hask> in <hask>Prelude</hask>.
  +
  +
A fancier one! :-)
 
<haskell>
 
<haskell>
 
myLength = foldl (const . (+1)) 0
 
myLength = foldl (const . (+1)) 0
 
</haskell>
 
</haskell>
 
This is <hask>length</hask> in <hask>Prelude</hask>.
 

Revision as of 13:29, 18 July 2012

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

myLength           :: [a] -> Int
myLength []        =  0
myLength (_:xs)    =  1 + myLength xs
 
myLength' :: [a] -> Int
myLength' list = myLength_acc list 0 -- same, with accumulator
	where
		myLength_acc [] n = n
		myLength_acc (_:xs) n = myLength_acc xs (n + 1)
myLength'     =  foldl (\n _ -> n + 1) 0
myLength''    =  foldr (\_ n -> n + 1) 0
myLength'''   =  foldr (\_ -> (+1)) 0
myLength''''  =  foldr ((+) . (const 1)) 0
myLength''''' =  foldr (const (+1)) 0
myLength' xs = snd $ last $ zip xs [1..] -- Just for fun
myLength''   = snd . last . (flip zip [1..]) -- Because point-free is also fun
myLength'''  = fst . last . zip [1..] -- same, but easier
myLength = sum . map (\x -> 1)
This is
length
in
Prelude
.

A fancier one! :-)

myLength = foldl (const . (+1)) 0