[Haskell-cafe] Re: Top Level etc.

[Keean Schupke]

Ben Rudiak-Gould wrote:

>    > len :: [a] -> Int
>    >
>    > len xs = let ?accum = 0 in len' xs
>    >
>    > len' :: forall a. (?accum :: Int) => [a] -> Int
>    >
>    > len' [] = ?accum
>    > len' (x:xs) = let ?accum = ?accum + (1::Int) in len' xs
>
>    *Main> :t len'
>    len' :: forall a. (?accum :: Int) => [a] -> Int
>    *Main> len "hello"
>    5

I don't get this. The second answer (the one quoted above) must be wrong...
len' gets a value only in the empty '[]' case. The recursion is such 
that the value
of '?accum' is incremented on the return of the recursively called 
function, therefore
the value of '?accum' in the case '[]' is always zero! How on earth does 
this get
the answer five?

    Keean,