Re: [Haskell-cafe] Is there a way to find out the type inferred for a local function inside another function? :)

7 Apr 2011

      On Thursday 07 April 2011 21:52:29, KC wrote:
...
There are probably better ways, but:

module Infer where

foo :: Num a => [a] -> a
foo = go 0 0
  where
    go :: b
    go i s (x:xs) = go (i+1) (s+i*x) xs
    go _ s _ = s

$ ghc Infer
[1 of 1] Compiling Infer            ( Infer.hs, Infer.o )

Infer.hs:7:5:
    Could not deduce (b ~ (a0 -> a0 -> [a0] -> a0))
    from the context (Num a)
      bound by the type signature for foo :: Num a => [a] -> a
      at Infer.hs:(4,1)-(8,16)
      `b' is a rigid type variable bound by
          the type signature for go :: b at Infer.hs:7:5
    The equation(s) for `go' have three arguments,
    but its type `b' has none
    In an equation for `foo':
        foo
          = go 0 0
          where
              go :: b
              go i s (x : xs) = go (i + 1) (s + i * x) xs
              go _ s _ = s

sort of does it.

Re: [Haskell-cafe] Is there a way to find out the type inferred for a local function inside another function? :)

Daniel Fischer