Kind error in GHC-7.4.1, works in GHC-7.2.2

9 Feb 2012

      Hello,

I have some code that compiled fine in GHC-7.2.2 but fails in
GHC-7.4.1 with a kind error.

{-# LANGUAGE MagicHash, NoImplicitPrelude, PackageImports #-}
import "base" Data.Function ( ($) )
import "base" GHC.Exts ( Int(I#) )
import "base" Prelude ( Integral, fromIntegral, toInteger )
import "integer-gmp" GHC.Integer.Logarithms ( integerLogBase# )

intLog :: (Integral a) => a -> a
intLog x = fromIntegral $ I# $ integerLogBase# 10 (toInteger x)

This results in the following error:

    Couldn't match kind `#' against `*'
    In the second argument of `($)', namely
      `I# $ integerLogBase# 10 (toInteger x)'
    In the expression:
      fromIntegral $ I# $ integerLogBase# 10 (toInteger x)
    In an equation for `intLog':
        intLog x = fromIntegral $ I# $ integerLogBase# 10 (toInteger x)

Simply eliminating some $'s using parenthesis solves the problem:

intLog x = fromIntegral $ I# (integerLogBase# 10 (toInteger x))

Why do I get the above kind error? Could it be a bug in GHC?

Kind error in GHC-7.4.1, works in GHC-7.2.2

Roel van Dijk