This program:
module Main where
f = map (++"a"++"b")
g = map ("a"++"b"++)
main = do print (f ["x","y","z"])
print (g ["x","y","z"])
gives the following error messages with ghc (versions 4.08.2 and 5.02):
plusplus.hs:3:
The operator `++' [infixr 5] of a section
must have lower precedence than the operand `++' [infixr 5]
In the section: `(++ ("a" ++ "b"))'
plusplus.hs:4:
The operator `++' [infixr 5] of a section
must have lower precedence than the operand `++' [infixr 5]
In the section: `(("a" ++ "b") ++)'
I believe this is the wrong behaviour - the first (right) section is
perfectly valid Haskell'98 because the operator is right associative.
Hugs, hbc, and nhc98 all accept it. Check also section 3.5 (p.17)
of the Report.
The second (left) section is indeed incorrect, again because the
operator is right associative.
Regards,
Malcolm
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