S. Doaitse Swierstra schrieb:
weird :: Int -> Int weird = (if True then 3 else 5+)
is perfectly correct Haskell?
Yes, this is legal according to the grammar http://haskell.org/onlinereport/syntax-iso.html but rejected by ghc and hugs, because "5+" is illegal. The problem is to allow let-, if-, do-, and lambda-expressions to the left of operators (qop), because for those the meta rule "extend as far as possible" should apply. Switching to the new grammar http://hackage.haskell.org/trac/haskell-prime/wiki/FixityResolution infixexp -> exp10 qop infixexp | - infixexp | exp10 should be replaced by: infixexp -> fexp qop infixexp | exp10 (omitting the negate rule) or shorter: "infixexp -> { fexp qop } exp10" Left sections should look like: ( {fexp qop} fexp qop ) It would be even possible to avoid parenthesis around sections, because a leading or trailing operator (or just a single operator) uniquely determines the kind of expression. Negation should be added independently to fexp (and possibly to exp10, too) fexp -> [fexp] aexp (function application) minusexp -> fexp | - fexp infixexp -> minusexp qop infixexp | exp10 | - exp10 (unless some wants the old FORTRAN behaviour of unary "-" to bind weaker than infix multiplication and exponentiation.) Cheers Christian