Simon Marlow schrieb: > On 06/07/2010 13:17, Christian Maeder wrote: >> >> http://www.haskell.org/~simonmar/haskell-2010-draft-report-2/haskellch3.html >> >> >> infixexp → lexp qop infixexp (infix operator application) >> | - infixexp (prefix negation) >> | lexp >> >> This grammar rule describes a right associative nesting of (any) infix >> operators "qop" and prefix negation as binding weaker than any infix. >> >> Thus a parser would create from "- 1 /= 1&& a" the tree >> "- (1 /= (1&& a))". > > The grammar is non-ambiguous and all you have to do is flatten the > result to apply fixity resolution. I don't really see how generalising > the grammar would help - the tree still has to be flattened to apply > fixity resolution, and the parser would have to make an arbitrary choice > from one of the possible parses. Or perhaps I'm missing something here?
An ambiguous grammar (as abstract syntax for expressions) would cover the tree after fixity resolution, too. The non-ambiguous grammar only describes a temporarily wrong tree for fixity resolution. Christian _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
