Simon Marlow schrieb: [...] >> 1. "- 1 * 1" is accepted as legal pattern, but differently resolved for >> expressions! Should one not reject these (rare) patterns, too? > > That's the GHC bug, right?
Yes! >> 2. I would rather allow "1 * - 1" and "1 + - 1" to be legal as >> expressions (with its unambiguous interpretation). > > Yes, me too, but that's a matter for a new proposal. > >> 3. Associativity should not matter for the non-binary "-"! >> >> So the following resolutions are possible: >> >> "1 + - 2 + 3" ~~~> "(1 + -2) + 3" >> "1 + - 2 * 3" ~~~> "1 + -(2 * 3)" >> >> infix 6 ## -- same precedence like "+" but different associativity >> >> "- 1 ## 2" ~~~> "(-1) ## 2" > > Yes, again I agree. The current fixity resolution is more strict than > it needs to be. The intention in Haskell 2010 was not to change the way > fixity resolution worked, but rather to avoid the problems caused by > having it as part of the grammar. The grammar (in particular an ambiguous one) describes a superset of the language and need not change with a changed fixity resolution (or type analysis). > > If you make a proposal to change this, then I would probably support it. A larger case would be "1 * - 2 * 3", that I would resolve to "1 * - (2 * 3)" by resolving everything after "-" first. This is sort of an arbitrary choice, but probably ok and in the same spirit than resolving "- 2 * 3" to "- (2 * 3)". C. _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
