If naturals have a perfectly reasonable subtraction then they also have a
perfectly reasonable negate; the default is 0-x.
(Oh, subtraction wasn't THAT reasonable, you say. :) )
-- Lennart
On 10/17/07, John Meacham
On Tue, Oct 16, 2007 at 06:27:19PM -0300, Isaac Dupree wrote:
Peter Verswyvelen wrote:
Personally I could also live with allowing no space between the minus sign and the number... If you leave a space, - becomes the subtract operator.
I once thought that... there was the opposition that (x-1) subtraction of a constant appears too often. And I found that I myself wrote that several times. And saying "whitespace on the left but not the right" seems too complicated for Haskell lexer semantics. So the current situation is just unhappy, that's all. (and maybe compiler warnings could still be implemented)
not just unhappy, but inefficient. -10 tranlates to (negate (fromInteger 10)) requiring 2 indirect class calls rather than what one might expect (fromInteger -10)
also, negate in Num is sort of ugly IMHO. It would be nice if it wern't there. Things like naturals have a perfectly reasonable subtract, but no negate.
I think losing x-1 would be worth it. but I know there were some other ideas out there that might be preferable but could still be handled at the lexing stage rather than the parsing one...
John
-- John Meacham - ⑆repetae.net⑆john⑈ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe