On Sat, Oct 17, 2009 at 06:29:39PM +0000, Will Ness wrote:
Brent Yorgey
writes: By the way, the reason
map (+1) [1,2,3,4]
works but
map (-1) [1,2,3,4]
doesn't is because of an ugly corner of Haskell syntax: -1 here is parsed as negative one, rather than an operator section with subtraction. The 'subtract' function is provided exactly for this purpose, so that you can write
map (subtract 1) [1,2,3,4]
Then why wouldn't (`-`1) parse at at all? And not even (`(-)`1) ?
I know this doesn't parse, my question is, why wouldn't it be made valid syntax? It seems consistent. (`mod`2) parses, why not (`-`2) ?
`backticks` are only for making (prefix) functions into (infix) operators. - is already an infix operator, so putting it in backticks would be redundant. As for `(-)`, arbitrary expressions cannot go inside backticks, and for good reason: what would `(2 `mod`)` parse as? However, certainly different choices might have been possible. -Brent