Am Sonntag 18 Oktober 2009 13:11:07 schrieb Will Ness:
Brent Yorgey
writes: On Sat, Oct 17, 2009 at 06:29:39PM +0000, Will Ness wrote:
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
backticks could've been made no-op for operators. What's so wrong with (`:`[])? It'd just be the same as (:[]).
Makes writing the parser more complicated. Makes reading code more irritating.
Except for `-`, where it would finally provide us with possibility to write a shortcut for the ugly (flip (-) 1) as (`-`1).
That's ugly too. My favourite is subtract 1.
(2`mod`) is a unary operation :: (Integral a) => a -> a. Putting it inside backticks would require it be a binary infix op, causing a type mis-match.
instance (Integral a) => Integral (b -> a) where ... Evil, yes, but then f `(2 `mod`)` x would type-check. But anyway, there are operators where a backticked section would type-check: f `(g `.`)` x That's not good.
For (-) it could choose the binary version over the unary.
Or it could stay illegal for the parenthesised expressions, and just made legal syntax for operators, as (`:`[]).
I don't know how easy or even possible it is to implement; I'm just saying it makes sense, for me.
But it has downsides.