On 03/02/2006, at 9:25 AM, Wolfgang Jeltsch wrote:
Am Mittwoch, 1. Februar 2006 01:32 schrieb Patryk Zadarnowski:
[...]
The proposal would be to remove the unary "-" altogether, and,
instead,
extend the lexical syntax of numeric constant to allow "+" and "-"
prefix.
Would this mean that (-x) is a section while (-1) isn't? That
would be
confusing.
Apart from this, I would like to see the only unary operator of
Haskell
removed.
Yes, it *would* mean that (-x) and (- 1) are sections while (-1)
isn't, and
yes, that would be slightly confusing (and a good compiler might want to
issue a warning whenever it sees a construct of the form (-identifier).
However, it is NOT more confusing than what we already have with
the (.) operator. Consider:
(Just . not) is a perfectly reasonable function of type (Bool ->
Maybe Bool)
But:
(Just.not) has a completely different meaning (and is probably
illegal unless
you have a module called "Just", which exports a function called
(not).)
In the case of the (.) operator, the confusion is more significant,
since the meaning
is context-sensitive. With the proposed "-" operator, it would be
purely lexical, and
therefore easy to warn about (if the compiler wishes to do so.)
In both cases, accidentally omitting a space will result in a
compiler or type error
anyway, since (-x) has a different type than (- x), so such accidents
will be picked
by the compiler rather than generating invalid code.
In summary: yes, the change would create *some* confusion. But much
less confusion
than that caused by the current treatment of (-).
Pat.
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