Sjur Gjøstein Karevoll sjurberengal at
Mon Feb 8 12:54:25 EST 2010

Måndag 8. februar 2010 17.59.59 skreiv Ross Paterson:
> But I agree they should all be legal, i.e. that unary minus should bind
> more tightly than any infix operator (as in C).

I second this, at least in general.

However, one issue is function application. Should unary minus bind tighter 
than it or not and are there special cases (spaces)? Consider:

1) foo-1
2) foo -1
3) foo - 1

If unary minus binds tighter than application then we get `foo (-1)` in all 
cases. The other way around we get `(foo) - (1)` in all cases. To me the most 
natural parsing would be

1) (foo) - (1)
2) foo (-1)
3) (foo) - (1)

Then there's also the issue of literals:

4) 1-1
5) 1 -1
6) 1 - 1

To me, all of these should parse as `(1) - (1)`. I'm a fan of treating 
literals and variables the same though (referential transparancy even in 
parsing), and that makes this problematic.

Personally I'd like to just get rid of unary minus altogether and use some 
other symbol, like _, to represent negation, but doing that would probably 
break most programs out there.

Sjur Gjøstein Karevoll

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