On Thu, 26 Sep 2002, Sean O'Rourke wrote:
: Thanks for taking the time to write this out.
:
: On Thu, 26 Sep 2002, John Williams wrote:
: > perl6 operator precedence
: >
: > left terms and list operators (leftward) [] {} () quotes
: > left . and unary .
: > nonassoc ++ --
: > left is but
:
: This would lead to some scary things, I think:
:
: $a = 3 + 4 but false
: => (= $a (+ 3 (but 4 false)))
:
: Of course, so does having low precedence:
:
: $a = 3 but false + 4
: => (= $a (but 3 (+ false 4)))
:
: but I think the latter is unnatural enough that it deserves parens, so I'd
: put 'but' above comma (and probably '='), but below just about everything
: else.
Could perhaps unify with C<..>. Wouldn't hurt for it to be non-associative like C<..>.
: > Larry mentions that other precedence unifications are possible. I can see
: > the following as possibilites. Are there others?
: > & with &&
: > | with ||
:
: It seems like a good idea to me to encourage people to think of bitwise
: ops as mathematical, not logical, so I'd rather see them with different
: precedences. Plus, anything that significantly goes against people's
: hard-wired C expectations will just lead to confusion and pain. Finally,
: having '|' below '&&' will probably lead to strange things, e.g.
:
: 1|2 && 3|4
: => 1 | (2 && 3) | 4
I'd be more inclined to unify & and | with * and +, since that's
exactly what they are in Boolean algebra, where 1*1 == 1. I think
the argument that it breaks C compatibily is weak in this case,
since almost everyone admits that C is broken in this respect.
Alternately, we take | and & away from bitwise ops and do something
more useful with them. I have been asked privately by a sight
impaired person to consider using | as the separator for parallel
streams rather than the almost invisible ; character, for instance.
Being a bit sight impaired myself at the moment, I have great empathy...
Larry
