Reply to Miles,
BCS wrote:
I think not.
x ? y : a ? b : c => (x ? y : a) ? b : c
or
x ? y : a ? b : c => x ? y : (a ? b : c)
without checking the actual syntax you can't tell which of the above
will be used and (according to bearophile) if ?: followed after
+/-/etc the first would be.
It simply can't be the first, due to the kind of parser used for C and
most of its derived languages (D included). When a '?' is found, the
parser recurses until it finds a ':' (it gets stuck in a branch of the
syntax tree until a colon token is found).
This is in how the language is defined
(http://www.digitalmars.com/d/2.0/expression.html):
ConditionalExpression:
OrOrExpression
OrOrExpression ? Expression : ConditionalExpression
So, the third operand to the ternary operator is a
ConditionalExpression itself, the parser have no reason to finish this
evaluation branch if it finds another '?', it naturally recurses.
So, x ? y : a ? b : c => x ? y : (a ? b : c).
You have just proven my exact point. To find how it parses you need to dig
up the syntax, as you just did (Note I said that you can't tell how it's
parsed *without* doing that).
Also note that most (or all) of the other operators in C/C++/C#/D/etc go
the other way:
OrOrExpression:
AndAndExpression
OrOrExpression || AndAndExpression
But I think that I know what kind of ambiguity you are talking about
now... For me, ambiguity is something like the <...> C++ template
definition/instantiation operator, or the function declaration/object
variable definition ambiguity.
Yes, I think you've spotted the point. I'm referring to ambiguities that
will cause problems with <joke>I-BAL</joke> type parsers.
