On 01/08/2011 11:59 AM, Joel E. Denny wrote:
> On Sat, 8 Jan 2011, Paul Eggert wrote:
>
>> On 01/08/2011 10:29 AM, Joel E. Denny wrote:
>>> id -|({letter}|-({letter}|-))({letter}|[-0-9])*
>>
>> Sorry, I guess I don't understand the point of this.
>> Why should "---39---" be an identifier?
>
> I thought we were adding the simple rule that an identifier cannot begin
> with a negative integer. "---39---" does not begin with a negative
> integer.
That depends on how it is parsed. If we are mentally parsing
it using the rules of C, "---39---" starts with a "--" token,
and then we have the same problem as before.
>> And if so,
>> why should "--39--" *not* be an identifier?
>
> Who says it shouldn't?
The rule you proposed above says it shouldn't.
>> Can someone remind me why we're doing this?
>
> It's consistent with other identifiers in Bison.
Sorry, now I'm lost. The rule for "id" *is* the rule for
identifiers in Bison, surely.
What I'm asking is, why did we change the rule to allow "-"
in identifiers, and to embed these identifiers into C and
Java code, when this causes obvious problems?
The issue that started this thread is one example of
such a problem: the problem of the above suggestion (which
apparently is buggy) is another.
Perhaps we can take a step back here. Why is it important
that we allow the syntax $B in C code, where B is a Bison
identifier? If Bison identifiers are not the same as C
identifiers, the resulting code will be hard to explain
and to read. Wouldn't it be better to require an escape
syntax for these identifiers? Something like ${B}, or $"B",
or $[B], or $(B), or etc.? That will make it more obvious
to the reader where the Bison identifier stops and the C code
starts up again.
For example, when suppose we have the following code
in a Bison + C parser:
$x--;
Most programmers would expect this to subtract one from $x,
not to compute the value of the identifier "x--" and then
discard it. If a programmer really wants to name their
identifier "x--" they should write "${x--}" or something
like that.
