Re: Parser issues and and [[ $var ]]

[Bart Schaefer <schaefer@brasslantern.com>]

I've found a couple of other bugs with 32604, so it's probably just as
well that I didn't commit/push it.  Does anyone know why the lexer
sometimes sets (tok = DOUTBRACK, tokstr = "\220\220") and other times
(tok = DOUTBRACK, tokstr = NULL) ?

It would seem as though it ought to be consistent.  It does seem to
consistently "return" (tok = DAMPER, tokstr = NULL) for example.

On May 10,  2:09pm, Bart Schaefer wrote:
}
}     [ -t ] >/dev/null
} 
} is true in bash3.2 but false in ksh93 (including builtin test).  As far
} as I can tell, this is the only operator that behaves this way, both
} bash and ksh treat all other binary operators as strings when they
} have no argument.

Of course I meant to write "prefix operators" not "binary".

} I think the following produces syntax errors in all the places it should
} and works in the rest of the cases, but I have not yet tested it with
} new conditionals added by modules -- e.g., the recomputation of dble
} for s2 (last hunk) may need knowledge of added conditions.

With the patch from 32604 in place, I added a simple prefix operator to
the example module:

    CONDDEF("m", 0, cond_p_m, 0, -1, 0),

This should accept any number of arguments including none.  I created
cond_p_m() to return 0 if there are no arguments and 1 if there are
any arguments (recall that the C function return values are inverted
from the shell true/false return status).

After recompiling and loading zsh/example, [[ -m ]] returns true.  GDB
confirms that cond_p_m() is never being called.  The condition callback
is correctly invoked for [[ -m 1 2 ]] etc.

On the other hand, WITHOUT 32604, [[ -m ]] is a parse error, so it would
appear that prefix operators are not allowed to have no arguments.  This
should probably be documented.

Back on the first hand, in ksh93 [[ -z ]] is a parse error (that is, a
prefix operator is never tested as a plain string except in "test")
whereas [[ -m ]] is not (because there is no -m operator).  So it would
seem that once an operator is defined, it should not be allowed to
parse as a string.

Thus it would seem that the parser does need a way to explicitly test
for module-defined operators to also support non-operator non-empty
strings evaluating as true.  Or, we can decree that any string that
starts with a "-" is treated as an operator, since all module-defined
operators must start with "-", which would differ from ksh93 but not
from previous zsh.  (foo=-m; [[ $foo ]]) would still test as a string.