Re: exist, configure, doc2tex and \index

[Daniel J S. <dan...@ie...>]

Petr Mikulik wrote:
>> You are missing my point.
>> foo is a variable.  It may hold a string ("xxx") or it may hold an 
>> integer (9).
>> It is legal to call
>>     if (exists(foo))
>> in the first case, and the return code is 1, which tells you that foo 
>> contains
>> the name of a defined variable.
>>
>> As I see it, if foo = 9 then  exists(foo) should return 0, which tells 
>> you that
>> foo does _not_ contain the name of a defined variable.  That is what 
>> it does
>> now, and I think it is correct.  Daniel's patch would have it error 
>> out rather
>> than returning.
> 
> 
> Ok, you are right.
> 
>>> gnuplot> help exists
>>>   `exists("X")` returns 1 if a variable named X has been defined,
>>>   otherwise it returns 0.
>>
>>    ^^^^^^^^^^^^^^^^^^^^^^^
>>
>> That is exactly what I am saying.  If the argument to exists() is not a
>> defined variable name  (i.e. a string), then exists() should return 0.
>> Not error out;  return 0.
> 
> 
> Could you perhaps add this into "help exists"?

More than that.  Rephrase things to remove ambiguity.  One can look at the above help and assume implicitly that X must be inside a string.  How about:

`exists(ARG)` returns 1 if its argument is a string containing
a variable that has been defined, e.g., ARG="X" where X has
been defined.  Otherwise the function returns 0.

THEN we must change this behavior

gnuplot> print exists()
                      ^
         invalid expression
gnuplot> print exists(empty)
         undefined variable: empty

so that both return 0.  That or change the help description to refine things even further:

`exists(ARG)` returns 1 if its argument is a string containing
a variable that has been defined, e.g., ARG="X" where X has
been defined.  Otherwise the function returns 0 if ARG is a
valid expression and errors if ARG is not a valid expression.

Daniel