Re: Extending Functions from Manual Example

[Jason Melbye]

On Wed, Sep 10, 2008 at 3:59 AM, Hans Aberg <address@hidden> wrote:

> On 10 Sep 2008, at 05:39, Jason Melbye wrote:
>
>> I have been reading through the Bison manual the past couple days.  I
>> really
>> liked the three examples, especially the last - the multifunction
>> calculator.  Since reading that I have been wondering if there was a
>> general
>> way to describe a function that can take on any number of arguments in the
>> grammer rules?
>>
>> I suppose that I could just do something like,
>>
>> | FNCT '(' exp ')'   { $$ = (*($1->value.fnctptr))($3); }
>> | FNCT '(' exp ',' exp ')'   { $$ = (*($1->value.fnctptr))($3,$5); }
>> | FNCT '(' exp ',' exp ',' exp ')'   ...
>>
>>
>> I could go on like that to all for as many arguments as I wanted to /
>> needed
>> to.  However, I would also like to create a "plug-in" system where users
>> can
>> create their own functions and add them to the application.  Thus a
>> avoiding
>> a limit on arguments would be desirable.
>>
>
> You need to create recursive rules. If lists are non-empty, write:
>
> expr_list:
>    expr {
>      ...
>    }
>  | expr_list "," expr {
>      ...
>    }
> ;
>
> If empty lists are admitted, simply delete the first "expr" in the above.
>
> Then use it:
>  FNCT '(' expr ')'
>
> Some prefer not using the '...' construct. So one can write:
>
> %token LP "("
> %token RP ")"
>
>  FNCT "(" expr ")"
>

Should those FNCT '(' expr ')' / FNCT "(" expr ")" lines say FNCT '('
expr_list ')' (or "(", ")" ) instead?  I'm still struggling to construct the
action that calls the function as well, passing all the arguments.  So say I
had this:

expr:    NUM
         | expr '+' expr {$$ = $1 + $2; }
         ... other basic math ...
         | FNCT '(' expr_list ')' { what goes here? }

and expr_list is as you suggest above.

I'm not sure how to actually call the function, because I'm passing it a
variable amount of parameters - as many as make up expr_list.

I appreciate the help,
Jason