Re: Extending Functions from Manual Example

[Jason Melbye]

> On Thu, Sep 11, 2008 at 6:44 AM, Hans Aberg <address@hidden> wrote:
>
>> On 11 Sep 2008, at 05:17, Jason Melbye wrote:
>>
>>  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 {$$ = $1 + $2; }
>>>         ... other basic math ...
>>>         | FNCT '(' expr_list ')' { what goes here? }
>>>
>>> and expr_list is as you suggest above.
>>>
>>
>> It depends on what you return from the lexer (typically generated using
>> Flex). If the lexer says
>>  return '(';
>> use that in the grammar. If it says
>>  return LP;
>> use LP or (if defined using %token as above) "(".
>>
>
> Sorry if I was unclear.  I understand the difference between using '(' or
> "(", I was trying to ask if the symbol between the parenthesis should have
> been expr_list rather than expr.
>
>
>>
>>
>>  I'm not sure how to actually call the function, because I'm passing it a
>>> variable amount of parameters - as many as make up expr_list.
>>>
>>
>> You need to create a data type that can hold the expr list. Then write
>> code to compute the function application. Such data structures are called
>> "closures", that is, they represent code that should be computed later. This
>> is necessary for doing loops, too.
>>
>> So the action code should look something like in pseudocode:
>> expr_list:
>>   expr {
>>     $$ = list($1);
>>   }
>>  | expr_list "," expr {
>>     $$ = append($1, $3);
>>   }
>> ;
>>
>
> I'm not sure I completely follow the bit about creating a closure and
> computing later.  But I think I see how to do this now (or at least one way
> to do this.)  Rather than have my C functions that I wish to call of the
> form fnct(arg1, arg2, ..., argn) where n is variable, I could just have them
> all of the form fnct(int argc, param_list *params), kind of like how main
> works.  I could keep some information about them like how many and what
> types of parameters they take and do a little checking before invoking them
> to make sure I have a proper set of parameters.
>
>>
>>  Hans
>>
>>
>>
>