Required Named Params and go write your own grammar

[Abhijit A. Mahabal]

As I try writing P6 programs I do find myself needing required named
params, and I thought I'd like something like ++$named_req for myself as a
shorthand for +$named_req is required or whatever is decided.

Now, larry often says (only partly jokingly) go write your own grammar.
But I do not know how I'd change/modify/append the grammar to accomodate
that cosmetic change above. Needing to know the entire P6 grammar
isn't mouth watering. I am sure this has been discussed before, so can
somebody please point me to some place where I can start reading about
this?

macros does not seem to be an answer as I seem to think of them as
defining syntax for new commands that you are writing. (In this case, I do
not know where I would put the is parsed trait). I may be wrong and
macros in some form are the answer. Either way, I'd appreciate any
thoughts/answers/pointers on this.

--Abhijit

Abhijit A. Mahabal  http://www.cs.indiana.edu/~amahabal/

Re: Required Named Params and go write your own grammar

[Juerd]

Abhijit A. Mahabal skribis 2004-05-04 10:27 (-0500):
 As I try writing P6 programs I do find myself needing required named
 params, and I thought I'd like something like ++$named_req for myself as a
 shorthand for +$named_req is required or whatever is decided.

What's wrong with just specifying them as positional ones? Don't
document the feature and you'll effectively have required named
parameters.

Or am I missing something?

 the entire P6 grammar

Are parts already available in Perl 6 rule syntax?


Juerd

Re: Required Named Params and go write your own grammar

[Luke Palmer]

Abhijit A. Mahabal writes:
 As I try writing P6 programs I do find myself needing required named
 params, and I thought I'd like something like ++$named_req for myself as a
 shorthand for +$named_req is required or whatever is decided.
 
 Now, larry often says (only partly jokingly) go write your own grammar.
 But I do not know how I'd change/modify/append the grammar to accomodate
 that cosmetic change above. Needing to know the entire P6 grammar
 isn't mouth watering. I am sure this has been discussed before, so can
 somebody please point me to some place where I can start reading about
 this?

Well, there's no official grammar for Perl 6 anywhere.  The most
definitive source you can find is in A6.  In that document we find:

rule parameter :w {
[ type? zone? variable trait* defval?
| \[ signature \]   # treat a single array ref as an arg list
]
}

rule zone {
[ \?   # optional positional
| \*   # slurpy array or hash (or scalar)
| \+   # optional named-only
]
}

It would seem that this is the place to create your ++ zone.  Here we
go:

grammar Grammar::ReqNamed {
is Grammar::Perl;

rule zone {
  \+ before: \+ { 
.substr(.pos, 1) = '';
s/after: variable/is required/;
fail;
  }
| next
}
}

That probably doesn't work.  But it gets close.  I'd much prefer to
parse it and then change the syntax tree in the walking phase, but I
don't know how to do that yet.

Luke

Re: Required Named Params and go write your own grammar

[Abhijit A. Mahabal]

On Tue, 4 May 2004, Luke Palmer wrote:

 Abhijit A. Mahabal writes:
  Needing to know the entire P6 grammar isn't mouth watering.

 grammar Grammar::ReqNamed {
 is Grammar::Perl;

Ah, I see. That does answer my question. I had forgotten that grammers can
be inherited from and you can change only the bits you want to change...
thanks.

 Luke

--Abhijit