From: "Patrick R. Michaud" <[EMAIL PROTECTED]>
Date: Wed, 28 May 2008 23:14:06 -0500
On Wed, May 28, 2008 at 10:05:32PM -0400, Bob Rogers wrote:
> Pos? Named? Reqd? => Example
> yes no yes => .param pmc A
> yes no no => .param pmc B :optional
> yes yes yes => .param pmc C :lookahead('c')
> yes yes no => .param pmc D :optional :lookahead('d')
> no yes yes => .param pmc E :named('e')
> no yes no => .param pmc F :optional :named('f')
>
> I can see why B has to be after A and before C, and I assume ":lookahead
> before :named" makes the implementation easier, but I can't see the need
> for any particular ordering of C vs. D, or E vs. F. Am I missing
> something? Just curious,
C needs to come before D because all required positionals need to be
filled before we get to the optional ones.
But there are two ways to fill a :lookahead positional . . .
================
From: Allison Randal <[EMAIL PROTECTED]>
Date: Thu, 29 May 2008 10:42:31 +0200
. . .
But you can never switch to optional in the positional parameters and
then switch back to required in the lookahead parameters:
.param pmc A
.param pmc B :optional
* .param pmc C :lookahead('c') # syntax error
.param pmc D :optional :lookahead('d')
Hmm. Seems to me that a minimal call to this sub could look like:
foo(1, :c(3));
which (if I haven't butchered the P6 syntax) would bind A to 1 and C to
3, leaving B and D unbound. I don't have a real use case for this,
though.
And agreed that the ordering of the named-only parameters doesn't
really matter, but for code maintenance sanity and possible future
optimizations, let's say that required named-only parameters must
come before optional named-only parameters.
Allison
Sounds reasonable.
-- Bob
