S5: grammar compositions
I was rereading S5, and the example of grammatical inheritance caught my
eye:
grammar Letter {
rule greet :w { [Hi|Hey|Yo] $to:=(\S+?) , $$}
...
}
grammar FormalLetter is Letter {
rule greet :w { Dear $to:=(\S+?) , $$}
...
}
My first reaction was that we need a bit more factoring here. I assume we
could do:
grammar Letter {
rule greet :w { greet_word $to:=(\S+?) , $$}
rule greet_word { [Hi|Hey|Yo] }
...
}
grammar FormalLetter is Letter {
rule greet_word{ Dear }
...
}
Will the :w do the right thing here?
My second though was that inheritance might be overused here. My refactoring
was the template method pattern. How would I use a strategy instead. I
know I can define a rule that accepts a parameter, but if I did that then
I'd need to pass that parameter all the way down the tree. Is it possible to
write something like
$letter =~ /(Letter but greet_word(rule :w { Guten Tag })).text;
?
Dave.
Re: S5: grammar compositions
Dave Whipp writes:
grammar Letter {
rule greet :w { greet_word $to:=(\S+?) , $$}
rule greet_word { [Hi|Hey|Yo] }
...
}
grammar FormalLetter is Letter {
rule greet_word{ Dear }
...
}
Will the :w do the right thing here?
In the new S5 revision, :w changed from static to dynamic. :w is about
the text now, not the rules. So, yes, it will.
My second though was that inheritance might be overused here.
Perhaps, perhaps not. In the multimethod paper that's coming soon (it's
turned out to be a lot more than just a multimethod paper; more of an
object model paper), inheritance may become much more useful than it
once was, at least in an abstract sense. In particular, subtypes can be
a form of inheritance in the system. And the best part is that we don't
have to change anything from S12 to apply the model.
But that's beside the point. I just had to give all y'all a little
preview.
It's my suspicion that the template method pattern is often going to be
the right thing to do in rules.
My refactoring was the template method pattern. How would I use a
strategy instead. I know I can define a rule that accepts a parameter,
but if I did that then I'd need to pass that parameter all the way
down the tree. Is it possible to write something like
$letter =~ /(Letter but greet_word(rule :w { Guten Tag })).text;
Hmm... this pattern seems a lot kludgier for this situation. You could
use a parameterized grammar, I suppose:
grammar Letter[?$greeter = / [Hi|Hey|Yo] /] {
rule greet :w { $greeter $to := (\S+?) , $$ }
}
Which may be a better solution if you're expecting a lot of different
types.
By the way, you can't say:
$letter ~~ /( ...
Because ( starts a conditional assertion. The usage becomes:
$letter ~~ /Letter[/:w Guten Tag /].greet/
Luke
Re: S5: grammar compositions
Grammar roles? Larry
S5: array interpolation
An interpolated array:
/ @cmds /
is matched as if it were an alternation of its elements:
/ [ @cmds[0] | @cmds[1] | @cmds[2] | ... ] /
As with a scalar variable, each one is matched as a literal.
Like this? (Assuming single quotes don't interpolate @foo[...])
@a = ('a', 'b', 'c');
'@a[0]' ~~ m:/ @a /; # true
'@a[2]' ~~ m:/ @a /; # true
'@a[9]' ~~ m:/ @a /; # false
If so, that seems pretty wacky...
-John
Re: S5: array interpolation
John Siracusa [EMAIL PROTECTED] wrote:
An interpolated array:
/ @cmds /
is matched as if it were an alternation of its elements:
/ [ @cmds[0] | @cmds[1] | @cmds[2] | ... ] /
As with a scalar variable, each one is matched as a literal.
Like this? (Assuming single quotes don't interpolate @foo[...])
@a = ('a', 'b', 'c');
'@a[0]' ~~ m:/ @a /; # true
'@a[2]' ~~ m:/ @a /; # true
'@a[9]' ~~ m:/ @a /; # false
I think he means as opposed to a subrule. In Perl 5 terms, there's
an implicit \Q\E around each value in the array.
--
Brent 'Dax' Royal-Gordon [EMAIL PROTECTED]
Perl and Parrot hacker
There is no cabal.
[I currently have a couple Gmail invites--contact me if you're interested.]
[S3, S4, S5]: =~ becomes ~~
I know that, you know that ... but the synopses never actually say it. It's evident from context, but it's never said explicitly. I would *think* that should be in the Operator renaming section of S3, and presume this is an oversight? -- Schwäche zeigen heißt verlieren; härte heißt regieren. - Glas und Tränen, Megaherz
Re: [S3, S4, S5]: =~ becomes ~~
Herbert Snorrason writes: I know that, you know that ... but the synopses never actually say it. It's evident from context, but it's never said explicitly. I would *think* that should be in the Operator renaming section of S3, and presume this is an oversight? Okay, it ought to be there soon. I added it in the New operators section, since it's pretty different from =~. Arguably the ~~ table should go in S3 instead of S4. Luke
Re: S5: grammar compositions
On Wed, 2004-09-15 at 12:47, Larry Wall wrote: Grammar roles? It seems sensible, having said Here's a better method of type checking and code re-use and Here's a generalization of pattern matching to make it more like programming. Not doing it would be like making closures that can't write to the closed-over variables. That's just crazy! -- c
