问题
I wrote a test program, and now it seems that if I don't use $/
in a
method signature because I have to use .match inside the method, I can no long make anything. What did I do wrong?
A further question is that if .match
sets $/
, and $/
is read-only, then I cannot have $/
in the signature of a method that contains a .match
statement, and I cannot have more than one .match
inside the method because each .match
will try to set the read-only $/
. This will be very awkward to program.
Here is the test program with only one .match
statement inside and the results:
The test program:
grammar test {
regex TOP { <foo><bar> }
regex foo { :i \s* foo \s* }
regex bar { :i \s bar \s* }
}
class actTest {
method foo ($x) { # program fails if I use $/ in signature
print "1 "; say $x; # how to combine the 2 and show $x as match?
print "2 "; say $x.WHAT;
my $newStr = $x.Str;
print "3 "; say $newStr;
my $newMatch
= $newStr.match(/:i(f)(oo)/); # adverb cannot be outside?
print "4 "; say $newMatch.WHAT;
print "5 "; say $newMatch;
print "6 "; say $/;
my $oo = $newMatch[1].Str;
print "10 "; say $oo;
my $f = $newMatch[0].Str;
print "11 "; say $f;
my $result = $oo ~ $f;
print "12 "; say $result;
make $result; # now I cannot make anything; huh???
}
method TOP ($/) {
print "8 "; say $<bar>;
print "9 "; say $<foo>.made; # failed, method 'foo' makes nothing
make $<bar> ~ $<foo>.made;
}
}
my $m = test.parse("Foo bar", actions => actTest.new);
print "7 "; say $m;
And the results:
1 「Foo 」
2 (Match)
3 Foo
4 (Match)
5 「Foo」
0 => 「F」
1 => 「oo」
6 「Foo」
0 => 「F」
1 => 「oo」
10 oo
11 F
12 ooF
1 「Foo」
2 (Match)
3 Foo
4 (Match)
5 「Foo」
0 => 「F」
1 => 「oo」
6 「Foo」
0 => 「F」
1 => 「oo」
10 oo
11 F
12 ooF
8 「 bar」
9 (Any)
Use of uninitialized value of type Any in string context.
Methods .^name, .perl, .gist, or .say can be used to stringify it to
something meaningful.
in method TOP at matchTest.pl line 28
7 「Foo bar」
foo => 「Foo」
bar => 「 bar」
回答1:
1) How to make
without $/
make ...
is just a shortcut for $/.make(...)
.
If you want to affect a different Match
object than the one stored in $/
, you have to use the method form directly, i.e. in your case $x.make($result)
.
2) When and why $/
is read-only
By default, $/
is bound to a normal item container (like a variable declared with my
), i.e. not read-only. So there shouldn't be any problem with using the .match
method multiple times in a routine.
It's only when you explicitly declare $/
as a parameter in a routine signature, that $/
will be bound directly to the Match
object passed to that routine (not wrapped in an item container), and will thus be read-only inside the routine – because that's how normal signature binding works.
You could use the is copy
trait to override the normal read-only parameter binding, and force $/
to be a mutable item container inside the routine:
method foo ($/ is copy) { ... }
This way, using .match
inside the routine would work, and would store a new Match
object in $/
. But then you wouldn't have access to the original Match
object passed to the routine anymore, and thus couldn't affect it with make
. So for an action method that needs to use .match
, using a custom parameter name like you did is the way to go.
来源:https://stackoverflow.com/questions/41027321/perl6-grammar-actions-unable-to-make-anything-if-not-using