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Postings from July 2005
HaloO Jonathan,
you wrote: (why off-list?)
>>Hmmmm, and the current actor/owner is $/ which gives the expanded
>>method call syntax:
>>
>> .method # really means: $/.method($_)
>
>
> You mean $?SELF rather than $/. $/ is now the match object used in
> rules.
I would say *for* rules/methods. $?SELF is a variable that is bound for
the body of the rule/method once. But I'm talking about the outside
general environment. I'm unsure about the rule syntax but wasn't it like
grammar Foo
{
rule alpha {...}
rule beta {...}
rule blahh { <{ if .alpha { say "letters $/" } }> <beta> }
} # ^^^^^^^
I wonder how the generic, lexically scoped invocant/owner is called.
I propose to call it $/ and let the former topicalizer become
block owners and $_ the block topic that flows into blocks from
further outside if not explicitly bound with -> like:
$topic := Some.new;
$_ := $topic;
for @objects { .action } # call on $/ from @objects with $_ := $topic
# in all loops
@objects».action; # same for single action syntax
# but
for @objects -> { .action } # means $/.action($/) because
# $_ bound to dynamic block owner;
# but usefull for methods that don't
# use the topic, in particular accessors
# and mutators
# same as sub call
for @objects -> { action } # means action($/) because $_ := $/
# but $/ is there if action is of
# type Method
The only drawback I see is, that the careless method programmer could be
caugth in an endless .action loop if .action invokes .action explicitly
on $_ where $_ := $/ from the outside. The same endless loop could of
course be achieved with a free standing .action but that looks more like
intention.
With the lurking pitfalls an occasional check of $_ =:= $?SELF and
$/ =:= $_ seems advisable and indicates that the invocant wasn't
exchanged midway :)
Same with other topicalizers
given $x {...} # topic untouched, but $/ := $x
given $x -> {...} # $_ := $x as well
But
if $x {...} # $/ and $_ untouched
if $x -> {...} # $_ := $x (non boolean value)
One more interessting thing is that in exception handlers all three
variables $!, $/ and $_ are in scope. This might allow to resume where
the exception occurred after the cause was fixed e.g. by loading or
generating some code, some revamping or other &DEEP_MAGIC.
> Always needs parens? Even in the simple cases?
>
> my $foo = $cond ?? $alpha :: $beta;
People who know the parsers better than I do, correct me but I want
this to tokenize as (my $foo = $cond)??($alpha)::($beta) and then
given to the current match state of the parser seperately to produce a
"name lookup" resulting in the above case in three code snippets.
This e.g. allows to define the boolean "type" as
*::false ::= *::bit::0;
*::true ::= *::bit::$_??$_::*false;
or so. And whitespace around ?? and :: doesn't matter!
?? just means skip next lookup if "lookup" fails.
Regards,
--
TSa (Thomas Sandlaß)
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