Dear Monks,

I'm going to try my best not to pose an XY Problem here, but I'm having a tough time coming up with a succinct explanation. Here goes nothing.

I'm working on initialization code for a complex system, with many user- (programmer-)defined levels of nested data structures. The data structure is trivial for a computer to traverse, but making it comprehensible to the programmer is another story. Further, trusting the programmer to initialize it correctly using pure Perl variable syntax would ask for a lot of artificial housekeeping and invite errors, or worse, ambiguity. Fortunately, implementing just a few new simple keywords solves all of these problems (many of them right at compile time) with simple, concise syntax, but having those subs operate on anything less than a file-scoped variable has eluded me. Here's what I've tried/considered:

  1. Pure-OO, using method calls in place of prototyped subs, but this is one of those rare cases where the prototypes are most of the benefit of the expanded syntax.
  2. I wrote a proof-of-concept that uses caller to work on a variable right in the calling namespace, but that's far too likely to cause subtle bugs if someone tries to do anything remotely complex with the initialization code.
  3. Package-scoped variable: In many ways, this is even worse, as it's now essentially a per-thread global for any of the operations.
  4. Closures: Even though the closures can easily be passed a reference and even planted into $caller::, they suffer the same problem as #2.
  5. Source filters: So far the best option, although I'd feel much better finding a simple solution with a little symbol table and prototype hacking, if such a solution exists.
  6. Text parsing: Parsing a scalar (re-inventing Perl, inventing something even more arbitrary, or trying to stuff this problem into a well-known format), would definitely be an anti-pattern in this case, IMO.

Here's the sort of syntax I'm aiming for:

use The::Package;

# sub my_generator(&) is exported by The::Package

my $complex_result = my_generator {
    foo 'bar';
    takes_coderef { ... };
};

foo 'baz'; # Should not affect $complex_result.
           # Ideally, should croak, or not even compile.

[download]

I hope this question makes sense, and has a solution which is much simpler than my explanation. The short, short version of my question is: is there any way to implement prototyped subs that will automatically gain access to a given scalar/ref/object/alias to the same without explicitly passing it in to every call or using the $arrow->notation?)

In reply to Making lexically-scoped ref available to non-OO subs in another package by wanna_code_perl

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