How do I create a perl sub by specifying its parse tree?

Question

Given a CODE ref, is it possible to:

1. Access the parse tree of that CODE ref
2. Create a new CODE ref by specifying the parse tree of the CODE ref which can contain elements of the parse tree returned in ¹

Normally we create subroutines in perl by specifying source code which is then parsed and converted into a parse tree.

I would like to write a perl function which can create a subroutine by specifying its parse tree, and that parse tree could be derived from another parse tree of some other subroutine.

Possible?

Answer 1

I don't know the full answer to your question, but I know that Data::Dumper can deparse a code reference. Looking at its documentation, I see that it uses B::Deparse to do the heavy lifting (the B:: modules are the ones that interact with the compiler). Unfortunately it seems that this only results in a textual representation of the coderef.

Instead I searched for Op on metacpan and got many more interesting possibilities. Since I am now far out of my depth in the deepest Perl magic, I will leave it to you to look over those results. Perhaps something will be useful.

Answer 2

This has nothing to do with opcodes, but it does enclose the same two variables in three different closures. The variables are enclosed within subroutines reminiscent of class get/set routines, and those closed vars are then shared by other closures via their access routine.

This is a response to the comment: I'm sure it will be necessary to access the underlying nodes in the parse tree so that I can create new closures which are closed over the same variables.

use strict;
use warnings;
use v5.14;

# create closed vars
my $v1 = access_closure(6);
my $v2 = access_closure(42);

# play with them
say "v1 ", &$v1;
say "v2 ", &$v2;
say "v1 ", &$v1(5);
say "v2 ", &$v2(43);
say "v1 ", &$v1;
say "v2 ", &$v2;

# create silly closures that use them
my $test1 = test_closure(2);
my $test2 = test_closure(17);
my $test3 = test_closure(50);

# play with those
&$test1;
&$test2;
&$test3;

# create the get/set routine for a closed var
sub access_closure {
    my $val = shift;
    return sub {
        $val = shift if @_;
        return $val;
    }
}

# create a silly closure that encloses a control var and uses the two other vars
sub test_closure {
    my $val = shift;
    return sub {
        say "\nval is $val";
        printf "v1 is %2d, v2 is %2d\n",
            &$v1, &$v2;
        if (&$v1 < $val) {
            say "Increment v1";
            &$v1(&$v1+1);
        }
        if (&$v2 > $val) {
            say "Decrement v2";
            &$v2(&$v2-1);
        }
        printf "v1 is %2d, v2 is %2d\n",
            &$v1, &$v2;
    }
}