You can't get there from here

"Is my program going to finish?"

For concreteness, let's say we have the source code for a function:

        $CODE = "sub { 
                   my $arg = shift;
                   ... do something with $arg ...
                   ... return some result ...
                   ... (or not) ...
                 }";

And we have some input value:

        $INPUT = "carrots";

We want to know whether the function will ever return, when given argument $INPUT
So we want a function like this:

        sub halts {
          my ($source_code, $input) = @_;
          ... do something clever ...
          ... return true if the function finishes when given '$input'
          ... return false if not
        }