For a work problem I encountered yesterday, it occurred to me that it'd be trivial to solve with the right helper module. I can't work out if that module is easy, hard or impossible to write - or has already been written.

I'm slightly fuzzy on the details, but I imagine it looking something like this:

% cat myprog
use Data::Annotate;  # 'Tie::Annotate'?
sub adder { return $_[0] + $_[1] }
my($foo, $baz) = (2, 5);
annotate($foo, 'foo');
my $bar = adder($foo, $baz);
say "bar is ", $bar;
say "bar is annotated as ", annotation($bar);
say "bar is derived from ", derivation($bar);
# not sure if that should also attempt to show derivation of the
# components; maybe it should take a maxdepth argument:
my $etc = $bar + $foo;
say "etc is annotated as ", annotation($etc);
say "etc is derived from ", derivation($etc, depth => 3);

% perl myprog
bar is 7
bar is annotated as foo + 5
bar is derived from foo + 5 at myprog line 2
        main::adder(2, 5) called at myprog line 5
etc is annotated as (foo + 5) + foo
etc is derived from (foo + 5) + foo at myprog line 11
        (foo + 5) at myprog line 2
                main::adder(2, 5) called at myprog line 5
        foo annotated at myprog line 4
%
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An obvious difficulty is how to construct the annotation string for various ops, but I'd be happy enough if it said "i_add(i_add(foo, 5), foo)" instead.

I'd welcome your thoughts.

Hugo