How do you show the type hierarchy of a value?

Question

In Perl5 and Moose, linear isa or linearized isa helps make sense of class hierarchies.

The method WHAT shows the concrete type of a value:

> 42.WHAT
(Int)

How do I show something like

> 42.hypothetical-type-hierarchy
(Int) ┬ is (Cool) ─ is (Any) ─ is (Mu)
      └ does (Real) ─ does (Numeric)

… possibly with further lines for each consumed role?

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edit: example with two strands of roles

class Beta {}
role Delta {}
role Gamma does Delta {}
role Eta {}
role Zeta does Eta {}
role Epsilon does Zeta {}
class Alpha is Beta does Gamma does Epsilon {}

# (Alpha) ┬ is (Beta)
#         ├ does (Gamma) ─ does (Delta)
#         └ does (Epsilon) ─ does (Zeta) ─ does (Eta)

my $ai = Alpha.new
$ai.^mro        # ((Alpha) (Beta) (Any) (Mu))

$ai.^roles      # ((Epsilon) (Zeta) (Eta) (Gamma) (Delta))
                # flat list, not two-element list of a tuple and triple‽

Answer 1

You can query the meta object with

> 42.^mro
((Int) (Cool) (Any) (Mu))

where mro stand for method resolution order and

> 42.^roles
((Real) (Numeric))

You can control which roles are returned via the adverbs :local (exlude roles inherited from parent classes - only available on classes) and :!transitive (exclude roles composed via another role - available on both roles and classes).

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The following should get you started:

my $depth = 0;
for Alpha.^mro {
    say "is {.^name}";
    (sub {
        ++$depth;
        for @_ {
            say '  ' x $depth ~ "does {.^name}";
            &?ROUTINE(.^roles(:!transitive)); # recursive call of anon sub
        }
        --$depth;
    })(.^roles(:local, :!transitive));
}

Given your example code with slight modifications

role Delta {}
role Gamma does Delta {}
role Eta {}
role Zeta does Eta {}
role Epsilon does Zeta {}
class Beta does Gamma {}
class Alpha is Beta does Gamma does Epsilon {}

it produces the output

is Alpha
  does Epsilon
    does Zeta
      does Eta
  does Gamma
    does Delta
is Beta
  does Gamma
    does Delta
is Any
is Mu