How to use metaprogramming to create an enum in Perl 6? - metaprogramming

Question

Given data that represents an enum, such as:
my %enums := {
Color => { red => 0, black => 1, green => 2 },
Status => { fail => 0, pass => 1 }
};
How can I use Metamodel::ClassHOW to create enums equivalent to:
enum Color ( red => 0, black => 1, green => 2 );
enum Status ( fail => 0, pass => 1 );
Timo's ADT library gives an example of how to create a class with ClassHOW, but it doesn't cover enums: https://github.com/timo/ADT/blob/master/lib/ADT.pm6

Answer 1

This seems to do the trick, but it's mostly untested:
my %enums := {
Color => { red => 0, black => 1, green => 2 },
Status => { fail => 0, pass => 1 }
};
my #types = gather {
for %enums.kv -> $name, %values {
my $type = Metamodel::EnumHOW.new_type(:$name, base_type => Int);
for %values -> $pair {
$type.^add_enum_value($pair);
}
$type.^add_role(Enumeration);
$type.^add_role(NumericEnumeration);
$type.^compose;
take $type;
}
}.list;
say #types; # Output: [(Status) (Color)]
Note that this puts the types into a data structure, because lexical scopes are immutable at run time, so you can't declare them just as you would with enum Color ....