working on a haskell compatible algebraic datatype module for perl6

ADT.pm6

module ADT;

package EXPORT::DEFAULT { };

grammar hs_adt {
    has @.typevars;
    rule TOP {
        $<name>=(<ident>) <params> '=' <definers>
    }
    rule params {
        '[' ~ ']' [ '::'$<typevar>=<.ident> { @.typevars.push($0) }]+ % ',' |
    }
    rule parameters {
        '[' ~ ']' [$<typevar>=<.ident> { $0 ~~ @.typevars }]+ |
    }
    rule definers {
        [ <definition> ]+ % '|'
    }
    rule definition {
        $<constructor>=<.ident> [ $<typedecl>=<.ident> <parameters> ]+ % ','
    }
}

#sub create_adt(@structure) {

#}

use Test;

ok hs_adt.parse("Tree = Branch Tree, Tree | Leaf Str");
ok hs_adt.parse("Tree[::A] = Branch Tree[A], Tree[A] | Leaf A");
ok hs_adt.parse("Either[::A, ::B] = Left A | Right B");