«Erlang::Parser::Node::Atom» in «Erlang::Parser::Node::Atom->new(atom => 'xyz');» is just a string literal. It can be any expression that produces the string «Erlang::Parser::Node::Atom» (although you might need parens around some expressions because -> binds rather tightly).

my $class = "Erlang::Parser::Node::$type";
$class->new(@args)
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or even

"Erlang::Parser::Node::$type"->new(@args)
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Altogether:

sub new_node {
   my $kind = shift;
   return "Erlang::Parser::Node::$kind"->new(@_);
}
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