Actions and Grammars: a proposal for combining them

gistfile1.txt

role EXPRish is Parser {}
grammar EXPR does EXPRish {
  rule TOP { <expr> }
  rule expr { <num> '+' <num> | <num> }
  token num { (\d+) }
}
class EXPR::Actions does EXPRish {
  action TOP { make $<expr>.ast }
  action expr {
    if $<num>.elems == 1 {
      make $<num>[0].ast;
    } else {
      make { :op<+>, :lhs($<num>[0].ast), :rhs($<num>[1].ast) }
    }
  }
  action num {
    make { :literal, :integer, :value(+$0.Str) }
  }
}

EXPR.parse("1 + 2", :actions(EXPR::Actions));