method numeric($/) { make +$/ }
#                         ^  convert to a number

# propagate the number as the AST:
method lhs($/) { make $<numeric>.ast }
method rhs($/) { make $<numeric>.ast }


method expression($/) {
   my $value = $<lhs>.ast;

   # iterate over all matches of the first (...) group
   for $0.list -> $m {
       $value = %actions{$m<op>.ast}.($value, $m<rhs>.ast);
   }
   make $value;
}