anchor.diff:  -export([string/1]).
   -include("reia_nodes.hrl").
   -define(line(Node), element(2, Node)).
  +-define(op(Node), element(1, Node)).
   -define(identifier_name(Id), element(3, Id)).
   
   %% Parse a given string with nicely formatted errors
  
positive.code: mult_expr -> mult_expr mult_op pow_expr :
  #binary_op{
    line=?line('$1'),
    type=op('$2'),
    left='$1',
    right='$3'
  }.
  
negative.code: pow_expr -> pow_expr pow_op unary_expr :
  #binary_op{
    line=?line('$1'), 
    type=?op('$2'), 
    left='$1', 
    right='$3'
  }.
  