code: function locToString(loc) {
      return match(loc, function(when) {
          when({
              start: { line: match.var('sl'), column: match.var('sc') },
              end: { line: match.var('el'), column: match.var('ec') }
          }, function(vars) {
              return " at " + vars.sl + ":" + vars.sc + "-" + vars.el + ":" + vars.ec;
          });
  
          when(match.any, function() {
              return "";
          });
      });
  }
docs: (Loc) -> str