postprocessor functions for terminals/tokens

[coolvision]

Now if I want to postprocess a terminal token, I have to write, for example:

property_value -> number | js_object
number -> %number {% function(d) { return d[0].value; } %}
js_object -> %js_object {% function(d) { return d[0]; } %}

What about allowing to use syntax like:

property_value -> %number | %js_object
%number {% function(d) { return d[0].value; } %}
%js_object {% function(d) { return d[0]; } %}