Feature idea: template functionality for rules

I am fairly new to this whole grammar thing, so please forgive me if I am missing something.

I think that adding some kind of template-functionality to lark would be a good idea to avoid redundancy in rules and to increase readability. A template would be a rule that takes parameters. Such a template could then be instantiated into a new rule by giving concrete values to these parameters. A grammar that contains templates could then be transformed into a grammar without templates by instantiating all used template rules.

For example, consider this grammar with templates

spaced(content): " " content " "
r1: "+" spaced("hello")
r2: "-" spaced("world")

spaced is a template that takes a parameter content. spaced("hello") and spaced("world") would be concrete instances of spaced. In a pre-processing step, the grammar can then be transformed into a grammar without templates:

spaced_0: " " "hello" " "
spaced_1: " " "world" " "
r1: "+" spaced_0
r2: "-" spaced_1

[graps1]

Cool, so if it isn’t a problem, I could give it a try in the coming weeks or so.

[erezsh]

This feature has been implemented, so I consider this issue closed. Good job everyone!