Nearley macros not supported

[kasbah]

I had a go at converting my nearley grammar but I encountered the error:

File "/home/kaspar/.local/lib/python3.5/site-packages/lark/tools/nearley.py", line 116, in _nearley_to_lark
    assert False, directive
AssertionError: include

So I am guessing @include is not supported yet. I also noticed the TODO for macros. Is my assessment correct that includes and macros are not yet supported?

[erezsh]

That is correct! Do you need both? I imagine includes would be easier to add.

[kasbah]

I do make use of both in my grammar, yes. There are always workarounds of course. I think I'll have a go at implementing includes when I get a chance though.

[erezsh]

Cool, let me know if you have any questions, about the code or in general.

[kasbah]

Do you agree that the best way to add macros would be to add support for them in Lark and then translate them?

[erezsh]

That would be my choice as well. Since you are familiar with macros in nearley, can you describe their main properties (i.e. features) ?

[kasbah]

They are simple pre-processor functions with variables, that are expanded to several rules. I added a test case to nearley yesterday that should be a simple example of a macro.

[erezsh]

The way I understand it, there are the following sub-tasks, all in load_grammar.py:

1. Add macro syntax, both definition and usage
2. In GrammarLoader.load_grammar, verify and create macros (also add macros to Grammar object)
3. In Grammar.compile, apply the macros using a transformer

[kasbah]

So, starting with syntax, are you opposed to e.g.:

combine[X, Y]: $X | $Y | $X "/" $Y | $Y "/" $X

[erezsh]

Well, square brackets are already used for optional expressions. But I'm fine with

combine{X, Y}: $X | $Y | $X "/" $Y | $Y "/" $X

[erezsh]

Now that Lark supports templates, this should be a lot easier to do.