Separate rules in different EmbeddedActionsParser

[sveri]

Hi,

For separat of logic I would like to split one EmbeddedActionsParser into multiple ones.
I tried to just create another parser extending EmbeddedActionsParser and calling the declared rule from the main parser, but I get an error similar to this:
Error: Parser Definition Errors detected:
Invalid grammar, reference to a rule which is not defined: ->method<-

I wonder if what I want to do is possible at all? I don't care about reuseability, I just want to split my 1000 lines file into multiple smaller ones, grouped by topic.

[bd82]

It would probably be easier to split up the code that defines the rules into multiple files and invoke the multiple rule definitions helpers
during a single parser's constructor.

See example in a large productive parser (Java)

• invoking rule definition helpers: https://github.com/jhipster/prettier-java/blob/3dfeef40ac3df34ce01a03b5c9db23d0347079a2/packages/java-parser/src/parser.js#L62-L71
• Parser parts: https://github.com/jhipster/prettier-java/tree/3dfeef40ac3df34ce01a03b5c9db23d0347079a2/packages/java-parser/src/productions

This approach is made possible because Chevrotain is "just JavaScript" so you have a-lot of flexibility in how you mix/match/assemble it.

[sveri]

Thank you for that example, all in all that looks good, but it seems like that approach won't work in typescript? Especially referencing rules that are defined in a different file?

[bd82]

In theory TypeScript should support all JavaScript approaches, as TypeScript is purely a design time tool.
From a practical perspective the question is often how to "explain" the runtime structure to the TypeScript compiler...

This scenario is similar to mix-ins so you could:

1. declare a combined type of all the rules.
2. Use "This Type" inside your rules implementations that leverages the combined type defined earlier.

What I am unsure of is how you would auto-magically obtain the signatures for each sub-set of your rules.
But it may be possible TypeScript will defer it if you assign those rules to some JSONish object structure, e.g:

• TypeScript playground example

Another reference: I used an home brewed mix-in variant to split a large class (not parser) into multiple parts in this repo:

• Relevant docs: https://github.com/Chevrotain/chevrotain/tree/master/packages/chevrotain/src/parse/parser/traits

[sveri]

Thank you very much for the reply. I gave both things a try and I think for me it's best to combine typescript with a pure javascript chevrotain parser, that can be separated into different modules.