add code config option to enable alternative rule DSL

[kristianmandrup]

This little tweak will allow for alternative DSLs where the resulting rule code and the string generated can differ.

// could be generated by DSL
let selectClauseStr = `() => {
    this.CONSUME(Select)
    this.AT_LEAST_ONE_SEP({
        SEP: Comma, DEF: () => {
            this.CONSUME(Identifier)
        }
    })
}`

export class SelectParser extends Parser {
  registry = {}

  constructor(input) {
    super(input, allTokens)
    this.rules()

    // must be called at the end of the constructor!    
    Parser.performSelfAnalysis(this)
  }

  rules() {
    let def = {
      SEP: Comma,
      DEF: () => {
        this.CONSUME(Identifier)
      }
    }

    let execRule = () => {
      this.CONSUME(Select)
      this.AT_LEAST_ONE_SEP(def)
    }

    this.selectClause = this.RULE("selectClause", execRule, {
      // using code string override to make regExp parser work!
      code: selectClauseStr
    })

    this.selectStatement = this.RULE("selectStatement", () => {
      this.SUBRULE(this.selectClause)
    })
  }

Already tested and works with my DSL experiment in red-dragon :)

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[bd82]

I like the concept.

But not the reliance on strings.
This means that any custom API must also generate strings compatible with the original API.
This is not a very robust approach.

Instead I would go with a more generic approach:

• modify the Parser's config object (passed at construction) not each Rule's config object.
  to accept a custom function that given some params (rule name / rule impel func/ ...) will create the GAST structure.
• By default it will use the built in GAST Builder.
• Custom use cases can implement their own logic, but won't have to be forced to generate strings.

[bd82]

From code review perspective:

• 100% code coverage is mandatory, so if you add a new code branch a new test must also be added.
• Your IDE auto formatted the whole file, please only commit your changes 😄
• An example (in examples/parser) directory could be nice, but not mandatory.

[kristianmandrup]

Cool, sounds great :)

Yeah well, using strings was the easiest approach since I don’t know the internals of the GAST model. I would much welcome a mixed approach,
where the code option is allowed as an override but where the recommended approach is to use a custom GAST builder!

Would love to see a minimal example of this next week!

Cheers! Kristian

PS: Just managed to make the DSL example work with my String based approach for now

[bd82]

I would much welcome a mixed approach.

There is no need for a mixed approach.
If the GastBuilder string --> gast method is exposed.
Than a single generic function on the parser level can perform the conversion from
a string you generated to the GAST using some ID (ruleName).

Would love to see a minimal example of this next week!

You would if you code it 😄
This is a nice to have feature, but not a high priority.
unfortunately I have some higher priority items:

• CST Visitor + Docs
• POCing using Chevrotain in the CoffeeScript compiler

So it would take a while before I get around to this...

[kristianmandrup]

Excited to see what you come up with next. I have this rule DSL for now.

Will look into CST/GAST next.
Cheers!

[bd82]

new CST related capabilities (CST Visitor) will be available in a day or two.
It will make working with CST much easier. 😄

I'll look into these extensibility options in a week or two...
It nice that ppl can create "plugins" to Chevrotain to customize something so internal as
the DSL itself. 👍

[bd82]

I will attempt to implement an official GAST --> Chevrotain DSL transformer.
This will be the basis of supporting both a built-in Combinator API (probably similar to myna's APIs) and to enable users to create their own custom APIs for Chevrotain.

Relevant issue: #480

This could even enable using Chevrotain as a parser generator 😄

This is a huge issue. But the first thing on the agenda is the
** GAST --> Chevrotain DSL transformer. **
Which should at least enable your custom API.

[kristianmandrup]

AweZome!