Extracting tokens out of ES6 template literals with Ragel

Question

JavaScript contains the following syntax:

`hello ${name}`

I'm wondering how a Ragel machine would split the syntax above. The way I see it, the type of the closing curly brace depends on the parsing state. For example, in the code below the curly brace is instead part of the string token, since the ${ token isn't there:

`hello name}`

Finally, it becomes more tricky when you consider that the right curly can also be found within the variable expression itself, ie:

`hello ${() => { return name }()}`

How would a similar context-dependent grammar be implemented with Ragel?

Answer 1

The syntax inside of `` is not normally something you would handle with your lexical analyzer. Better to send it to your parser as a sequence of literal text and/or tokens. So you'd send "`" as opening, "hello " as some literal text, then the tokens "(", ")" etc. To know when to stop and go back to literal text you either need some feedback from your parser to to your scanner, or inside the scanner you need to balance the parens.

Note I've never actually made a parser for javascript, just going on what you provided above.