Comment by pansa2 | Hacker News Reader

Comment by pansa2 | Hacker News Reader

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> TypeScript, Swift, Kotlin, and Scala take string interpolation to the furthest extreme of encouraging actual code being embedded inside strings. So to highlight a string, one must count curly brackets and maintain a stack of parser states.

Presumably this is also true in Python - IIRC the brace-delimited fields within f-strings may contain arbitrary expressions.

More generally, this must mean that the lexical grammar of those languages isn't regular. "Maintaining a stack" isn't part of a finite-state machine for a regular grammar - instead we're in the realm of pushdown automata and context-free grammars.

Is it even possible to support generalized string interpolation within a strictly regular lexical grammar?

Complicated interpolation can be lexed as a regular language if you treat strings as three separate lexical things, eg in JavaScript template literals there are,

    `stuff${
    }stuff${
    }stuff`

so the ${ and } are extra closing and opening string delimiters, leaving the nesting to be handled by the parser.

You need a lexer hack so that the lexer does not treat } as the start of a string literal, except when the parser is inside an interpolation but all nested {} have been closed.

> Is it even possible to support generalized string interpolation within a strictly regular lexical grammar?

Almost certainly not, a fun exercise is to attempt to devise a Pumping tactic for your proposed language. If it doesn’t exist, it’s not regular.

https://en.m.wikipedia.org/wiki/Pumping_lemma_for_regular_la...

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