Re: Typescript grammar in Bison

[Simon Richter]

Hi,

On 3/22/22 9:24 PM, Ricard Gascons wrote:

> I've been a Bison user for some time now, I've been writing some toy
> projects here and there. I was wondering if there are online resources I
> could find existing grammar from well-known programming languages? Just the
> definitions, not the implementations of course.

> More specifically, I'm looking for an existing Typescript grammar I could
> use for a personal project. I guess Javascript would work too. I've looked
> online and haven't had any luck so far.

I have a beginning of one that accepts the official ECMAScript testsuite 
at least, but there is quite a lot missing both in the grammar and in 
the testsuite.

The main problem with ECMAScript is that in principle it would be 
possible to build an LALR parser for it, but there is no way to express 
this sensibly in Bison, as the definition uses "negative tokens" and 
last-resort parsing extensively.

The "continue", "break", "throw", "return" and "yield" statements have 
an optional expression that can follow, but a newline is not permitted 
at this point, likewise newlines are not permitted before the "=>" token 
in an arrow-function.

This works together with automatic semicolon insertion to accept 
programs with missing semicolons -- the rule is that if a token is 
unexpected, but the parse would be valid if a semicolon was inserted 
before the current token, then the parser should pretend that the 
semicolon was there.

That can be expressed in some, but not all cases, e.g.:

    lexical_declaration:
        "let" binding_list ';'
    |   "let" binding_list

works for me, and I can generate a warning "inserted semicolon" from the 
action of the second list, but this technique doesn't work everywhere a 
semicolon is expected, because that introduces conflicts that are 
technically in another rule, so precedence cannot resolve these.

Feel free to use the attached lexer and parser as a basis. The "NOLT" 
comment indicates places where no line terminator is allowed, this is 
currently not enforced.

   Simon

es.ll.xz
Description: application/xz

es.yy.xz
Description: application/xz

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