procedural macro to generate pratt parser at compile time #3

sergeyt · 2020-05-08T08:47:33Z

@matklad thanks for wonderful examples of pratt-style parsers

wondering if you have time to generalize it further :)

here is an idea of an declarative way to make expression parsers in no time:

enum UnaryOp {
  #[prefix(1)]
  Plus,
  #[postfix(1)]
  Percent,
  // ...
}

enum BinaryOp {
  #[binary(1, 1)]
  Add,
  #[binary(2, 2)]
  Multiply,
  // ...
}

enum Expr {
  #[primary]
  String,
 #[binary]
  BinExpr(BinaryOp, Box<Expr>, Box<Expr>),
  //  ...
}

// how to invoke parser
let expr = Expr::parse(Token::lexer());

i.e. you just define binding power for operators and define expression categories.

actually the idea is inspired by logos which provides declarative way to generate lexers

I know there are several attempts to do that, but they are still verbose IMO :)

sergeyt · 2020-05-08T12:57:30Z

@maciejhirsz you might be interested :)

matklad · 2020-05-08T13:13:14Z

Not sure if it is an interesting point on a tradeoff curve. If I am willing to stomach code generation anyway, using [G]LR or at least a proper external grammar DSL seems like a better idea. The main appeal of Pratt parseing to me is that you don't need any extra tools to do it :-)

sergeyt · 2020-05-08T13:51:01Z

@matklad I know it does not sound super interesting :). there are a bunch of expression-like languages like Excel, DAX, RDL, etc with little differences. As usual it would be nice to have, but adapting code of this repo is faster approach for now

maybe @segeljakt (author of pratt) might be interested to implement such declarative approach :)

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procedural macro to generate pratt parser at compile time #3

procedural macro to generate pratt parser at compile time #3

procedural macro to generate pratt parser at compile time #3

procedural macro to generate pratt parser at compile time #3

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