3 ms·

I suspect is not that bad to force to group things manually (1 + (....)) but is truly precedence the biggest issue? I think even without that hand-coded parsers

by mamcx 6y ago

I suspect is not that bad to force to group things manually (1 + (....)) but is truly precedence the biggest issue? I think even without that hand-coded parsers are still superior for error reporting and other factors?

jraph 6y ago
I just wrote a parser in TypeScript that parses itself (for fun, and not quite done yet). Precedence and associativity is a painful aspect of parsing JavaScript… and probably C, Java and many programming languages that look like C. It took me a non negligible part of the time to think about how to handle this. With the presence of infix, suffix and prefix operators, and weird operators like new…(), ? … : …, and a lot of rules and exceptions, it's a lot of fun (for instance, yield is an operator in JavaScript. It takes an optional expression. However, 1 + yield is forbidden…). The grammar of JavaScript expressions is… not simple. And then, you have Automatic Semicolon Insertion, which forces you to backtrack and snapshot / restore the lexer state when consuming white characters EVERYWHERE (well, not literally everywhere, but still) because things may behave differently if there is a new line. And of course, new lines cannot happen in some constructs (there are a few exceptions to the general behavior of ASI), so you need to take care of this too. And then you have the comma operator that is allowed in some places taking an expression (especially in older constructs, and disallowed in other places (especially in newer constructs). So you need to handle this too. Parsing the rest is easy. It's just that there are a lot of things in the language so it's a bit long to write.
- mamcx 6y ago
  Even with pratt parsing? Or using other method?
  - masklinn 6y ago
    I can only expect an other method as both are trivial using a pratt parser (though right-associativity still feels a bit weird).
    - jraph 6y ago
      Indeed, I wrote it by hand, the naive way.

by mamcx 6y ago

jraph 6y ago

I just wrote a parser in TypeScript that parses itself (for fun, and not quite done yet). Precedence and associativity is a painful aspect of parsing JavaScript… and probably C, Java and many programming languages that look like C. It took me a non negligible part of the time to think about how to handle this. With the presence of infix, suffix and prefix operators, and weird operators like new…(), ? … : …, and a lot of rules and exceptions, it's a lot of fun (for instance, yield is an operator in JavaScript. It takes an optional expression. However, 1 + yield is forbidden…). The grammar of JavaScript expressions is… not simple. And then, you have Automatic Semicolon Insertion, which forces you to backtrack and snapshot / restore the lexer state when consuming white characters EVERYWHERE (well, not literally everywhere, but still) because things may behave differently if there is a new line. And of course, new lines cannot happen in some constructs (there are a few exceptions to the general behavior of ASI), so you need to take care of this too. And then you have the comma operator that is allowed in some places taking an expression (especially in older constructs, and disallowed in other places (especially in newer constructs). So you need to handle this too. Parsing the rest is easy. It's just that there are a lot of things in the language so it's a bit long to write.

mamcx 6y ago
Even with pratt parsing? Or using other method?
- masklinn 6y ago
  I can only expect an other method as both are trivial using a pratt parser (though right-associativity still feels a bit weird).
  - jraph 6y ago
    Indeed, I wrote it by hand, the naive way.