Tangential - on the 'use [] instead of <>' advice that you referenced in the post, I wish more languages would experiment with making types first class values that just get passed in regular () braces instead.

With erased static types, you can do arbitrary operations on types-as-values at compile time and just compile the static result into the runtime code, so it doesn't even cost anything at runtime to do this. Generic functions just turn into curried functions with the type params as their first param set.

My wip language uses '()' for 'always explicit params' and '{}' for 'can be implicit params', but both types and values can be passed into both (of course inference only makes sense for statically known types/values, so 'value' params in curly braces must be known at compile time and are treated like singleton types as well as their actual value in runtime code that uses them).

> am I correct assuming you pretty much give up the benefits of a readable grammar as documentation?

This is more of a question language than a parser language. If you have a language that requires a Turing-complete parser than you gave up on grammar. You can use Pratt to parse languages that have grammars.

The language that I'm implementing has procedural macros (hence the parser is Turing-complete). However it has some "structure" that I can port to a tree-sitter parser. The tree-sitter parser for my language won't be 100% accurate, but it'll capture the most important structures.

You need to forbid stuff such as:

  return return 1;

However extending Pratt parsing to handle this case is trivial: https://vinipsmaker.github.io/blog/article/statements-in-pra...

It's still an extension so not really pure Pratt parsing IMO (other practitioners of Pratt parsing disagree with me).

Recursive descent and Pratt are two different but related parsing methods. Pratt is simpler and recursive descent is more explicit, but it's not an "either/or" thing since a parser can use both methods.

I personally think that Pratt is a combination of recursive descent and precedence-climbing. Maybe even the combination? Those ideas are individually older than Pratt.

This is standard CS terminology - if you take a compiler course it'll be explained in the first couple lectures.

The ELI5 is that "semantic actions" are bits of code that a parser generator runs, and "production rules" are patterns that tell it when to run them.

I assume that they refer to what you do when you write a Yacc or Bison file or any other input file for a similar parser generator.

A Yacc file contains the grammar of the language to be parsed, but to each grammar rule you can attach a C function that will be invoked by the generated parser when matching that rule.

That C function is the "semantic action" registered for the corresponding grammar production rule.

For instance, by registering appropriate "semantic actions" the generated parser can become a language interpreter, e.g. when matching a multiplication expression a function that does multiplication is invoked, and so on.

If the parser is intended for a compiler, not for an interpreter, the "semantic actions" may generate some intermediate format of the compiled program, like that used by LLVM.

Others here already answered your question. In the blogpost, the text that immediately follows already demonstrates the concept, then it contrasts to what's done in Pratt parsing (semantic actions to to terminals instead of non-terminals). Non-terminals is another way to refer to production rules. This difference is a pretty big deal so it's important to mention. The rest of the section goes on to explain the consequences of this difference. None of this is mentioned in other Pratt tutorials that I read before so I doubt a slop machine would write articles of Pratt parsing even mentioning this trait at all.

The article doesnt read like slop. And this is a very clear sentence to anybody who knows any amount of parser theory.

"Production rules" are rules in grammar descriptions for tools like yacc. "Semantic actions" correspond to pieces of code/logic executed whenever a given rule is fully parsed from input.

The blog reads like organic human text, not mechanical slop.

The terminology is baroque, but pretty standard in parsing circles.

Essentially, different parsing algorithms "run side effects" at different stages of the parsing algorithm application, which can make certain things easy or difficult depending on the timing.

E.g.: If parsing runs side effects before it has 100% decided on what rules have been applied, it may need to "back track" and undo side-effects. This can be very painful to code around, so a common solution is to build (only) a temporary abstract syntax tree (AST) in a pure functional manner, and later come back and process that instead of trying to handle every "do and undo" scenario during initial parsing.

Parsers that only run side-effects when a decision is final allow very efficient compilers that directly "do the thing" instead of building temporary structures.

IIRC, Pascal was compiled this way, in a single pass.

That is not slop btw

[flagged]