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That's an interesting point, and something I thought of when reading the parser combinator vs. recursive descent point Around 2014, I did some experiments with
by chubot 2y ago
That's an interesting point, and something I thought of when reading the parser combinator vs. recursive descent point
Around 2014, I did some experiments with OCaml, and liked it very much
Then I went to do lexing and parsing in OCaml, and my experience was that Python/C++ are actually better for that.
Lexing and parsing are inherently stateful, it's natural to express those algorithms imperatively. I never found parser combinators compelling, and I don't think there are many big / "real" language implementations that uses them, if any. They are probably OK for small languages and DSLs
I use regular expressions as much as possible, so it's more declarative/functional. But you still need imperative logic around them IME [1], even in the lexer, and also in the parser.
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So yeah I think that functional languages ARE good for writing or at least prototyping compilers -- there are a lots of examples I've seen, and sometimes I'm jealous of the expressiveness
But as far as writing lexers and parsers, they don't seem like an improvement, and are probably a little worse
[1] e.g. lexer modes - https://www.oilshell.org/blog/2017/12/17.html https://www.oilshell.org/blog/2017/12/17.html
- greener_grass 2y agoOCaml allows mutation via reference cells.
- chubot 2y agoI know that, and obviously you can write a recursive descent parser in OCaml But I'm saying there's nothing better about it than doing it in OCaml vs. C++ or Python -- it's the same or a little worse IMW it's natural to express the interface to a lexer and parser as classes -- e.g. you peek(), eat(), lookahead(), etc. Classes being things that control mutation But objects in OCaml seem to be a little separate dialect: https://dev.realworldocaml.org/objects.html https://dev.realworldocaml.org/objects.html When I debug a parser, I just printf the state too, and that is a little more awkward in OCaml as well. You can certainly argue it's not worse, but I have never seen anyone argue it's better. --- Culturally, I see a lot of discussions like this, which don't really seem focused on helping people finish their parsers: https://discuss.ocaml.org/t/why-a-handwritten-parser/7282/7 https://discuss.ocaml.org/t/why-a-handwritten-parser/7282/7 https://discuss.ocaml.org/t/good-example-of-handwritten-lexer-recursive-descent-parser/15672 https://discuss.ocaml.org/t/good-example-of-handwritten-lexe... I also use lexer/parser generators, and I like that there are more tools/choices available in C/Python than in OCaml.