Hi, OCaml beginner here. I’m coming from Rust, which has some syntactic sugar/quality of life features around pattern matching and errors. I’m curious what the idiomatic equivalents are for OCaml? Early return Basically, if you have an error, you can return early: let file = match fs::read("hello.…

Generally speaking, none of these exist in OCaml. Some of them have been considered over the years, but did not gather enough consensus to be merged. “Early return” can be simulated using exceptions or monadic operators, but there isn’t anything built-in. Regarding “if let”: see the discussion add…

[image] NicholasLYang: todo! This one does have an analog: assert false (or Stdlib.exit). Cheers, Nicolas

[image] NicholasLYang: Let…else Unless I am missing something, let p = e1 else e2 can be written in OCaml: match e with p -> e1 | _ -> e2 Cheers, Nicolas

Does assert false have a type that can be unified with any other type? That’s what makes todo! special, you can do something like: let i = match parse() { Expr::Int(i) => i, _ => todo!() } And it will type check. For let...else, the else branch is guaranteed to diverge, i.e. return, panic, or…

[image] NicholasLYang: Does assert false have a type that can be unified with any other type? Yes. Cheers, Nicolas

I’d generally do failwith "todo" over assert false. Otherwise you should probably do assert false (* TODO *) to differentiate from an assert false which is meant to fill in an impossible case.

let p = e1 else e2 is an abomination. A truly grotesque and disgusting abuse of language.

[image] NicholasLYang: Early return Basically, if you have an error, you can return early: let file = match fs::read("hello.txt") { Ok(file) => file, Err(err) => return Err(err) }; let file = fs::read("hello.txt")?; I usually use the bindings operators when I need to chain Result in…

[image] NicholasLYang: let file = match fs::read("hello.txt") { Ok(file) => file, Err(err) => return Err(err) }; let file = fs::read("hello.txt")?; You do not need early return for the first one. Yes you can use let*, but its not even needed. The following is fine : match open_in "…

Thanks for the suggestion! To be frank, I’d prefer to keep using ocamlformat than to have this slightly less indented code. Besides, the indentation does seem to serve a visual purpose of indicating the branch taken. Otherwise it’s possible to accidentally read that code as unconditional. Plus in m…

Pattern matching syntactic sugar

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nojb April 15, 2025, 5:40pm 3

This one does have an analog: assert false (or Stdlib.exit).

Cheers,
Nicolas

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Pattern matching syntactic sugar

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