Hello, I just finished reading the early module chapter of “Real world Ocaml” and wondered about the rationale behind one of the module design guidelines shared towards the end of the chapter (guideline used apparently in Base and Core): Put t first. If you have a module M whose primary type is M.…

Just for context. In OCaml: type constructors take arguments on the left: int list functions take arguments on the right: print_endline “hello” Functions are usually written to take several arguments (curried) rather than a tuple holding all arguments. Argument order matters when we want to to su…

The convention you quote is really specific to packages from the Jane Street ecosystem like the Base library. The opposite convention is actually more common otherwise (for persistent structures only though, as @lindig noted), for the same reasons given in your link, that it works better for functio…

[image] threepwood: many people do not like to have non-meaningful labels everywhere. Can’t they be meaningful labels?

On Seq.iter ~f:print_int I just can’t see what a meaningful label would be, any label is just adding reading noise.

If I understand correctly, you don’t find the ~f: meaningful? Since Seq.iter takes two arguments, I personally find the ~f: label useful to disambiguate which one of the two is the callback. Perhaps this is because I’m too stubborn to memorize the order of function parameters and don’t believe ther…

[image] smolkaj: Since Seq.iter takes two arguments, I personally find the ~f: label useful to disambiguate which one of the two is the callback. If you need a label to disambiguate between these two arguments then you have a larger problem than that: you are not having meaningful names for y…

thanks @jjb for the link, I’m sorry I basically posted a duplicated question :sweat_smile:

The ~f is likely for “function”. It does seem to be meaningful. And here, it can be used to choose the order of parameters. List.map l ~f:(a long function) or A list computation |> List.map ~f:(a function).

It’s really a question of whether you’re willing to pay the label tax on every function, or if you prefer to reserve labels for situations where confusion could legitimately happen between arguments or important information needs to be carried in the argument name. Whichever convention you choose (f…

[Real world Ocaml] Put t first

Learning

jjb January 21, 2026, 1:27pm 3

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[Real world Ocaml] Put t first

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