Jane Street Base changes the semantics of String.concat on my MacOS system

Learning
1

Hello,

I am trying to learn OCaml and I have installed the binary OCaml-5.3.0 distribution on my MacOS where “uname -a” gives

Darwin Kernel Version 20.6.0: Thu Sep 29 20:15:11 PDT 2022; root:xnu-7195.141.42~1/RELEASE_X86_64

I have also installed Jane Street’s Core library using “opam”.
When I try to compile and run this program (“dune exec bad”)

open Base
let lines = ["aa"; "bb"; "cc"]
let text = String.concat "\n" lines;;
print_endline text

with the following Dune file

(executable
 (public_name bad)
 (name main)
 (libraries base))

then I get the error message

File "bin/main.ml", line 3, characters 30-35:
3 | let text = String.concat "\n" lines;;
                                  ^^^^^
Error: The function applied to this argument has type ?sep:string -> string/2
This argument cannot be applied without label

“dune exec bad” succeeds after changing “open Base” to “(* open Base *)”

Trying to change lines into an array of strings and using Jane Street’s String.concat_array leads to a similar error message.

Thanks

2

Well if you open Base in your code then your String module is Base.String instead of Stdlib.String and the signature of Base.String.concat is different from Stdlib.String.concat.

3

Jane street libraries make heavy use of labeled arguments: Labelled and Optional Arguments · OCaml Documentation

So the API isn’t exactly the same when comparing to the “pervasive” standard library.

Basically just add a tilde in front of your list variable :slight_smile:

4

When I add a tile in front of the “lines” list variable, I get

File "bin/main.ml", line 3, characters 31-36:
3 | let text = String.concat "\n" ~lines;;
                                   ^^^^^
Error: The function applied to this argument has type ?sep:string -> string/2
This argument cannot be applied with label ~lines
5

He mixed up, he meant in front of the separator:

let text = String.concat ~sep:"\n" lines
1 Like
6

Thanks a lot, it works now after adding “open Stdio” to ensure the use of Jane Street’s version of “print_endline”.