Ocaml recursion not printing int when inside another Function

Question

When I compile and Execute this piece of code. It prints nothing.

 let main list = let rec xyz list = match list with |[]->[] |m::body -> begin print_int m; xyz body end in xyz let h = main [1;2;3]

If xyz is used outside of main is working without any error and printing 1 2 and 3

Why would it? You're not running the inner function. I bet you're also getting a warning about an unused value. You should heed that warning and either use the returned value or explicitly ignore it with a type annotation. That would give you a much more useful error. — glennsl
– glennsl, Commented Apr 22, 2021 at 16:51
@glennsl, what command are you using to display all the warnings? — Andrej Hatzi
– Andrej Hatzi, Commented Apr 22, 2021 at 17:35
On the command line, you can use -w +A, if you are using ocamlc or ocamlopt directly. In the file itself adding [@@@warning "+A"] at the top of the file will be equivalent. And Dune has a better set of warning enabled by default. — octachron
– octachron, Commented Apr 22, 2021 at 17:48
The unused-var warning is enabled by default, so you shouldn't need to do anything. Turning on all warnings isn't a bad idea though. Or even -warn-error +A to turn them into errors. — glennsl
– glennsl, Commented Apr 22, 2021 at 17:56
@octachron Ah, I was originally referring to the h variable though, which also does not seem to be used as its type is not what one would expect from the function. — glennsl
– glennsl, Commented Apr 22, 2021 at 20:56

octachron · Accepted Answer · 2021-04-22 16:52:29Z

Compiling your code with all warning enabled yields the following warning:

1 | let main list = ^^^^ Warning 27 [unused-var-strict]: unused variable list.

And indeed, the argument list is unused by main since in

let main list = let rec xyz list = ... in xyz

you are returning the function xyz without applying it.

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