OCaml Module Naming

Question

I'm trying to get started with OCaml, and I've created a new project with:

dune init project 01_calorie_counting

And that created a sensible enough looking project skeleton:

.
├── 01_calorie_counting.opam
├── _build
│  └── log
├── bin
│  ├── dune
│  └── main.ml
├── dune-project
├── lib
│  └── dune
└── test
   ├── 01_calorie_counting.ml
   └── dune

However, when I cd into the folder and run dune build I get this error:

File "lib/dune", line 2, characters 7-26: 2 |  (name 01_calorie_counting))
           ^^^^^^^^^^^^^^^^^^^ 
Error: "01_calorie_counting" is an 
invalid module name. Module names must be non-empty and composed only 
of the following characters: 'A'..'Z', 'a'..'z', '_', ''' or '0'..'9'. 
Hint: M01_calorie_counting would be a correct module name

So, am I going insane? Last I checked, that name only contains characters in the allowed range.

Is there an additional restriction on it not being able to start with a number that's not listed in the help message?

glennsl · Accepted Answer · 2023-07-23T18:58:14.213

4

Module names must start with a letter, and the first letter will be upper-cased in the module name if the file name starts with a lower-case letter.

See the manual's section on how modules relate to the file system:

The compiler always derives the module name by taking the capitalized base name of the source file (.ml or .mli file). That is, it strips the leading directory name, if any, as well as the .ml or .mli suffix; then, it set the first letter to uppercase, in order to comply with the requirement that module names must be capitalized.

as well as the section on the lexical format of identifiers:

ident               ::=  (letter ∣ _) { letter ∣ 0…9 ∣ _ ∣ ' } 
 
capitalized-ident   ::=  (A…Z) { letter ∣ 0…9 ∣ _ ∣ ' } 
 
lowercase-ident     ::=  (a…z ∣ _) { letter ∣ 0…9 ∣ _ ∣ ' } 
 
letter              ::=  A…Z ∣ a…z

and of object names:

module-name         ::=  capitalized-ident

edited Jul 23 '23 at 18:58

answered Jul 23 '23 at 18:52

glennsl

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Also useful: https://v2.ocaml.org/manual/names.html – Chris Jul 23 '23 at 18:54
Might be worthwhile updating the error message to reflect that? Thank you for the details though! – ScottishTapWater Jul 23 '23 at 18:56
1

Definitely. I'd consider that a bug even. – glennsl Jul 23 '23 at 18:58
1

I might raise a PR on the Dune github when I've managed to at least achieve *something* in this language... – ScottishTapWater Jul 23 '23 at 19:02
Can be fixed here if you're up for it: https://github.com/ocaml/dune/blob/8fe927e61c637356283b4903c445c0740ca2267f/src/dune_rules/site.ml#L5 – glennsl Jul 23 '23 at 19:06
Legend, I'll do that after I've worked out how to get a bloody test project working! – ScottishTapWater Jul 23 '23 at 19:19
Presumably dune init should also refuse to create the project with a numeric first char too – ScottishTapWater Jul 23 '23 at 19:20
https://github.com/ocaml/dune/issues/8252 – ScottishTapWater Jul 23 '23 at 19:24
The rule for the library creation is in `src/dune_lang/lib_name.ml`... Do Libraries also have to start with a letter or is that just Modules? – ScottishTapWater Jul 23 '23 at 19:44
I don't think library names have any connections with module names, so should be fine. – glennsl Jul 23 '23 at 20:24

OCaml Module Naming

1 Answers1