# Difference between files beginning with upper or lower case

**URL:** <https://discuss.ocaml.org/t/difference-between-files-beginning-with-upper-or-lower-case/3116>\
**Category:** Learning\
**Created:** [December 31, 2018, 11:01am UTC](https://discuss.ocaml.org/t/difference-between-files-beginning-with-upper-or-lower-case/3116 "2018-12-31T11:01:30Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cmxa](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cmxa/32/1258_2.png) [@cmxa](https://discuss.ocaml.org/u/cmxa)\
**Post date:** [December 31, 2018, 11:01am UTC](https://discuss.ocaml.org/t/difference-between-files-beginning-with-upper-or-lower-case/3116/1 "2018-12-31T11:01:30Z")

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What is the difference between files beginning with upper and lower case?

For example, in the Menhir source – [https://gitlab.inria.fr/fpottier/menhir/tree/master/src](https://gitlab.inria.fr/fpottier/menhir/tree/master/src) – some files begin with upper case and some with lower case.

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**Author:** ![lindig](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lindig/32/532_2.png) [@lindig](https://discuss.ocaml.org/u/lindig)\
**Post date:** [December 31, 2018, 11:30am UTC](https://discuss.ocaml.org/t/difference-between-files-beginning-with-upper-or-lower-case/3116/2 "2018-12-31T11:30:09Z")

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OCaml maps file names to modules:

- `abc.ml` becomes module `Abc`
- `Abc.ml` becomes module `Abc`
- `aBC.ml` becomes module `ABC`
- `ABC.ml` becomes module `ABC`

Capitalising the first letter in the file name has no effect since a module name is always capitalised. See [module\_of\_filename](https://github.com/ocaml/ocaml/blob/4.07/driver/compenv.ml#L85-L97) in the compiler source code.