modules.md

Modules

Guide-level Explanation

Each source file is a module.

Each file starts with a module header. Currently ProjectName is same as directory name and ModuleName is same as file name (excluding extension). (See also Projects.)

module rec ProjectName.ModuleName

Symbols defined in a module are separated from other modules. To access symbols in other modules, there are several ways: module synonyms and open statements.

Module Synonyms

A module statement defines a module synonym.

module A = P.M

A is module synonym that denotes to other module P.M.

For example:

// P/A.milone
module P.A

let f () = ()

// P/B.milone
module P.B

module A = P.A

// Now you can use `f` defined in `A`.
let g () = A.f ()

Open Declarations

After open statement, all symbols defined in specified module are visible in the current module.

// P/A.milone
module P.A

let f () = ()

// P/B.milone
module P.B

open P.A

let g () = f () // f is defined in `P.A`

Private Symbols

private keyword in front of defined symbol hides it from other modules.

module P.A

// These types and functions can't be referenced from other modules.
type private InnerTy = | InnerTy of int
let private innerFun () = ()

Advanced Topics

• module rec is implemented, but non-recursive module isn't.

Comparison with F#

In F#, each project has a project file (.fsproj). It describes:

• the ordered list of modules in the project
• and other projects that the project refers to.