ReasonML Quick Start Guide

Module types

A module signature can also be defined using the module type keyword instead of using a separate .rei file. The module type must start with a capital letter. Once defined, a module can be constrained by a module type using the module <Name> : <Type> syntax, as follows:

module type FooT {  let foo: (~a: int, ~b: int) => int;};module Foo: FooT {  let foo = (~a, ~b) => a + b;};

The same module type can be used for multiple modules, as follows:

module Bar: FooT {  let bar = (~a, ~b) => a - b;};

We can think of module signatures as interfaces in the object-oriented sense. The interface defines the properties and methods that a module must define. In Reason, however, module signatures also hide bindings and types. But perhaps one of the ...