ReasonML Quick Start Guide

Abstract types

Abstract types are type declarations that don't have a definition. Let's explore why this would be useful. In addition to bindings, module signatures can include types. In the following code, you'll notice that the module signature of Foo includes a person type, and now Foo must include this type declaration:

/* Foo.re */type person = {  firstName: string,  lastName: string};/* Foo.rei */type person = {  firstName: string,  lastName: string};

The person type is exposed in the same way as if there were no module signature defined. As you'd expect, if a signature is defined and the type is not listed, the type isn't exposed to other modules. There is also the option to leave the type abstract. We only keep what's left of the equals ...