ReasonML

We're going to explore type-driven development using ReasonML (https://reasonml.github.io/). Reason is a JavaScript-like syntax and is also a set of tools for OCaml (https://ocaml.org/). OCaml is a mature statically typed functional programming language with excellent support for object-oriented and modular programming.

We're going to write Reason code and compile it to JavaScript using the BuckleScript compiler (https://bucklescript.github.io/). BuckleScript takes input from Reason code and outputs essentially a simple subset of ES5 (that is, no ES2015-style classes, no arrow functions, and so on). This will allow us to write strongly statically typed code and see what the output JavaScript looks like with all the types stripped away.

The Reason toolkit currently consists of:

• A code formatting and syntax translation tool, refmt
• An interactive code evaluation environment, rtop
• A build manager for native-compilation projects (we won't need this one for this book), rebuild
• A tool that provides intellisense abilities to editors, ocamlmerlin-reason

These tools work together to provide a minimal, yet powerful, development experience. Together with a good editor (we recommend Visual Studio Code), they cover most of your day-to-day development needs.