This project file is needed in the root directory of every source tree that you want to compile with Dune. In general, you’ll have a dune file in every subdirectory of the source tree but only one dune-project file at the root.

let increment x = x + 1

There are five essential components to learning a language: syntax, semantics, idioms, libraries, and tools.

Parametric polymorphism: Functions and data structures can be parameterized over types. This is crucial for being able to re-use code.