MetaOCaml

MetaOCaml is an extension of the OCaml programming language that enables multi-stage programming, allowing programs to generate and manipulate code as data. It introduces the notion of first-class code values, so a piece of code can be treated as a value that can be produced, transformed, and then executed.

At the core of MetaOCaml is a staging mechanism. Programmers write code that produces code for a future stage, creating specialized or optimized versions of programs. The language provides quotation and anti-quotation constructs to build code fragments and to splice host-language values into generated code. A primitive or construct is available to run the generated code, yielding a result in the original program’s execution.

The type system in MetaOCaml ensures that generated code is well-typed, enabling safer metaprogramming. By keeping code generation within the type discipline of OCaml, it aims to prevent the generation of ill-typed code and to provide compile-time guarantees about staged programs.

Common use cases include embedding domain-specific languages via code generation, program specialization and partial evaluation, and the creation of compilers, preprocessors, or performance-oriented libraries that generate specialized code paths. MetaOCaml can reduce boilerplate and enable efficient abstractions by pushing work into code generation rather than at runtime.

As a research-oriented extension, MetaOCaml has influenced subsequent work on typed code generation and macro systems in ML-family languages. It sits alongside OCaml as a former milestone in the exploration of expressive, type-safe metaprogramming techniques.