Camlp4 and Template Haskell
Friday, October 01, 2010 - 02:00 PM - 06:00 PM
"Static metaprogramming" is compile-time code analysis and synthesis. It has many applications, such as (from simple to complex): defining abbreviations, generating boilerplate from type definitions, extending the language syntax, and embedding DSLs.
Static metaprogramming is supported for Haskell with Template Haskell, and for OCaml with Camlp4; the two systems have a lot in common. In this tutorial we will work through examples in both languages, sticking mostly to their commonalities. We will also say a little about features which are unique to each.
The main features we will cover are:
- host language syntax trees
- quotations / antiquotations for host language syntax trees
- defining new quotations
- pragmatics of each tool
(Quotations / antiquotations are a mechanism for working with host language abstract syntax trees using the concrete syntax of the host language.)
We will motivate these features through examples of increasing complexity, including a simple DSL for working with JSON data.
Participants will leave with a basic understanding of how to build syntax extensions with the two systems, including how to run the tool, how to work with the host language syntax trees using quotations and antiquotations, and how to define new quotations to extend the host language.
Participants should be familiar with either OCaml or Haskell, but we will assume no prior knowledge of Template Haskell or Camlp4. It would be helpful to know the basics of parsing (lexing vs. parsing, abstract syntax trees, recursive descent) and be familiar with at least one parser generator.
Participants should have recent versions of Objective Caml and the Haskell Platform installed. Objective Caml is available here:
The Haskell platform is available here:
For OCaml, participants need to install Findlib:
and for both OCaml and Haskell the tutorial materials are at:
is the author of several OCaml free software projects, and blogs about OCaml at Ambassador to the Computers. Jake previously spoke about the ocamljs project at CUFP 2008.
When learning programming in the engineering school of EPITA in Paris, Nicolas Pouillard first met meta-programming using Camlp4 for very basic syntax extensions, C++ templates and program transformation using Stratego/XT. Then he entered the research team of Xavier Leroy at INRIA. He first spent six months as an intern for the renovation of Camlp4 under the direction of Michel Mauny. He continued with him by accepting an engineer job on a project joint with Intel. During this contract he worked on a new front-end (written in OCaml) for their in-house functional language featuring overloading and meta-programming facilities. During these months he also learned Haskell and in particular meta-programming through Template Haskell. Finally he continued as a PhD on "Safer and more expressive languages for meta-programming" directed by Francois Pottier. In this work we aim at leveraging safety features like strong typing and lexical scoping to manipulated programs within a meta-programming language.