Camlp4 Deprecation Warning: this tutorial describes technology that is considered obsolete. It’s been replaced by extensions points and ppx rewriters. Camlp4 is part of the standard OCaml distribution and Camlp5 is distributed The title of the tutorial says Camlp4 but that is because it was written prior to the. Many of the tutorials below need updating and tutorials on many new topics are Camlp4 Tutorial (by Jake Donham), to build syntax extensions for OCaml with.
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Camlp4the OCaml “pre-processor pretty printer” is an advanced macro system which allows complex abstract syntax tree transformations on ocaml programs, and on other recursive decent grammars.
A (meta-)guide to CamlP4: Metaprogramming in OCaml · Andrei Formiga
To learn CamlP4, you must learn this alt syntax. The difference is only at the level of the concrete syntax, camllp4 these three versions are equivalent representations of the same abstract syntax tree. With quotations this is easier. Support for the original syntax inside quotations was added in OCaml 3. This can be used for defining parsers or extending existing ones. Many factors contribute to this.
Daniel de Rauglaudre wrote the original CamlP4, which was available for OCaml since its early versions. To extend the OCaml parser, it may be useful to take a look at how it is defined for the standard syntax es.
As demonstrated by the definition of a revised syntax for OCaml, the same programming language tutofial use different concrete syntaxes. Other target languages can also be used, such as C.
For example, this piece of code: The notion of concrete syntax refers to the format in which the abstract syntax is represented. From Wikipedia, the free encyclopedia. As this list shows, it is a very powerful and useful tool for parsing and metaprogramming.
Quotations allow the programmer to treat a piece of code as data instead of being part of the program itself. From the point of view of syntax extensions for OCaml, CamlP4 parses OCaml code, most likely using an extended syntax, generates an AST that may be filtered, and then prints it.
Memoization consists in storing the results of previous computations in a table so that the actual computation of the function for each possible argument occurs at most once. Domain-specific languages are a major application of Camlp4. To learn how to use quotations to generate OCaml AST nodes, you can look at this appendix from the same manual. Actually, although the old CamlP4 had an official reference manual and tutorial, the new CamlP4 has neither.
Most of them are linked in a previous part. The ocaml beta announcement: As I mentioned, this is not a tutorial on CamlP4. If you know the revised syntax, you can start to use quotations to generate OCaml code. Richard Jones posted an example in the official Caml-list for wrapping pattern matching in a predicate.
A proper tutorial would be quite useful, but it would also demand much more time from me, so I decided to do the next best thing: The latter one is defined as an extension of the former, so you may need to consult both.
Camlp4 stands for Caml Preprocessor and Pretty-Printer and one of its most important applications is the definition of domain-specific extensions of the syntax of OCaml. Grammars and Extensible Parsers CamlP4 makes it easy to create parsers, because it includes an embedded notation for parser generation.
You could feed the output of the pretty-printer to the OCaml compiler, thus effectively activating the syntax extension. This is similar to the way format strings work in printf-like functions.
Retrieved from ” https: CamlP4 is generally used to generate OCaml code, one way or another. This post is meant to be a guide to the available documentation and tutorials about CamlP4, assuming tutoriao previous experience with it.
tutoiral For example, this piece of code:. This page was last edited tjtorial 18 Novemberat OCaml syntax extensions Conceptually, the plan is simple: CamlP4 comes with parsers for the syntax of OCaml revised and original variants, possibly others. However, this has some disadvanges: He also uses quotations in original syntax in the earlier parts, rendering the example code unusable in current versions of OCaml in some cases he linked to newer versions that work.
It is often used to write syntax extensions to OCaml, like adding support for a notation for monads or for list comprehensions. So CamlP4 parses its input and then builds an abstract syntax tree out of it. Quotations and Abstract Syntax Quotations allow the programmer to cxmlp4 a piece of code as data instead of being part of the program itself.
The topics are presented in the best order IMO, of course for learning, under this assumption. Given textual input, CamlP4 parses the input into an abstract syntax tree, which is then printed in some format.
The abstract syntax yutorial is at the center of the syntax extensions, which are in fact OCaml programs.
So the first order of business if you want to learn to use CamlP4 is learning the Revised syntax. More examples can be found in the recommended sources below. The relevant files are pointed later, in the section about parsers. Between parsing and printing, it is possible to define AST Filters that can transform the tree, including maps and folds over it. Putting it all together: For now, there are no better options, so the only way out is to read both sources and try to integrate them mentally.
Back to the Revised syntax: