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 It’s been replaced by extensions points and ppx rewriters.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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Camlp4 Wiki The ocaml beta announcement: Part 2 and part 3 tutoriial about quotations from the perspective of a user, while part 8 and part 9 are about implementing new quotations and antiquotations.
Given textual input, CamlP4 parses the input into an abstract syntax tree, which is then printed in some format. From Wikipedia, the free encyclopedia.
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. To learn CamlP4, you must learn this alt syntax. A Camlp4 preprocessor operates by loading a caklp4 of compiled modules which define a parser as well as a pretty-printer: This internal representation constitutes the abstract syntax tree AST.
And now for the punchline: Quotations allow the programmer to treat a piece of code as data instead of being part of the program itself. Views Read Edit View history. CamlP4 is mostly used as a metaprogramming tool tutoria OCaml, but it can be used in many ways: 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: CamlP4 comes with parsers for the syntax of OCaml revised and original variants, possibly others.
It is also possible to have a quotation inside an antiquotation, and an antiquotation inside this quotation that is inside the antiquotation of the original quotation, and so on. The latter one is defined as an extension uttorial the former, so you may need to consult both. Quotations and Abstract Syntax Quotations allow the programmer to treat a piece of code as data instead of being part of the program itself.
Before attempting to learn CamlP4, it is recommended to learn how to program in OCaml reasonably well, and to have at least some familiarity with parsing and programming language tools. This AST will be emitted, or printed, in a chosen format. So tutoriwl fork ensued: The following example defines a syntax extension of OCaml. The relevant files are pointed later, in the section about parsers.
With quotations this is easier. To extend the OCaml parser, it may be useful to take a camllp4 at how it is defined for the standard syntax es.
OCaml Tutorials – OCaml
Although the definition of grammars must be done in OCaml, the parser that is being defined or extended is not necessarily related to OCaml, in which case the syntax tree that is being manipulated is not the one of OCaml. If you know the revised syntax, you can start to use quotations to generate OCaml code. CamlP4 is generally used to generate OCaml code, one way or another. Expanders can also generate strings instead of AST nodes, although this is less useful.
If the target language is OCaml, simple syntax add-ons or syntactic sugar can be defined, in order to provide an expressivity which is not easy to achieve using the standard features of the OCaml language. Back to the Revised syntax: It is also tuutorial to define new printers, though most of the time this is not very useful. I hope this post helps people get up to speed in using this handy tool. Many factors contribute to this. De Rauglaudre maintains a separate backward-compatible version, which has been renamed Camlp5.
However, this has some disadvanges:. The intention is to give the Tutorixl Picture, so that the details can be worked out later.
Any loaded module can extend a grammar defined in another module, and an extension can not only add new productions, but also change existing ones or even delete them. Richard Jones posted an example in the official Caml-list for wrapping pattern matching in a predicate.
The series of posts on CamlP4 over at Ambassador at the Computers is a good source, with some caveats. The ocaml beta announcement: The new CamlP4 wiki has useful stuff, although it is incomplete both as a tutorial and as a reference.
Camlp4 – Wikipedia
Domain-specific languages are a major application of Camlp4. Besides the above-linked tutorials in the CamlP4 wiki, the section about grammars in the old manual is still very useful. In the beta announcement, there was mention of new binaries camlp4xxx that come preloaded with selections of tutotial and old syntaxes.
Putting it all together: