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 It’s been replaced by extensions points and ppx rewriters.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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The intention is to give the Big Picture, so that the details can be worked out later. Back to the Revised syntax: So the first order of business if you want to learn to use CamlP4 is learning the Revised syntax.
Camlp4 is a software system for writing extensible parsers for programming languages. 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. Besides the above-linked tutorials in the CamlP4 wiki, the section about grammars in the old manual is still very useful.
Its original author is Daniel de Rauglaudre. To extend the OCaml parser, it may be useful to take a look at how tutoriql is defined for the standard syntax es.
Richard Jones posted an example in the official Caml-list for wrapping pattern matching in a predicate. It can be output in a binary form, e. Several libraries are provided which facilitate the specific manipulation of OCaml syntax trees.
For example, this piece of code: This is similar to the way format strings work in printf-like functions. The topics are presented in the best order IMO, of course for learning, under this assumption.
The reason for the title will be explained in a bit. However, this has some disadvanges: It’s been replaced by extensions points and ppx rewriters Camlp4the OCaml “pre-processor pretty printer” is an advanced macro system which allows complex abstract syntax tree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.
The sequence could start better. As demonstrated by the definition of a revised syntax for OCaml, the same programming language can use different concrete syntaxes. The ocaml beta announcement: Camlp4 Wiki The ocaml beta announcement: Besides that, there are always the sources. This post is meant to be a guide to the available documentation and tutorials about CamlP4, assuming no previous experience with it.
CamlP4 uses an alternative concrete syntax for OCaml.
Ambassador to the Computers: Reading Camlp4
They would all converge to an abstract syntax tree in a unique format that a compiler can handle. It is also possible to define new printers, though most of the time this camlp44 not very useful. To learn how to use quotations to generate OCaml AST nodes, you can look at this appendix from the same manual. Views Read Edit View history.
Given textual input, CamlP4 parses the input into an abstract syntax tree, which is then printed in some format. Other target languages can also be used, such as C. Grammars and Extensible Parsers: Instead, each template has gaps that must be filled with data which depends on the situation.
Camlp4 underwent a major revision between the version included in ocaml 3. CamlP4 is generally used to generate OCaml code, one way or another.
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. 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. To use this from the OCaml compilers, you just need to use the -pp command-line flag. So as an example: Since OCaml is a multi-paradigm language, with an interactive toplevel and a native code tutorizl, it can be used as a backend for any kind of original language.
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. 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: 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.
The marshaled tree also includes location information, which allows the compiler to report errors correctly for the input source. Support for the original syntax inside quotations was added in OCaml 3. The following example defines a syntax extension of OCaml.