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 It’s been replaced by extensions points and ppx rewriters.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 uses an alternative concrete syntax for OCaml. CamlP4 comes with parsers for the syntax of OCaml revised and original variants, possibly others. They would all converge to an abstract syntax tree in a unique format that a compiler can handle. So a fork ensued: So as an example: A good idea is to look at examples of simple syntax extensions.
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.
As this list shows, it is a very powerful and useful tool for parsing and metaprogramming.
The difference is only at the level of the concrete syntax, since these three versions are equivalent representations of the same abstract syntax tree. A Camlp4 preprocessor operates by loading a collection of compiled modules which define a parser as well as a pretty-printer: The relevant files are pointed later, in the section about parsers.
Other target languages can also be used, such as C. OCaml syntax extensions Conceptually, the plan is simple: Views Read Edit View history. The good thing about grammars and parsers in CamlP4 is that they are extensible. However, this tutorual some disadvanges:. Instead, each template has gaps that must be filled with data which depends on the situation. The generated AST can be emitted by a pretty-printer, showing code in a readable format for humans.
The ocaml beta announcement: CamlP4 is mostly used as a metaprogramming tool for OCaml, but it can be used in many ways: This is similar to the way format strings work in printf-like functions. To extend the OCaml parser, it may be useful to take a look at how it is defined for the standard syntax es.
However, this type is recursive as expected for an AST and trees for any non-trivial piece of code will be complicated to create as a value of the AST camlpp4. The output of the program is as follows, showing that the fac function factorial only computes products that were not computed previously:. Between parsing and printing, it is possible to define AST Filters that can transform the tree, including maps and folds over it.
OCaml Tutorials – OCaml
The marshaled tree also includes location information, which allows the compiler to report errors correctly for the input source.
Camlp4 underwent a major revision between the version included in ocaml 3. Or read the CamlP4 sources, in this case the OCaml parsers. Warning this page contains advanced material. CamlP4 is generally used to generate OCaml code, one way or another. Sources and Final Thoughts CamlP4 gives OCaml programmers much of the power of metaprogramming available in Lisp languages, added with static type checking and customizable components.
They are widely used in Lisp because of its uniform representation for code and data, and are widely used when programming in CamlP4 because they make it easier to generate code. The intention is to give the Big Picture, so that the details can be worked out later. It’s been replaced by extensions points and ppx rewriters.
Camlp4 Wiki The ocaml beta announcement: The reason for the title will be explained in a bit. I know this sounds confusing, as messing with quotations can often be, but in most cases it is easier to learn them by example. For now, there are no better options, so the only way out is to read both sources and try to integrate them mentally.
Grammars and Extensible Parsers CamlP4 makes it easy to create parsers, because it includes an embedded notation for parser generation. 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.
With quotations this is easier. This can be used for defining parsers or extending existing ones. The only thing that the developer has to do is write a Camlp4 grammar which converts the domain-specific language in question into a tutoral OCaml program. However, there is a good source of examples of the revised syntax: To learn CamlP4, you must learn this alt syntax. Part 2 and part 3 are about quotations from the perspective of a user, while part 8 and part 9 are about implementing new quotations and camp4.
CamlP4 itself is written in this syntax.