Quotations

 This chapter presents the Camlp4 quotation system. A quotation is a part of a program enclosed by special parentheses in position of expression or pattern, and whose treatment is done by an user function, called a ``quotation expander''. Several quotations expanders are usable in the same source code.

When Camlp4 encounters such a construction, the appropriate quotation expander is called with the string contents of the quotation.

There are two kinds of quotation expanders:

• Those returning strings. The returned string is parsed by Camlp4 afterwards. They are easy to use, but they depend on the language syntax: the returned string must be of Ocaml syntax if the language syntax used is Ocaml's, in Righteous syntax if the language syntax is the Righteous one, etc.
• Those returning syntax trees. They are independant from the language syntax used, but to use them, one muse know how to create syntax tree nodes. See appendix A.