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Chapter 1 Camlp4

Camlp4 is a Pre-Processor-Pretty-Printer for OCaml, parsing a source file and printing some result.

To run, Camlp4 needs to load files holding operations defining or modifying parsing (how to read the input file) and printing (how to print the result). Such files are OCaml object files (ending with ``.cmo'' or ``.cma'').

The command ``camlp4'' runs the Camlp4 program. The first options are objects (``.cmo'') or library (``.cma'') files which are loaded, selecting different parsing and printing operations. Among these first options, it is also possible to use the option ``-I'' to select directories where objects and library files are searched. But, important remark: by default, the system does not searches in the current directory: to select some object file, e.g. ``foo.cmo'' in the current directory, write ``./foo.cmo'' or add the option ``-I .''.

1.1 Camlp4 predefined files

The system provides some files, installed in Camlp4 library directory (depending on the installation, usually /usr/local/lib/camlp4: in the whole document, this directory is named camlp4-lib-dir). The provided files are:

• Parsing syntax:
  • pa_o.cmo: OCaml.
  • pa_r.cmo: Revised: this is an alternative syntax for the language (chapter 5).
• Printing syntax:
  • pr_o.cmo: Pretty print with OCaml syntax. Add an option -l to the command line to specify a line length.
  • pr_r.cmo: Pretty print with revised syntax. Add this option -l too.
  • pr_dump.cmo: Dump the syntax tree

Other predefined files allow to extend parsing and printing operations:

• Parsing extensions:
  • pa_oop.cmo: (to be loaded after ``pa_o.cmo'') Parsers and streams, with OCaml syntax, without code optimization, corresponding to what is internally generated by the OCaml compiler.
  • pa_op.cmo: (to be loaded after ``pa_o.cmo'') Parsers and streams, with OCaml syntax, with code optimization.
  • pa_rp.cmo: (to be loaded after ``pa_r.cmo'') Parsers and streams, with revised syntax and code optimization.
  • pa_extend.cmo: (to be loaded either after ``pa_o.cmo'' or ``pa_r.cmo'') Syntax extensions for the Camlp4 grammar system (Chapter 3).
  • pa_ifdef.cmo: add ifdef statement like in C (conditional compilation), in expressions or structure items. Add the options -D and -U to the camlp4 command line. To define the symbol FOO, either use ``