Camlp5 sources

Information for developpers of the Camlp5 program.

  1. Kernel
  2. Compatibility
  3. Tree structure
  4. Fast compilation from scratch
  5. Testing changes
  6. Before committing your changes
  7. If you change the main parser
  8. Adding new nodes to the syntax tree
  9. Switching between transitional and strict mode
  10. Bootstrapping


The sources are composed of:

Some other directories contain configuration files, tools, documentation and manual pages.

The kernel is sufficient to make the core system work: it is possible to compile and bootstrap only it. All sources being in revised syntax, the first compilation of Camlp5 is done by a version of this kernel in pure OCaml syntax, located in the directory ocaml_src.

These sources in pure OCaml syntax are not modified by hand. When changes are made to the kernel, and a check is done that it correctly compiles and bootstraps, the kernel in pure OCaml syntax is rebuilt using Camlp5 pretty print. This is done by the command "make bootstrap_sources".


This distribution of Camlp5 is compatible with several versions of OCaml. The definition of OCaml syntax trees may change from OCaml version to version, which can be a problem. Since OCaml does not install the sources nor the compiled versions of its syntax tree, a copy of the necessary source files, borrowed from the source of the OCaml compiler is in the directory 'ocaml_stuff', in subdirectories with the OCaml version number.

If the present distribution of Camlp5 is not compatible with the version of OCaml you have (the command 'configure' tells you), it is possible to add it. For that, you need the sources to your specific OCaml distribution. If you have them then a 'configure' telling you that camlp5 is not compatible, do:

  make steal OCAML_SRC=<path-to-OCaml-sources>

This creates a new directory in 'ocaml_stuff' with sources of the syntax tree of your OCaml compiler.

If you want to check that the sources of the syntax tree of OCaml are up-to-date (e.g. if this is the current OCaml developpement), do:

  make compare_stolen OCAML_SRC=<path-to-OCaml-sources>

The compatibility is also done with the file 'lib/', which is a module containing miscellaneous features depending to the version of OCaml.

In the directory 'ocaml_src' which contains the pure OCaml sources of the Camlp5 core (see chapter TREE STRUCTURE below), there are as many versions of this files as versions of OCaml. They are named '' in the directory 'lib/versdep'. If you are adding a new version of OCaml, you need this file. As a first step, make a copy from a close version:

  cd ocaml_src/lib/versdep
  cp <close_version>.ml <version>.ml

Then, you can rerun "configure" and do "make core". If the file 'ocaml_src/lib/' has compilation problems, fix them 'make core' again. When it compiles, copy it into the subdirectory 'versdep' as '<version>.ml', overwriting the version you copied from the close version.

Later, the same file 'lib/' in Camlp5 syntax may have similar compilation problems. There is only a single version of this file, thanks to IFDEF constructs used here or there.

While compiling with some specific version of OCaml, this file is compiled with 'OCAML_vers' defined where 'vers' is the version number form the beginning to the first space or charcter '+' with all dots converted into underscores. For example, if your OCaml version is 7.04.2+dev35, you can see in the compilation process of that OCAML_7_04_2 is defined, and you can add statements defined by the syntax extension 'pa_macro.cmo', for example IFDEF OCAML_7_04_2. Add statements like that in 'lib/' to make it compile successfully.

Tree structure

The directory 'ocaml_src' contains images in pure OCaml syntax of the directories odyl lib main and meta. This allows the creation of a core version of Camlp5 with only the OCaml compiler installed.

You can decompose the building of the Camlp5 core into:

1. make library_cold
just makes the directory 'ocaml_src/lib' and copy the cmo and cmi files into the directory 'boot'
2. make compile_cold
makes the other directories of ocaml_src
3. make promote_cold
copies the executables "camlp5", "camlp5r" and the syntax extensions (cmo files) into the directory 'boot'

From this point, the core Camlp5 is in directory 'boot'. The real sources in the top directories odyl, lib, main and meta, which are written in revised syntax with some syntax extensions (grammars, quotations) can be compiled. To achieve their compilation, you can do:

  make core

Or to compile everything do:

  make all

or just:


Notice that doing "make core" or "make all" from scratch (after a make clean), automatically starts by making the core files from their pure OCaml versions.

Fast compilation from scratch

  make clean core compare
  make coreboot
  make all opt opt.opt

Testing changes

1. do your changes

2. do:

  make core compare

if it says that the bootstrap is ok, you can do:

  make all
  make opt
  make opt.opt

otherwise, to make sure everything is ok, first do:

  make coreboot

sometimes two bootstraps ('make coreboot' twice) are necessary, in particular if you change things in the directory 'lib'. It is even possible that three bootstraps are necessary.

If things go wrong, it is possible to return to the previous version by typing:

  make restore clean_hot

then you can change what is necessary and continue by typing:

  make core

and test the bootstrap again:

  make coreboot

After several bootstraps (by 'make coreboot' or 'make bootstrap'), many versions are pushed in the directory 'boot' (you can type 'find boot -type d -print' to see that). If your system correctly bootstraps, you can clean that by typing:

  make cleanboot

which keeps only two versions. (The command 'make clean' also removes these stack of versions.)

Before committing your changes

Make sure that the cold start with pure OCaml sources work. For that, do:

  make compare_sources | less

This shows you the changes that would be done in the OCaml pure sources of the directory ocaml_src.

To make the new versions, do:

  make new_sources
  make promote_sources

Notice that these pure OCaml sources are not supposed to be modified by hand, but only created by the above commands. Although their source is pretty printed they are usually not easy to read, particularly for expanded grammars (of the statement 'EXTEND').

If these sources do not compile, due to changes in the OCaml compiler, it is possible however to edit them. In this case, similar changes may need to be performed in the normal sources in revised syntax.

After doing 'make new_sources' above, and before doing 'make promote_sources' below, it is possible to do 'make untouch_sources' which changes the dates of the newly created files with the dates of the old files if they are not modified. This way, the "svn commit" will not need to compare these files, which may be important if your network is not fast.

The 'make new_sources' builds a directory named ''. If this directory still exists, due to a previous 'make new_sources', the command fails. In this case, just delete it (rm -rf without problem: this directory is not part of the distribution, it is just temporary.

The 'make clean_sources' deletes old versions of ocaml_src, keeping only the last and the before last ones.

The command:

  make bootstrap_sources

is a shortcut for:

  make new_sources
  make untouch_sources
  make promote_sources
  make clean_sources

If there are changes in the specific file 'lib/', do also:

  make compare_all_versdep

and possibly:

  make bootstrap_all_versdep

because this file, in 'ocaml_src/lib/versdep' directory has different versions according to the OCaml version.

After having rebuilt the pure OCaml sources, check that they work by rebuilding everything from scratch, starting with "configure".

If you change the main parser

If you change the main parser 'meta/', you should check that the quotations expanders of syntax tree 'meta/' match the new version. For that, do:

  cd meta
  make compare_q_MLast

If no differences are displayed, it means that '' is ok, relatively to ''.

Otherwise, if the displayed differences seem reasonable, update the version by typing:

  make bootstrap_q_MLast

Then returning to the top directory, do 'make core compare' and possibly 'make coreboot' (one of several times) to check the correctness of the file.

And don't forget, if you want to commit, to re-create the pure OCaml sources like indicated above.

Adding new nodes to the syntax tree

If new nodes are necessary in the syntax tree, for example because the OCaml language added itself new nodes, the steps are the following (with the example of adding the "lazy" pattern node).

Switching between transitional and strict mode

If Camlp5 is compiled in some mode, it is possible to change its mode in two boostrapping steps. Type:

  make MODE=T coreboot

to switch to transitional mode, or:

  make MODE=S coreboot

to switch to strict mode.

After two (necessary) bootstraps, the kernel is compiled in the new mode. Complete the compilation by:

  make MODE=T all opt opt.opt


  make MODE=S all opt opt.opt

according to the new mode you want to use.

Another solution is, of course, recompile everything from scratch:

  make clean
  ./configure -transitional
  make world.opt


  make clean
  ./configure -strict
  make world.opt


Camlp5 is bootstrapped in numerous ways.

Camlp5 executable bootstrapping

The file 'main/camlp5r' is rebuilt each time a bootstrapping command is used (like 'make coreboot' or 'make bootstrap'). This bootstrapping command starts with copying it in the directory 'boot'. The file 'boot/camlp5r' is used to recompile the sources, creating another file 'main/camlp5r'. When both files are the same (byte by byte), the Camlp5 executable is bootstrapped.

Sometimes, in particular when changes are done in the library (directory 'lib'), it is necessary to bootstrap twice before having the message 'Fixpoint reached, bootstrap succeeded'.

The command 'make compare' tells you whether the Camlp5 executable is currently bootstrapped or not.

Source bootstrapping

The compilation of Camlp5 starts with the compilation of files of the directory ocaml_src written in pure OCaml. This creates the files 'camlp5' and 'camlp5r' in the directory boot. This is called the 'cold start'.

Once done, the sources of Camlp5 can be compiled using revised syntax and several syntax extensions, like the statement 'EXTEND', for example, and the quotations of syntax trees.

The core files of Camlp5 are in the directories lib, main, meta, odyl. There are the same directories in the directory ocaml_src where all files are equivalent.

When changes are done in the core files, and when the printer kit in normal syntax 'etc/pr_o.cmo' has been created, the files of the directory ocaml_src can be rebuilt using the command 'make bootstrap_sources'. This updates the files in ocaml_src to exactly reflect the ones in the core, but in pure OCaml syntax.

Bootstrap: the1 files in ocaml_src creates the first Camlp5 executable. The Camlp5 executable can rebuild the files in ocaml_src.

Source file bootstrapping

The source file meta/ (quotation of syntax trees) can be recreated using the file meta/ (revised syntax). When changes are done in the file meta/, a good usage is to go to the directory 'meta' and type:

    make compare_q_MLast

This shows the possible changes that will be applied to meta/ If they seem to be reasonable, do:

    make bootstrap_q_MLast

This changes the source file meta/ After this command, a new 'make compare_q_MLast' indicates no differences.

After that, a new 'make bootstrap' in the top directory ensures that everythings works.

Bootstrap: the file meta/ uses the quotation expander meta/q_MLast.cmo. The source file meta/ is recreated by meta/

Source file bootstrapping

The source file meta/ contains another version of the quotation expander of syntax trees which follows the current syntax used (in normal syntax if the current syntax is used). This works only in strict mode.

This file depends on the definition of the syntax tree main/mLast.mli. When changes are done in this file, it is possible to see what changes are impacted in meta/ For this, go to the directory 'meta' and type:

    make compare_q_ast

This shows the possible changes that will be applied to meta/ If they seem to be reasonable, do:

    make bootstrap_q_ast

This changes the source file meta/ After this command, a new 'make compare_q_ast' indicates no differences.

After that, a new 'make bootstrap' in the top directory ensures that everythings works.

Lisp and Scheme syntax bootstrapping

The Lisp syntax is written in Lisp syntax in the directory etc. It is the file 'etc/'. To compile this file, there is another file, named 'etc/' written in revised syntax.

When changes are done in etc/, the file etc/ must be rebuilt. First, go to the directory 'etc' and type:

    make compare_lisp

If changes seem to be reasonable, do:

    make boostrap_lisp

This rebuilds 'etc/'. A new 'make' in the directory 'etc' will recompile it and recompile the Lisp version 'etc/'.

Bootstrap: etc/ allows to compile etc/, and changes is etc/ are reported in the source file etc/ through 'make bootstrap_lisp'.

Same for the Scheme syntax: the files are etc/ and 'etc/'.

EXTEND statement bootstrapping

The EXTEND statement of Camlp5 is a syntax extension. The file 'meta/' contains the statement for the adding of this syntax extension, therefore something like:

        [ [ "EXTEND" .....

To be compiled, the file 'meta/' needs 'pa_extend.cmo'. This is actually its previous version in the directory 'boot'. When checking for a correct bootstrapping of Camlp5 (with the command 'make compare', for example), a test is done to verify that the binary files 'meta/pa_extend.cmo' and 'boot/pa_extend.cmo' are the same.

Notice that there is also a file 'ocaml_src/meta/' in pure OCaml syntax, but, although this file is pretty printed, is is hardly editable, because the expansion of the 'EXTEND' statement is a very long expression rather difficult to understand. But this file need not to be changes, since the command 'make bootstrap_sources' (see above) rebuilts it.

Copyright 2007-2012 Daniel de Rauglaudre (INRIA)

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