META(5) File Formats Manual META(5)
NAME
META - [File that specifies metainformation of OCaml packages]
GRAMMAR
metafile ::= entry*
entry ::= assignment | addition | subpackage
subpackage ::= "package" pkgname '(' metafile ')'
assignment ::= variable_name [ formal_predicates ] '=' value
addition ::= variable_name [ formal_predicates ] '+=' value
formal_predicates ::= '(' formal_predicate { ',' formal_predicate } ')'
variable_name ::= name
formal_predicate ::= name | '-' name
name ::= [ 'A'-'Z' 'a'-'z' '0'-'9' '_' '.' ]+
pkgname ::= '"' (character but not '.')* '"'
value ::= '"' character* '"'
DESCRIPTION
If a package directory contains a file with the fixed name "META" it is
interpreted as described here. The file is a sequence of entries fol-
lowing the given grammar; every entry defines a variable under a cer-
tain condition given by the list of formal predicates, or it introduces
a subpackage.
There is a list of predefined variables and a list of standard predi-
cates. These variables define: required packages, description, version
information, directories, archive files, and linker options. The predi-
cates denote circumstances of the application of the variables: whether
the bytecode or the native compiler is used, if there is a toploop com-
piled in, details of multi-threading execution, details of profiling.
DETAILS OF THE FILE FORMAT
The file consists of a sequence of entries which must be formed as the
grammar prescribes. The lexical tokens are names, values, and inter-
punctuation like '(', ',' and so on. Note that linefeeds do not play a
special role, i.e. an entry definition may be given in more than one
line, or several definitions may occur on a single line. There may be
comments which begin with '#' and run until the end of the line.
Names are sequences of the characters A-Z, a-z, 0-9, or _. Names con-
taining capital letters and names beginning with digits are allowed but
not recommended.
Values are enclosed between double quotes. Values may contain any char-
acter. The characters " and \ must be preceded by backslashes.
Package names must not contain the '.' character because it is used as
delimiter of compound names.
MAIN PACKAGES AND SUBPACKAGES
The outermost variable assignments and additions belong to the main
package. The name of the main package is not defined within META; it is
either the name of the directory containing META or the suffix of the
META file (if the name of the META file is formed like META.name).
The keyword package starts the definition of a subpackage. There must
not be two such definitions with the same name. Within the parantheses,
the variable assignments and additions refer to the subpackage. It is
allowed that a subpackage contains further subpackages.
The package name following package is the local name relative to the
main package, i.e. the name of the main package is not mentioned. At
all other places, however, the subpackage must be prefixed by the name
of the containing package, separated by a '.'.
Subpackages are independent of the containing package, except that the
subpackage points to the same installation directory as the containing
package (i.e. the location of the installation directory is inherited
from the containing package).
SEMANTICS OF VARIABLE DEFINITIONS
In order to determine the value of a variable, first all assignments
are inspected, and the most specific assignment is taken (if there is
none, the empty string will be taken as value). In a second step, all
additions are gone through one after the other in the order they occur
in the file, and the values of all matching additions are appended to
the current value. In the following, it is further clarified which as-
signment is the most specific, which additions actually match, and how
the details of the value addition look like.
The most specific assignment is selected upon a set of actual predi-
cates, i.e. the set of predicates that are assumed to be true. The
predicates occuring in the definitions of assignments and additions are
called formal predicates. They may be positive or negative; the latter
are prepended by a '-' sign. In order to determine the value after the
evaluation of the assignments, the following rules apply:
• An assignment can only be used if all positive formal predicates
are included in the set of actual predicates, and if all nega-
tive formal predicates are not included in the set of actual
predicates. Such an assignment is called applicable. If there is
no such assignment, the variable will have no value.
• If there is more than one applicable assignment, the definition
with the biggest number of formal predicates is selected.
• If there is still more than one applicable assignment, both ap-
plicable and with a maximum number of formal predicates, the
definition that is defined first is selected.
An addition is matching when all positive formal predicates are in-
cluded in the set of actual predicates, and all negative formal predi-
cates are not included.
The value of an addition is appended to the current value with implicit
white space as separator.
VARIABLES
There is a set of variables with predefined meaning:
• The variable "directory" redefines the location of the package
directory. Normally, the META file is the first file read in the
package directory, and before any other file is read, the "di-
rectory" variable is evaluated in order to see if the package
directory must be changed. The value of the "directory" variable
is determined with an empty set of actual predicates. The value
must be either: an absolute path name of the alternate direc-
tory, or a path name relative to the stdlib directory of OCaml
(written "+path"), or a normal relative path name (without spe-
cial syntax). In the latter case, the interpretation depends on
whether it is contained in a main or sub package, and whether
the standard repository layout or the alternate layout is in ef-
fect (see site-lib for these terms). For a main package in stan-
dard layout the base directory is the directory physically con-
taining the META file, and the relative path is interpreted for
this base directory. For a main package in alternate layout the
base directory is the directory physically containing the
META.pkg files. The base directory for subpackages is the pack-
age directory of the containing package. (In the case that a
subpackage definition does not have a "directory" setting, the
subpackage simply inherits the package directory of the contain-
ing package. By writing a "directory" directive one can change
this location again.)
• The variable "requires" specifies the list of required packages.
The names of the packages must be separated by white space
and/or commas. The names must be fully qualified (i.e. when they
refer to a subpackage, the names of all containing packages must
be prepended, separated by '.').
• The variable "description" may include a short description of
the package (displayed by ocamlfind list).
• The variable "version" specifies the version string.
• The variable "archive" specifies the list of archive files.
These files should be given either as (1) plain names without
any directory information; they are only searched in the package
directory. (2) Or they have the form "+path" in which case the
files are looked up relative to the standard library. (3) Or
they have the form "@name/file" in which case the files are
looked up in the package directory of another package. (4) Or
they are given as absolute paths.
The names of the files must be separated by white space and/or
commas. In the preprocessor stage, the archive files are passed
as extensions to the preprocessor (camlp4) call. In the linker
stage (-linkpkg), the archive files are linked. In the compiler
stage, the archive files are ignored.
Note that "archive" should only be used for archive files that
are intended to be included in executables or loaded into
toploops. For modules loaded at runtime there is the separate
variable "plugin".
• The variable "plugin" specifies the plugin archives of the pack-
age. These can be dynamically loaded with the Fl_dynload module.
The plugin archives can have ".cmo", ".cma", or ".cmxs" suffix.
• The variable "linkopts" specifies additional linker options.
• The variable "error" can be used to signal error conditions.
When this variable is applicable, the ocaml compilers are
stopped, and an error message is printed. The message is the
value of the variable.
• The variable "warning" can be used to signal warnings. When this
variable is applicable, the warning is printed, but the compila-
tion continues. The message is the value of the variable.
• The variable "exists_if" can be used to disable subpackages. The
value of "exists_if" is a file; the subpackage is hidden if this
file does not exist. You can also enumerate several files, and
the subpackage is hidden if none of the files exist.
• The variable "ppx" is a command that is added to the compiler
invocation via the -ppx option (available since OCaml-4.01). If
the command is relative to the current directory (e.g. ./cmd),
the command is expected in the package directory. The special
forms as defined for "archive" are also available (e.g. @oth-
erpkg/cmd). Additional arguments can be specified on the
ocamlfind command line with the -ppxopt option or the "ppxopt"
variable.
• The variable "ppxopt" is a set of options that are added to the
ppx rewriter invocation. The contents of the variable consists
of one or several whitespace-separated parts. Every part con-
sists of several comma-separated subparts; the first subpart in-
dicates the package that contains the ppx rewriter invocation,
the rest contain the options to be appended. If the option is a
path relative to the current directory (e.g. ./foo.cma), the
path is expanded relative to the package directory. The special
forms as defined for "archive" are also available (e.g. @oth-
erpkg/foo.cma).
It is possible to define additional variables but there is currently no
software interpreting them.
PREDICATES
There is a list of standard predicates:
• The "byte" predicate means that the bytecode compiler is used.
• The "native" predicate means that the native compiler is used.
• The "toploop" predicate means that the toploop is available in
the linked program. It is only set when the toploop is running,
not when the toploop is generated.
• The "create_toploop" predicate means that a toploop is created
(using ocamlmktop).
• The "mt" predicate means that the program is multi-threaded.
• The "mt_posix" predicate means that in the case "mt" is set,
too, the POSIX libraries are used to implement threads.
• The "mt_vm" predicate means that in the case "mt" is set, too,
the VM-based libraries are used to implement threads.
• The "gprof" predicate means that in the case "native" is set,
too, the program is compiled for profiling
• The "autolink" predicate means that ocamlc can/will perform au-
tomatic linking.
• The "preprocessor" predicate means that the META variables are
scanned for preprocessor options.
• The "syntax" predicate means that the -syntax option is present
on the command line.
• Legacy: The "plugin" predicate could be used in some versions of
findlib to select cmxs archives instead of cmxa archives. This
use is still possible but discouraged.
In addition to these predicates, there are package predicates for every
package that is finally selected. Of course, this kind of predicate
must not be used to select "directory" and "requires" variables, but
for the other variables they are perfectly valid. The package predi-
cates have the form "pkg_" plus the name of the package (fully quali-
fied).
User Manual The findlib package manager for OCaml META(5)
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