META -- [File that specifies metainformation of OCaml packages]


         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* '"'


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 following the given grammar; every entry defines a variable under a certain 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 predicates. These variables define: required packages, description, version information, directories, archive files, and linker options. The predicates denote circumstances of the application of the variables: whether the bytecode or the native compiler is used, if there is a toploop compiled in, details of multi-threading execution, details of profiling.


The file consists of a sequence of entries which must be formed as the grammar prescribes. The lexical tokens are names, values, and interpunctuation 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 containing capital letters and names beginning with digits are allowed but not recommended.

Values are enclosed between double quotes. Values may contain any character. The characters " and \ must be preceded by backslashes.

Package names must not contain the '.' character because it is used as delimiter of compound names.


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

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).


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 assignment 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 predicates, 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 addition is matching when all positive formal predicates are included in the set of actual predicates, and all negative formal predicates are not included.

The value of an addition is appended to the current value with implicit white space as separator.


There is a set of variables with predefined meaning:

It is possible to define additional variables but there is currently no software interpreting them.


There is a list of standard predicates:

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 predicates have the form "pkg_" plus the name of the package (fully qualified).