entry ::= variable_name [ formal_predicates ] '=' value
formal_predicates ::= '(' formal_predicate { ',' formal_predicate } ')'
variable_name ::= name
formal_predicate ::= name
name ::= [ 'A'-'Z' 'a'-'z' '0'-'9' '_' ]+
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.
There is a list of predefined variables and a list of standard predicates. These variables define: required packages, 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 consist of the rest 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.
There may be multiple definitions for the same variable if the lists of formal predicates are different. The effective definition is selected upon a set of actual predicates, i.e. the set of predicates that are assumed to be true. In order to determine the value of a variable, the following rule applies:
A definition can only be used if all formal parameters are included in the set of actual parameters, such a definition is called applicable. If there is no such definition, the variable has no value.
If there is more than one applicable definition, the definition with the biggest number of formal parameters is selected.
If there is still more than one definition, both applicable and with a maximum number of formal parameters, the definition that is defined first is selected.
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 "directory" 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 directory, or a path name relative to the stdlib directory of OCaml (written "^path" or "+path").
The variable "requires" specifies the list of required packages. The names of the packages must be separated by white space and/or commas.
The variable "version" specifies the version string.
The variable "archive" specifies the list of archive files. These files should be given as plain names without any directory information; they are only searched in the package directory. 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.
The variable "linkopts" specifies additional linker options.
The variable "description" may include a short description of the package (displayed by ocamlfind list).
It is possible to define additional variables but there is currently no software interpreting them.
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.
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 "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 automatic 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.