# Module Fl_metascanner

    module Fl_metascanner: sig .. end

Parses META files

    type formal_pred = [ `NegPred of string | `Pred of string ]

    type flavour = [ `Appendix | `BaseDef ]

``BaseDef` refers to META definitions using the "=" operator, and ``Appendix` refers to definitions using the "+=" operator.

    type pkg_definition = {

`` | `def_var : `string`;` | `(*` | The name of the defined variable | `*)`
`` | `def_flav : `flavour`;` | `(*` | The flavour of the definition | `*)`
`` | `def_preds : `formal_pred list`;` | `(*` | The formal predicates of the def | `*)`
`` | `def_value : `string`;` | `(*` | The value assigned to the variable | `*)`

`}`

A `pkg_definition` is expressed by the syntax

     var(p1,p2,...) = "value"

(flavour `BaseDef), or the syntax

     var(p1,p2,...) += "value"

(flavour `Appendix) in the META file. The list of predicates may be omitted. Predicates may be negated by using "-", e.g. "-x".

    type pkg_expr = {

`` | `pkg_defs : `pkg_definition list`;`
`` | `pkg_children : `(string * pkg_expr) list`;`

`}`

A value of type `pkg_expr` denotes the contents of a META file. The component `pkg_defs` are the variable definitions. The component `pkg_children` contains the definitions of the subpackages.

    exception Error of string

    val parse : Stdlib.in_channel -> pkg_expr

`parse ch:` scans and parses the file connected with channel `ch`. The file must have a syntax compatible with the META format. The return value contains the found definitions for the package and all subpackages.

`exception Error of string:` is raised on syntax errors. The string explains the error.

    val parse_lexing : Stdlib.Lexing.lexbuf -> pkg_expr

    val print_def : Stdlib.out_channel -> pkg_definition -> unit

`print_def ch def`: Outputs the definition to a channel.

    val print : Stdlib.out_channel -> pkg_expr -> unit

`print ch expr`: Outputs the package expression to a channel.

    val lookup : string -> string list -> pkg_definition list -> string

`lookup variable_name predicate_list def`:

Returns the value of `variable_name` in `def` under the assumption that the predicates in `predicate_list` hold, but no other predicates.

The rules are as follows: In the step (A), only the ``BaseDef` definitions are considered. The first base definition is determined where all predicates are satisfied and that has the longest predicate list. In the step (B) only the ``Appendix` definitions are considered. All definitions are determined where all predicates are satisfied. The final result is the concatenation of the single result of (A) and all results of (B) (in the order they are defined). A space character is inserted between two concatenated strings.

When step (A) does not find any matching definition, the exception `Not_found` is raised.

    val lookup_2 : string ->
           string list ->
           pkg_definition list ->
           string * formal_pred list

Like `lookup`, but also returns the list of predicates that had to be considered to select the particular variable definition.

    val predicate_exists : string -> pkg_definition list -> bool

`predicate_exists variable_name def`:

Whether `variable_name` is explicitly mentioned in `def`.