This is CORBA::IDLtree, a module that builds abstract syntax trees
from CORBA IDL.

The main export is sub Parse_File which takes an IDL input file name
as the parameter, and returns a reference to an array of references
to the root nodes constructed (or 0 if there were syntax errors.)

Parse_File uses two auxiliary data structures:
 @include_path  - Paths where to look for included IDL files
 %defines       - Symbol definitions for the preprocessor
                  (cf. the -D switch on many C compilers)
                  where -DSYM=VAL is represented as
                  $defines{SYM} = VAL. -DSYM is represented as
                  $defines{SYM} = 1.

A further export is the sub Dump_Symbols which takes the return value
of Parse_File as the parameter, and prints the trees constructed to
stdout in IDL syntax.

-----------------------------------------------------------------------------

SYMBOL TREE STRUCTURE

The following description of the structure of the symbol tree
applies to CORBA::IDLtree versions >= 1.0.  The structure
has been changed w.r.t. previous releases, for example the
INTERFACE node now has an "abstract" flag. Also, all the
scalars used as constants, e.g. $INTERFACE, have been changed to
subroutines, e.g. &INTERFACE, to better express the constness
of these values. However, it is intended to keep further
changes to the user interface to a minimum, i.e. the IDLtree
programming interface is now considered stable.


A "thing" in the symbol tree can be either a reference to a node, or a
reference to an array of references to nodes.

A node is a five-element array with the elements
 [0] => TYPE (MODULE|INTERFACE|STRUCT|UNION|ENUM|TYPEDEF...)
 [1] => NAME
 [2] => SUBORDINATES
 [3] => COMMENT  (introduced in IDLtree version 1.2)
 [4] => SCOPEREF

Some IDL types are representable as a simple numeric constant;
they do not require nodes.  We'll call these types "elementary".
Elementary types are the scalar types, e.g. boolean, short,
unsigned long long, any, string.

Other IDL types cannot be represented in this way, they require
more information. An enum, for example, requires the enumeration
literals. These types are represented as nodes. The TYPE element
contains a numeric ID identifying what IDL type the node represents.

The NAME element, unless specified otherwise, simply holds the name string
of the respective IDL syntactic item.

The SUBORDINATES element depends on the node type.
Sometimes an item in the SUBORDINATES may contain either a type ID or
a reference to the defining node; we will call that a `type descriptor'.
Which of the two alternatives is in effect can be determined via the
isnode() function.

Contents of SUBORDINATES:

 MODULE or       Reference to an array of nodes (symbols) which are defined
 INTERFACE       within the module or interface. In the case of INTERFACE,
                 element [0] in this array will contain a reference to a
                 further array which in turn contains references to the
                 parent interface(s) if inheritance is used, or the null
                 value if the current interface is not derived by
                 inheritance. Element [1] is the "abstract" flag which is
                 non-zero for interfaces declared abstract.

 INTERFACE_FWD   Reference to the node of the full interface declaration.

 STRUCT or       Reference to an array of node references representing the
 EXCEPTION       member components of the struct or exception.
                 Each member representative node is a quadruplet consisting
                 of (TYPE, NAME, <dimref>, COMMENT).
                 The <dimref> is a reference to a list of dimension numbers,
                 or is 0 if no dimensions were given.

 UNION           Similar to STRUCT/EXCEPTION, reference to an array of
                 nodes. For union members, the member node has the same
                 structure as for STRUCT/EXCEPTION.
                 However, the first node contains a type descriptor for
                 the discriminant type.
                 The TYPE of a member node may also be CASE or DEFAULT.
                 For CASE, the NAME is unused, and the SUBORDINATE contains
                 a reference to a list of the case values for the following
                 member node.
                 For DEFAULT, both the NAME and the SUBORDINATE are unused.

 ENUM            Reference to the array of enum value literals.
                 If the global variable $enable_enum_comments is set then
                 the elements in the array may be shaped differently:
                 - If the enum literal is not followed by a comment then
                   the element in the array is the enum literal as usual.
                 - If the enum literal is followed by a comment then the
                   element in the array is a reference to a tuple. In this
                   tuple, the first element is the enum literal, and the
                   second element is a reference to the comment list.
                   Thus, when generating code for the literals, it is
                   recommended to use the `ref' predicate to find out
                   which of the two alternatives is in effect for each
                   array element.

 TYPEDEF         Reference to a two-element array: element 0 contains a
                 reference to the type descriptor of the original type;
                 element 1 contains a reference to an array of dimension
                 numbers, or the null value if no dimensions are given.

 SEQUENCE        As a special case, the NAME element of a SEQUENCE node
                 does not contain a name (as sequences are anonymous
                 types), but instead is used to hold the bound number.
                 If the bound number is 0, then it is an unbounded
                 sequence. The SUBORDINATES element contains the type
                 descriptor of the base type of the sequence. This
                 descriptor could itself be a reference to a SEQUENCE
                 defining node (that is, a nested sequence definition.)
                 Bounded strings are treated as a special case of sequence.
                 They are represented as references to a node that has
                 BOUNDED_STRING or BOUNDED_WSTRING as the type ID, the bound
                 number in the NAME, and the SUBORDINATES element is unused.

 CONST           Reference to a two-element array. Element 0 is a type
                 descriptor of the const's type; element 1 is a reference
                 to an array containing the RHS expression symbols.

 FIXED           Reference to a two-element array. Element 0 contains the
                 digit number and element 1 contains the scale factor.
                 The NAME component in a FIXED node is unused.

 VALUETYPE       [0] => $is_abstract (boolean)
                 [1] => reference to a tuple (two-element list) containing
                        inheritance related information:
                        [0] => $is_truncatable (boolean)
                        [1] => \@ancestors (reference to array containing
                               references to ancestor nodes)
                 [2] => \@members: reference to array containing references
                        to tuples (two-element lists) of the form:
                        [0] => 0|PRIVATE|PUBLIC
                               A zero for this value means the element [1]
                               contains a reference to a METHOD or ATTRIBUTE.
                               In case of METHOD, the first element in the
                               method node subordinates (i.e., the return
                               type) may be FACTORY.
                        [1] => reference to the defining node.
                               In case of PRIVATE or PUBLIC state member,
                               the defining node is the same as for STRUCT
                               subordinates, namely a quadruplet containing:
                                [0] => member type id
                                [1] => member name
                                [2] => dimref (reference to dimensions list)
                                [3] => COMMENT element

 VALUETYPE_BOX   Reference to the defining type node.

 VALUETYPE_FWD   Subordinates unused.

 NATIVE          Subordinates unused.

 ATTRIBUTE       Reference to a two-element array; element 0 is the read-
                 only flag (0 for read/write attributes), element 1 is a
                 type descriptor of the attribute's type.

 METHOD          Reference to a variable length array; element 0 is a type
                 descriptor for the return type. Elements 1 and following
                 are references to parameter descriptor nodes with the
                 following structure:
                     elem. 0 => parameter type descriptor
                     elem. 1 => parameter name
                     elem. 2 => parameter mode (IN, OUT, or INOUT)
                 The last element in the variable-length array is a
                 reference to the "raises" list. This list contains
                 references to the declaration nodes of exceptions raised,
                 or is empty if there is no "raises" clause.

 INCFILE         Reference to an array of nodes (symbols) which are defined
                 within the include file. The Name element of this node
                 contains the include file name.

 PRAGMA_PREFIX   Subordinates unused.

 PRAGMA_VERSION  Version string.

 PRAGMA_ID       ID string.

 PRAGMA          This is for the general case of pragmas that are none
                 of the above, i.e. pragmas unknown to IDLtree.
                 The NAME holds the pragma name, and SUBORDINATES
                 holds a reference to all further text appearing after
                 the pragma name, if any.

 REMARK          The SUBORDINATES of the node is unused.
                 The NAME component contains a reference to a list of
                 comment lines. In the case of a single-line comment, the
                 list will contain only one element; in case of multi-
                 line comments, each line is represented by a list entry.
                 The lines in this list are not newline terminated; empty
                 entries represent empty comment lines.
 REMARK          The SUBORDINATES of the node is unused.
                 The NAME component contains a reference to a list of
                 comment info array references.  In the case of a single-
                 line comment, the list will contain only one element; in
                 case of multi-line comments, each line is represented by a
                 list entry.  A comment info array element is a triplet
                 (three element list) with [0] = filename, [1] = line
                 number, [2] = comment text.
                 The comment text (index 2) is not newline terminated; empty
                 entries represent empty comment lines.
                 The COMMENT element (described below) uses the same
                 definition of a "comment line".


The COMMENT element holds the comment text that follows the IDL declaration
on the same line. Usually this is just a single line. However, if a multi-
line comment is started on the same line after a declaration, the multi-line
comment may extend to further lines - therefore we use a list of lines.
The lines in this list are not newline terminated. The COMMENT field is a
reference to this list, or contains the value 0 if no comment is present
at the IDL item.

Comment lines are not simple strings, a reference to an array is used that
contains the name of the file, the line number and the comment text in that
order.

The SCOPEREF element is a reference back to the node of the module or
interface enclosing the current node. If the current node is already
at the global scope level then the SCOPEREF is 0.
Special case: For a reopened module, the SCOPEREF points to the previous
opening of the same module. In case of multiple reopenings, each reopening
points to the previous opening. The SCOPEREF of the initial module finally
points to the enclosing scope.
All nodes have this element except for the parameter nodes of methods and
the component nodes of structs/unions/exceptions.


-- Last updated: 2017/07/23
-- [email protected]

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