BT_TRAVERSAL(1) btparse BT_TRAVERSAL(1)NAMEbt_traversal - AST traversal/query functions in btparse library
SYNOPSIS
AST * bt_next_entry (AST * entry_list,
AST * prev_entry)
AST * bt_next_field (AST * entry, AST * prev, char ** name)
AST * bt_next_value (AST * head,
AST * prev,
bt_nodetype_t * nodetype,
char ** text)
bt_metatype_t bt_entry_metatype (AST * entry)
char * bt_entry_type (AST * entry)
char * bt_entry_key (AST * entry)
char * bt_get_text (AST * node)
DESCRIPTION
The functions described here are all used to traverse and query the
abstract-syntax trees (ASTs) returned by the input functions described
in bt_input. The three "bt_next" functions ("bt_next_entry()",
"bt_next_field()", and "bt_next_value()") are used respectively to
traverse a list of entries, the list of fields within a particular
entry, and the list of simple values associated with a particular
field. The other functions are just used to query various nodes in the
tree for the useful information contained in them.
Traversal functions
bt_next_entry()
AST * bt_next_entry (AST * entry_list,
AST * prev_entry)
Used to traverse the linked list of entries returned by
"bt_parse_file()" (see bt_input). On the first call, you should
supply "NULL" for "prev_entry", and a pointer to the head of the
list will be returned. On subsequent calls, pass the previous
return value as "prev_entry"; the function returns the next entry
in the list, or "NULL" if there are no more entries. Also returns
"NULL" if either "entry_list" or "prev_entry" are improper.
For example (ignoring error handling and variable declarations):
entries = bt_parse_file (filename, options, &status);
entry = NULL;
while (entry = bt_next_entry (entries, entry))
{
/* process entry */
}
bt_next_field()
AST * bt_next_field (AST * entry, AST * prev, char ** name)
Used to traverse the list of fields in a regular or macro
definition entry. (You should call "bt_entry_metatype()" to
determine if you have the right kind of entry before calling
"bt_next_field()".) "entry" should be a pointer to the AST for a
single entry, as returned by "bt_parse_entry()",
"bt_parse_entry_s()", or "bt_next_entry()". On the first call,
supply "NULL" for "prev"; "bt_next_field()" will return a pointer
to the first field in "entry", or "NULL" if "entry" has no fields
(for instance, if it's a comment or preamble entry). On subsequent
calls, pass the previous return value as "prev"; "bt_next_field()"
will keep returning pointers to field sub-ASTs as long as it makes
sense. These pointers can then be passed to "bt_next_value()" or
"bt_get_text()" to get the field's value.
For example, the loop body in the previous example could be:
field = NULL;
while (field = bt_next_field (entry, field, &field_name))
{
/* process field */
}
bt_next_value()
AST * bt_next_value (AST * head,
AST * prev,
bt_nodetype_t * nodetype,
char ** text)
Traverses the list of simple values that make up the value of a
single field. (Recall that a simple value is either a quoted
string, a macro invocation, or a number. A compound value is a
list of these separated by '#' in the original input. Depending on
the string post-processing options used when the data was parsed,
the "list of simple values" nature of the original data may be
preserved in the AST that you're traversing, in which case you'll
need a "bt_next_value()" loop.
"bt_next_value()" works much like "bt_next_entry()" and
"bt_next_field()": on the first call, you supply "NULL" for "prev",
and on subsequent calls you supply the previous return value.
Returns "NULL" when there are no more simple values to return.
Also sets *nodetype and *text to the corresponding information from
the simple value node. *nodetype will be one of "BTAST_STRING",
"BTAST_MACRO", or "BTAST_NUMBER"; *text will point to the same
string as the AST node does (it is not copied for you), so don't
mess with it.
For example, the loop body in the "bt_next_field()" example could
be replaced with:
value = NULL;
while (value = bt_next_field (field, value, &nodetype, &text))
{
switch (nodetype)
{
case BTAST_STRING: /* process the string */
case BTAST_MACRO: /* process the macro */
case BTAST_NUMBER: /* process the number */
}
}
See also "bt_get_text".
Query functions
bt_entry_metatype()
bt_metatype_t bt_entry_metatype (AST * entry)
Returns the metatype of an entry. (Recall that the metatype is an
enumerated type whose values are derived from the specific type of
an entry; for instance, an @comment entry has type "comment" and
metatype "BTE_COMMENT". The type-metatype relationship is
similarly obvious for "BTE_PREAMBLE"; "BTE_MACRODEF" corresponds to
@string entries; and "BTE_REGULAR" corresponds to any other type.)
Returns "BTE_UNKNOWN" if "entry" is invalid (i.e., "NULL" or not a
pointer to an entry AST).
bt_entry_type()
char * bt_entry_type (AST * entry)
Returns the type of an entry. Recall that the type is the name
that appears after the '@' character in the original input.
Returns "NULL" if "entry" is invalid (i.e., "NULL" or not a pointer
to an entry AST).
bt_entry_key()
char * bt_entry_key (AST * entry)
Returns the citation key of a regular entry. (The citation key is
the name that appears after the entry-open delimiter in a regular
entry.) Returns "NULL" if "entry" is invalid (i.e., "NULL" or not
a pointer to the AST for a regular entry).
bt_get_text()
char * bt_get_text (AST * node)
Performs all string post-processing (macro expansion, concatenation
of simple values, and whitespace collapsing) of a compound value
and returns the string that results. Can be called either on a
field for a regular or macro definition entry (as returned by
"bt_next_field()"), or on a comment or preamble entry. Returns
"NULL" if called on an invalid AST node.
SEE ALSO
btparse, bt_input, bt_postprocess
AUTHOR
Greg Ward <gward@python.net>
btparse, version 0.71 2015-05-28 BT_TRAVERSAL(1)
