1BT_TRAVERSAL(1) btparse BT_TRAVERSAL(1)
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6 bt_traversal - AST traversal/query functions in btparse library
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9 AST * bt_next_entry (AST * entry_list,
10 AST * prev_entry)
11 AST * bt_next_field (AST * entry, AST * prev, char ** name)
12 AST * bt_next_value (AST * head,
13 AST * prev,
14 bt_nodetype_t * nodetype,
15 char ** text)
16 bt_metatype_t bt_entry_metatype (AST * entry)
18 char * bt_entry_type (AST * entry)
19 char * bt_entry_key (AST * entry)
20 char * bt_get_text (AST * node)
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23 The functions described here are all used to traverse and query the
24 abstract-syntax trees (ASTs) returned by the input functions described
25 in bt_input. The three "bt_next" functions (bt_next_entry(),
26 bt_next_field(), and bt_next_value()) are used respectively to traverse
27 a list of entries, the list of fields within a particular entry, and
28 the list of simple values associated with a particular field. The
29 other functions are just used to query various nodes in the tree for
30 the useful information contained in them.
31 Traversal functions
33 bt_next_entry()
34 AST * bt_next_entry (AST * entry_list,
35 AST * prev_entry)
36 Used to traverse the linked list of entries returned by
38 bt_parse_file() (see bt_input). On the first call, you should
39 supply "NULL" for "prev_entry", and a pointer to the head of the
40 list will be returned. On subsequent calls, pass the previous
41 return value as "prev_entry"; the function returns the next entry
42 in the list, or "NULL" if there are no more entries. Also returns
43 "NULL" if either "entry_list" or "prev_entry" are improper.
44 For example (ignoring error handling and variable declarations):
46 entries = bt_parse_file (filename, options, &status);
48 entry = NULL;
49 while (entry = bt_next_entry (entries, entry))
50 {
51 /* process entry */
52 }
53 bt_next_field()
55 AST * bt_next_field (AST * entry, AST * prev, char ** name)
56 Used to traverse the list of fields in a regular or macro
58 definition entry. (You should call bt_entry_metatype() to
59 determine if you have the right kind of entry before calling
60 bt_next_field().) "entry" should be a pointer to the AST for a
61 single entry, as returned by bt_parse_entry(), bt_parse_entry_s(),
62 or bt_next_entry(). On the first call, supply "NULL" for "prev";
63 bt_next_field() will return a pointer to the first field in
64 "entry", or "NULL" if "entry" has no fields (for instance, if it's
65 a comment or preamble entry). On subsequent calls, pass the
66 previous return value as "prev"; bt_next_field() will keep
67 returning pointers to field sub-ASTs as long as it makes sense.
68 These pointers can then be passed to bt_next_value() or
69 bt_get_text() to get the field's value.
70 For example, the loop body in the previous example could be:
72 field = NULL;
74 while (field = bt_next_field (entry, field, &field_name))
75 {
76 /* process field */
77 }
78 bt_next_value()
80 AST * bt_next_value (AST * head,
81 AST * prev,
82 bt_nodetype_t * nodetype,
83 char ** text)
84 Traverses the list of simple values that make up the value of a
86 single field. (Recall that a simple value is either a quoted
87 string, a macro invocation, or a number. A compound value is a
88 list of these separated by '#' in the original input. Depending on
89 the string post-processing options used when the data was parsed,
90 the "list of simple values" nature of the original data may be
91 preserved in the AST that you're traversing, in which case you'll
92 need a bt_next_value() loop.
93 bt_next_value() works much like bt_next_entry() and
95 bt_next_field(): on the first call, you supply "NULL" for "prev",
96 and on subsequent calls you supply the previous return value.
97 Returns "NULL" when there are no more simple values to return.
98 Also sets *nodetype and *text to the corresponding information from
99 the simple value node. *nodetype will be one of "BTAST_STRING",
100 "BTAST_MACRO", or "BTAST_NUMBER"; *text will point to the same
101 string as the AST node does (it is not copied for you), so don't
102 mess with it.
103 For example, the loop body in the bt_next_field() example could be
105 replaced with:
106 value = NULL;
108 while (value = bt_next_field (field, value, &nodetype, &text))
109 {
110 switch (nodetype)
111 {
112 case BTAST_STRING: /* process the string */
113 case BTAST_MACRO: /* process the macro */
114 case BTAST_NUMBER: /* process the number */
115 }
116 }
117 See also "bt_get_text".
119 Query functions
121 bt_entry_metatype()
122 bt_metatype_t bt_entry_metatype (AST * entry)
123 Returns the metatype of an entry. (Recall that the metatype is an
125 enumerated type whose values are derived from the specific type of
126 an entry; for instance, an @comment entry has type "comment" and
127 metatype "BTE_COMMENT". The type-metatype relationship is
128 similarly obvious for "BTE_PREAMBLE"; "BTE_MACRODEF" corresponds to
129 @string entries; and "BTE_REGULAR" corresponds to any other type.)
130 Returns "BTE_UNKNOWN" if "entry" is invalid (i.e., "NULL" or not a
132 pointer to an entry AST).
133 bt_entry_type()
135 char * bt_entry_type (AST * entry)
136 Returns the type of an entry. Recall that the type is the name
138 that appears after the '@' character in the original input.
139 Returns "NULL" if "entry" is invalid (i.e., "NULL" or not a pointer
140 to an entry AST).
141 bt_entry_key()
143 char * bt_entry_key (AST * entry)
144 Returns the citation key of a regular entry. (The citation key is
146 the name that appears after the entry-open delimiter in a regular
147 entry.) Returns "NULL" if "entry" is invalid (i.e., "NULL" or not
148 a pointer to the AST for a regular entry).
149 bt_get_text()
151 char * bt_get_text (AST * node)
152 Performs all string post-processing (macro expansion, concatenation
154 of simple values, and whitespace collapsing) of a compound value
155 and returns the string that results. Can be called either on a
156 field for a regular or macro definition entry (as returned by
157 bt_next_field()), or on a comment or preamble entry. Returns
158 "NULL" if called on an invalid AST node.
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161 btparse, bt_input, bt_postprocess
162
164 Greg Ward <gward@python.net>
165btparse, version 0.89 2023-07-21 BT_TRAVERSAL(1)