-* The Yacc prologue alternatives from Bison 2.3a have been rewritten as the
- following directives:
-
- 1. %code {CODE}
-
- Other than semantic actions, this is probably the most common place you
- should write verbatim code for the parser implementation. It replaces
- the traditional Yacc prologue, `%{CODE%}', for most purposes. Compare
- with:
-
- - `%{CODE%}' appearing after the first `%union {CODE}' in a grammar
- file. While Bison will continue to support `%{CODE%}' for backward
- compatibility, `%code {CODE}' is cleaner as its functionality does
- not depend on its position in the grammar file relative to any
- `%union {CODE}'. Specifically, `%code {CODE}' always inserts your
- CODE into the parser code file after the usual contents of the
- parser header file.
- - `%after-header {CODE}', which only Bison 2.3a supported.
-
- 2. %requires {CODE}
-
- This is the right place to write dependency code for externally exposed
- definitions required by Bison. Such exposed definitions are those
- usually appearing in the parser header file. Thus, this is the right
- place to define types referenced in `%union {CODE}' directives, and it
- is the right place to override Bison's default YYSTYPE and YYLTYPE
- definitions. Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
- file. Unlike `%{CODE%}', `%requires {CODE}' inserts your CODE both
- into the parser code file and into the parser header file since
- Bison's required definitions should depend on it in both places.
- - `%start-header {CODE}', which only Bison 2.3a supported.
-
- 3. %provides {CODE}
-
- This is the right place to write additional definitions you would like
- Bison to expose externally. That is, this directive inserts your CODE
- both into the parser header file and into the parser code file after
- Bison's required definitions. Compare with:
-
- - `%end-header {CODE}', which only Bison 2.3a supported.
-
- 4. %code-top {CODE}
-
- Occasionally it is desirable to insert code near the top of the parser
- code file. For example:
-
- %code-top {
- #define _GNU_SOURCE
- #include <stdio.h>
- }
-
- Compare with:
-
- - `%{CODE%}' appearing before the first `%union {CODE}' in a grammar
- file. `%code-top {CODE}' is cleaner as its functionality does not
- depend on its position in the grammar file relative to any
- `%union {CODE}'.
- - `%before-header {CODE}', which only Bison 2.3a supported.
-
- If you have multiple occurrences of any one of the above four directives,
- Bison will concatenate the contents in the order they appear in the grammar
- file.
-
- The prologue alternatives are experimental. More user feedback will help to
- determine whether they should become permanent features.
-
- Also see the new section `Prologue Alternatives' in the Bison manual.
-
projects / bison.git / blobdiff