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Diffstat (limited to 'contrib/byacc/NOTES-btyacc-Disposition')
| -rw-r--r-- | contrib/byacc/NOTES-btyacc-Disposition | 80 |
1 files changed, 0 insertions, 80 deletions
diff --git a/contrib/byacc/NOTES-btyacc-Disposition b/contrib/byacc/NOTES-btyacc-Disposition deleted file mode 100644 index 98e527b..0000000 --- a/contrib/byacc/NOTES-btyacc-Disposition +++ /dev/null @@ -1,80 +0,0 @@ -Tom Shields, March 17, 2014 - -NOTE: README.BTYACC needs to be re-written (or another README file created) -to explain how the extensions were adopted into the byacc-20140101 baseline. - -bytacc changes adopted; see README.BTYACC for details. ------------------------------------------------------- - - Changes to the skeleton to send debugging output to stderr. - - Changes to the types of the grammar tables from 'short' to 'int' if -MAXTABLE is defined to be > MAXSHORT for generation of large grammar tables -for large grammars. This can be set with the invocation of configure -using the --with-max-table-size=N option - - Changes to add syntactic sugaring for definition and semantic processing -of inherited attributes associated with non-terminal symbols on the rhs of -rules. Inherited attributes are implemented as {}-actions, and as such may -introduce reduce/reduce conflicts. The advantage over manual {}-actions is -that checking is performed on the number and types of inherited attributes, -and the positions on the semantic stack are automatically calculated. -Identical actions produced by the inherited attribute syntax are collapsed -into a single action, reducing reduce/reduce conflicts. - - The %type specification is extended to define the types of inherited -attributes associated with non-terminal symbols on the lhs of rules, in -addition to its original purpose in yacc for specifying the type of the -symbol itself on the parser's value stack. In order to permit the two - aspects to be used independently, the <type> specification following -%type is optional. - - Added a mechanism to the parser skeleton for computing and propagating -the text position of grammar symbols if %locations directive is present in -the grammar specificaion, or if yacc is invoked with the -L flag. Includes -support for "@$" and "@N" (for N an integer) in actions to refer to symbol -locations. - - Added a bison compatible %destructor directive to define a memory -management mechanism to the parser skeleton that enables cleanup of semantic -values and text positions associated with the parsing stack that are -automatically discarded during error processing. - -The following is only available if configure is invoked with the ---enable-btyacc=yes: - - Changes to enable backtracking with semantic disambiguation, if yacc is -invoked with the -B flag. A yacc parser disambiguates shift/reduce conflicts -by choosing to shift, and reduce/reduce conflicts by reducing using the -earliest grammar rule (in the grammar specification). A btyacc parser handles -a conflict by remembering the current parse point and entering into trial parse -mode. In trial parse mode, the parser tries each of the conflicting options -until the first successs or until all options are exhausted. If the parser -runs into an error while in trial parse mode, it backtracks to the most recent -conflict point and tries the next alternative. If the parser finds a -successful parse, it backtracks to the point where it first entered trial parse -mode and continues with normal parsing, using the action at the start of the -successful trial path. Success in trial parse mode is achieved either by -successfully reducing the start symbol at the end of input or by invocation of -YYVALID (or YYVALID_NESTED). Semantic disambiguation is supported within -[]-actions, which are always executed, with invocation of YYERROR to terminate -a trial path or YYVALID (and YYVALID_NESTED). Yacc {}-actions are only -executed during normal parsing. - - -btyacc changes deferred: ------------------------- - - The -S command line flag to enable use of an alternate parser skeleton, -read from an external file. - - Preprocessor statements: %define, %ifdef/%endif, %include. - - -btyacc changes rejected: ------------------------- - - The yyerror_detailed() option for error messages is replaced by the -byacc feature for specifying options paramters to yyerror(). - - C++-specific features in the parser skeleton. |
