Ox version 1.10.1 is now available on SourceForge (sourceforge.net/projects/ox-attribute-grammar-compiler/).
Ox generalizes the function of Yacc in the way that an attribute grammar generalizes a context-free grammar. Ordinary Yacc and Lex specifications may be augmented with definitions of synthesized and inherited attributes written in C/C++ syntax. Ox checks these specifications for consistency and completeness, and generates from them a program that builds and decorates attributed parse trees. The user may specify post-decoration traversals for easy ordering of side effects, such as code generation. Ox handles the
tedious and error-prone details of writing code for parse-tree management, so its use eases problems of security and maintainability associated with that aspect of translator development.
Ox NEWS
* Noteworthy changes in release 1.10.1 (1 Feb 2022)
** Internals
This release continues the upgrade of the Ox source from C99 to C++11.
The Ox internal 'stringTable []' implementation was changed to use the 'std::unordered_map' container. The generation of 'yyyStringTab [] from the contents of 'stringTable []' was changed to eliminate empty entries.
The code generation architecture was restructured:
- The C 'typedef union target * targetT' pun (aka hack) was replaced with a class hierarchy, with abstract base class 'outMgr'.
- The use of C global 'FILE *' variables and C standard library file
management functions was replaced by a 'std::iostream *' member in class 'outMgr' and the respective member functions for output.
- Classes derived from 'outMgr' unify output to files (using a 'std::fstream
*' member) and in-memory buffers (using a 'std::stringstream *' member).
- The generation of '#line' directives was simplified, replacing the 'targetT' pun's set of 'lex* ()' and ‘gen* ()' text output functions with a set of overloaded 'put ()' text output functions.
- Calls to 'put ()' are preceded by a call to 'lex ()' (for input file '#line' directives) or 'gen ()' (for output file '#line' directives), as required.
- The deferred blank line ring buffer complexity was simplified to just count blank lines submitted for output, but not yet written.
- Blank lines (up to a maximum) are actually written to the output when switching between writing non-blank *as-is* input text and generated text,
with '#line' directives written, as required.
- Other code generation function name prefixes 'gen' and 'print' were replaced with 'put' for unifority.
The lexer specifications are now processed by 'flex++':
- The use of C global 'FILE *' variables and C standard library file
management functions was replaced with 'std::ifstream' objects and the respecitive member functions for input.
- The custom 'YY_INPUT ()' macro used with 'flex'-generated lexer source was replaced with an overriden 'LexerInput ()' implementation to handle the
Windows "\r\n" EOL sequence.
- The custom input buffer stack management was replaced with the 'flex' standard input buffer stack management.
The following additional changes were made to the lexer specifications:
- A number of individual pattern rules with the same action were combined into a single pattern rule using the '|' pattern alternative operator, for
clarity.
- The use of 'unput ()' was replaced with 'yyless ()', for efficiency.
- A number of trailing context pattern rules were rewritten to eliminate the trailing context, for efficiency.
** Bug fixes
Occurrences of unmatched ` and ' characters in // comments, which cause 'flex++' version 2.6.2 to run off the end of the specification file, were either removed or paired to avoid the issue.
The error message string created for failure to erase a file was left in a global 'std::stringstream' buffer if the erase operation succeeded.
Subsequent use of that global buffer for an error message contained the erase failure message text.
The Y-file lexer was corrected to return the 'RBRACE' token for a '}'
character in the Yacc definition section (not associated with a "%<directive>
{ ... }" C code block, which would normally never occur); it was incorrectly returning the 'LBRACE' token.
The tree visualization skeleton was missing "#include <cassert>" (for a C++ compile) or "#include <assert.h>" (for a C compile).
If Ox is configured for a single target parser (e.g., with the option "--enable-target=bison"), only that corresponding target parser header file (e.g., '#include "agc-bison.hh"') is now processed when compiling './source/main.cc'.
A typographical error in an attribute evaluation expression (a + operator in the expression should have been a - operator) was corrected in the '*calc*' test cases.
The test suite cleanup configuration where the 'bison' version is < 3.5.4 was corrected.
The './configure' script check for the presence of the C++ header
'FlexLexer.h' in the MinGW environment was corrected to look in the '/usr/include' system directory. If 'flex++' is used in the MinGW
environment, the 'AM_CPPFLAGS' Automake variable is augmented with "-idirafter /usr/include" so the MinGW C++ compilers can find 'FlexLexer.h' at compile time.
The './configure' script was corrected to extract the 'flex' version number regardless of the executable's name.
** Build system
The C++ header 'FlexLexer.h' from the 'flex' distribution used to generated
the distributed lexer C++ source was added to the './source' distribution directory. The 'FlexLexer.h' file installed in other environments may not match the distributed source, causing C++ compile failure.
The './configure' script check for C++ compiler support for the "-std=gnu++11|14|17" option was changed to "-std=c++11|14|17".
The Automake 'BUILT_SOURCES' variable is now only set if Ox is configured with the "--enable-maintainer-mode" option.
The lexer generation Make rule is now only enabled if Ox is configured with
the "--enable-maintainer-mode" option.
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