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+Copyright
+---------
+taccle itself is protected by the GNU General Public License.  See the
+file COPYING for details.  Of course, any code you generate using
+taccle is subject to whatever restrictions you place on it.
+
+
+Availability
+------------
+A wiki page for taccle may be found at http://mini.net/tcl/taccle.
+An archive of taccle files are available at http://tcl.jtang.org/taccle.
+
+
+taccle README
+-------------
+taccle is another compiler compiler for the Tcl language.  It takes as
+input a "taccle specification file"; from this taccle generates a Tcl
+file that implements an LALR(1) parser.  The program brings to the Tcl
+language what yacc and bison do for C and C++.
+
+This release of taccle implements nearly all features of yacc:
+ - %token and %start declarations
+ - %define parse.error verbose declaration
+ - epsilon transitions (i.e., "empty" rules)
+ - embedded (mid-rule) actions
+ - literal tokens
+ - symbol values and synthesized attributes
+ - the error token and error recovery
+ - shift/reduce and reduce/reduce conflict notification
+ - operator precedence with %left, %right, %nonassoc, and %prec
+ - functions yyerror, YYABORT, YYACCEPT, and yyclearin
+ - infinite recursion detection
+
+Features currently missing in taccle are:
+ - inherited attributes
+ 
+Because taccle uses the lset command it requires Tcl 8.4 or greater.
+
+Be aware of the following differences between taccle and yacc:
+
+1. taccle (and Tcl) has no concept of variable types.  Thus %union and
+   %type declarations are no longer needed.
+
+2. yacc uses variables $1, $2, etc for symbol values; it uses $$ for
+   the synthesized attribute.  Although both $1 and $$ are legal
+   variable references in Tcl the latter is more awkward; the
+   expression `set $ foo' is not legal.  Instead of $$ use the name
+   '_', as in `set _ foo'.  These variables' scopes are valid only
+   within the context of an action.  See
+   examples/simple_calculator.tac for an example.
+
+   (The astute observer notes that using $_ for synthesized values is
+   similar to Perl's use of the auto-variable $_.)
+
+3. taccle has error handling just like bison.  It always declares the
+   terminal `error' that is pushed onto the stack whenever it detects
+   a syntax error.  Although yyclearin is implemented neither
+   YYRECOVERING nor yyerrok are.  The example
+   interactive_calculator.tac implements error handling.
+
+4. Like yacc, taccle requires a token generator.  The examples use
+   fickle (http://mini.net/tcl/fickle), though others are welcome.
+
+5. taccle calls a global function yylex to fetch the next token.  This
+   yylex function is expected to return the next token in the input
+   stream, either a string or a number.  Normally this poses no
+   problem except for the case of a literal zero.  Tcl makes no
+   distinction between the integer zero and the string zero.  Because
+   zero is reserved for the end of input marker, taccle will refuse
+   grammars that employ literal zeros.  You can get around this by
+   declaring `%token ZERO' and using that instead.
+
+6. Another literal that causes all sorts of problems is the open brace
+   '{'.  Because most things are represented internally as lists the
+   presence of the brace breaks everything.  Thus taccle will refuse
+   to parse grammars with this literal; you'll have to use a %token
+   instead.
+
+   
+Using the Examples
+------------------
+Execute taccle as if it were yacc:
+
+  $ tclsh ./taccle.tcl -d some_spec_file.tac
+
+This will generate two files, some_spec_file.tcl and
+some_spec_file.tab.tcl.  The first contains the actual parser code;
+execute it by calling yyparse.  The latter file is file to be sourced
+by the lexer, much akin to yacc's y.tab.h file.
+
+The Makefile in the examples subdirectory will generate two simple
+calculator programs.  You will need a copy of fickle (available at
+http://mini.net/tcl/fickle) and may need to modify its location on
+line 4 of the Makefile.  After filtering simple_calculator through
+ficcle and taccle execute it like so:
+
+  $ echo "6*9" | tclsh simple_calculator.tcl
+
+If all goes well the program displays:
+
+  Result is 54
+
+A more interesting example is interactive_calculator.tcl.  This one is
+designed to handle any arbitrary number of commands.  Upon errornous
+equations it recovers by discarding the rest of the buffer.  Here is
+an example session of it:
+
+  $ tclsh interactive_calculator.tcl
+  6*9
+   = 54
+  1++2++3
+   = error
+  1 + 2 + 3
+   = 6
+
+The final example, infix_calc.tcl, shows how to use operator
+precedence to resolve shift/reduce conflicts.  It understands both
+left associative operators (addition et al) as well as right
+associative (exponentation).  Here is an example use:
+
+  $ echo "2^2^2 - 10 * 2 + 6 / 3" | tclsh infix_calc.tcl
+          -2