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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
- - 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