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+# $Id: interactive_calculator.tac,v 1.2 2004/09/08 21:38:44 tang Exp $
+
+# This example expands the simple calculator to be interactive from
+# the command line.  Note the use of an empty rule (i.e., epsilon
+# transition).  Also featured are the error token and error recovery.
+
+%{
+#!/usr/bin/tclsh
+
+%}
+
+%token ID NEWLINE
+
+%%
+
+start: line NEWLINE start
+ | line
+ ;
+
+line: E       { puts " = $1" }
+ | error      { puts " -- error" }
+ |   # empty
+ ;
+ 
+E: E '+' T    { set _ [expr {$1 + $3}] }
+ | E '-' T    { set _ [expr {$1 - $3}] }
+ | T
+ ;
+
+T: T '*' F    { set _ [expr {$1 * $3}] }
+ | T '/' F    { set _ [expr {$1 / $3}] }
+ | F
+ ;
+ 
+F: '(' E ')'  { set _ $2 }
+ | ID         { set _ $::yylval }
+ ;
+ 
+%%
+
+source simple_scanner.tcl
+yyparse