  <form><textarea id="code" name="code">
/* description: Parses end executes mathematical expressions. */

/* lexical grammar */
%lex

%%
\s+                   /* skip whitespace */
[0-9]+("."[0-9]+)?\b  return 'NUMBER';
"*"                   return '*';
"/"                   return '/';
"-"                   return '-';
"+"                   return '+';
"^"                   return '^';
"("                   return '(';
")"                   return ')';
"PI"                  return 'PI';
"E"               