Assignment Expression Grammar

"Grammar for Jack Crenshaw's Assignment Expression Parser (Part 3):
  "<assignment>  ::=  <name> = <expression>
  "<expression>  ::=  <term> ( <add> | <subtract> )*
  "<subtract>    ::=  '-' <term>
  "<add>         ::=  '+' <term>
  "<term>        ::=  <factor> ( <multiply> | <divide> )*
  "<divide>      ::=  '/' <factor>
  "<multiply>    ::=  '*' <factor>
  "<factor>      ::=  <number> | '(' <expression> ')' | <ident>
  "<ident>       ::=  <func> | <name>
  "<func>        ::=  <name> '(' ')'
  "<name>        ::=  <alpha> <alphanum>*
  "<alpha>       ::=  [a-zA-Z_]
  "<alphanum>    ::=  <alpha> | <digit>
  "<number>      ::=  <digit>+
  "<digit>       ::=  [0-9]