word WordComm( word u, word w )
{
word x;
x = Commutator( u, w );
Free( u );
Free( w );
return x;
}
/*
** Atom() reads an atom. Note that Atom() creates a generator by
** calling GenNumber().
**
** The defining rule for atoms is:
**
** atom: 'generator' | '(' word ')' | commutator
*/
static node *Atom(void) {
node *n = 0;
if (Token == GEN) {
n = GetNode(TGEN);
n->cont.g = GenNumber(Gen, NOCREATE);
if (n->cont.g == (gen)0) SyntaxError("Unkown generator");
NextToken();
} else if (Token == LPAREN) {
NextToken();
n = Word();
if (Token != RPAREN)
SyntaxError("Closing parenthesis expected");
NextToken();
} else if (Token == LBRACK) {
n = Commutator();
} else {
SyntaxError("Generator, left parenthesis or commutator expected");
}
return n;
}