Yacc neophyte vs inscrutable error message

[Kenneth Almquist]

mark at sickkids.UUCP (Mark Bartelt) writes:
> [Message from YACC:]
>  fatal error: default action causes potential type clash, line xxx

When you omit an action, YACC supplies the default action {$$ = $1}.
You get the above message if $$ and $1 have different types.  The
line number may refer to the start of the rule following the rule that
is in error.
				Kenneth Almquist