(eval, eval7, eval6, eval5, eval4, eval3, eval2, eval1):

(eval, eval7, eval6, eval5, eval4, eval3, eval2, eval1):
Accept a bool argument specifying whether to evaluate the
expression.  This is to allow short-circuit evaluation.  All
callers changed.
(null): Report that a string is zero even if it has
a form like "-0" or "00".
(eval1, eval): Use short-circuit evaluation for | and &.
(eval): Return 0 if both arguments are null or zero, instead
of returning the first argument.