LVAL xleval(expr) LVAL expr; { /* check for control codes */ if (--xlsample <= 0) { xlsample = SAMPLE; oscheck(); } /* check for *evalhook* */ if (getvalue(s_evalhook)) return (evalhook(expr)); /* check for nil */ if (null(expr)) return (NIL); /* dispatch on the node type */ switch (ntype(expr)) { case CONS: return (evform(expr)); case SYMBOL: return (xlgetvalue(expr)); default: return (expr); } }