EXPR while EXPR;

##</code><code>##

EXPR while ( EXPR );

##</code><code>##

>perl -MO=Deparse -e"while() { print 1 }"
while (1) {
    print 1;
}
-e syntax OK

>perl -MO=Deparse -e"print 1 while;"
syntax error at -e line 1, at EOF
-e had compilation errors.