Dont do command / opposite of if

Does a command exist, that works opposite of if:

//if does:
if(true){
do sth
}

//the dont do command (is that name ok?)
dont (true){
dont do
}

The command would be useless, because

if(!true) {}
//is pretty much the same as
dont(true) {}

what about the else dont?!

dont(true){
dont do
}else dont (false) {
do
}else dont (false) {
dont do     //since first else dont class is on
}

and else

dont(true) {
dont do
}else dont (true){
dont do
}else {
do    //since every dont clause is true
}

Should such a command exist? Is it ok to have as adding to all the other nice commands or shouldnt it exist, because its too confusing? what do you think?