At least two linguistic mechanisms are necessary to make the computations in programs flexible and powerful: some means of selecting among alternative control flow paths (of statement execution) and some means of causing the repeated execution of statements or sequences of statements. Statements that provide these kinds of capabilities are called control statements. A control structure is a control statement and the collection of statements whose execution it controls. This set of statements is in turn generally structured as a block, which in addition to grouping, also defines a lexical scope.
There are two types of control flow mechanisms:
- choice -
when - loop -
loop - guard -
if
Choice type
when(){ case(condition){} case(condition){} _ {} };
when(variable){ is (value){}; is (value){}; _ {}; };
when(variable){ in (iterator){}; in (iterator){}; _ {}; };
when(variable){ has (member){}; has (member){}; _ {}; };
when(variable){ of (type){}; of (type){}; _ {}; };
when(type){ on (channel){}; on (channel){}; };
Condition
when() {
case (x == 6){ // implementation }
case (y.set()){ // implementation }
_ { // default implementation }
}
Valueation
when(x) {
is (6){ // implementation }
is (>7){ // implementation }
_ { // default implementation }
}
Iteration
when(2 * x) {
in ({0..4}){ // implementation }
in ({ 5, 6, 7, 8, }){ // implementation }
_ { // default implementation }
}
Contains
when({4,5,6,7,8,9,0,2,3,1}) {
has (5){ // implementation }
has (10){ // implementation }
_ { // default implementation }
}
Generics
when(T) {
of (int){ // implementation }
of (str){ // implementation }
_ { // default implementation }
}
Channel
when(str) {
on (channel){ // implementation }
on (channel){ // implementation }
_ { // default implementation }
}
Loop type
loop(condition){};
loop(iterable){};
Condition
loop( x == 5 ){
// implementation
};
Enumeration
loop( x in {..100}){
// implementation
}
loop( x in {..100}) if ( x % 2 == 0 )){
// implementation
}
loop( x in {..100} if (( x in somearra ) and ( x in anotherarray ))){
// implementation
}
Iteration
loop( x in array ){
// implementation
}
Guard type
The if statement can be used as guard in both when statement and loop statement:
loop( x in {..100} if (( x in somearra ) and ( x in anotherarray ))){
// implementation
}
when(x) {
is (6) if (6 of (int)){ // implementation }
is (7) if (7 in (somearray)){ // implementation }
* { // default implementation }http://spack.rtfd.io/
}