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Loop Expressions

SARL provides four types of loop statements.

1. For-Each Loop

The for loop is used to execute a certain expression for each element of an array or an instance of Iterable.

The for’s variable is local and final, hence cannot be updated.

The type of a for loop is void. The type of the local variable can be inferred from the iterable or array that is processed, e.g. in the following example v is of type String.

var tab : String[]
for (v : tab) {
	println(v)
}

You could specify the expected type for the local variable with the as following the local variable:

for (v as String : tab) {
	println(v)
}

2. Traditional Java For Loop

The traditional for loop is very similar to the one known from Java, or even C. When executed, it first executes the init-expression, where local variables can be declared. Next the predicate is executed and if it evaluates to true, the body-expression is executed. On any subsequent iterations the update-expression is executed instead of the init-expression. This happens until the predicate returns false. The type of a for loop is void.

for (var i = 0; i<123; i++) {
	println(i)
}

3. While Loop

A while loop is used to execute a certain expression unless the predicate is evaluated to false. The type of a while loop is void.

var i = 0
while (i<123) {
	println(i)
	i++
}

4. Do-While Loop

A while loop is used to execute a certain expression unless the predicate is evaluated to false. The difference to the while loop is that the execution starts by executing the block once before evaluating the predicate for the first time. The type of a while loop is void.

var i = 0
do {
	println(i)
	i++
}
while (i<123)

5. Breaking a loop

The break keyword is provides for breaking the enclosing loop. When this keyword is run, the control flow exits for the nearest enclosing loop, and run the statement that is just following the loop expression in the sequence of instructions.

for (v : tab) {
	if (v == 1) {
		break
	}
}

6. Jump to the next iteration

The continue keyword is provides for stopping the execution of the current iteration into loop, and jumping to the next iteration. When this keyword is run, the control flow jumps to the next iteration for the nearest enclosing loop, and run the statement that is just at the beginning of the loop’s block expression.

for (v : tab) {
	if (v == 1) {
		continue
	}
}

7. Acknowledgements

This documentation is inspired by the documentations from the Xtext and Xtend projects.

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