Control flow

Branch and repeat computations using runtime values. Begin with a condition, then introduce a loop whose state changes on each iteration.

Conditions and branches

if selects its body when the condition is true; else provides the alternative.

var total = 0
var odd_count = 0
var index = 0
while index < 5 {
    if index % 2 == 0 {
        total += index
    } else {
        odd_count += 1
    }
    index += 1
}
assert total == 6
assert odd_count == 2

Loops and scopes

while checks its condition before each iteration. Update a value that affects the condition to make progress. Branch and loop bodies create lexical value scopes; assignment can update an existing binding in an outer scope.

Return from a function

Inside a compiled function, return supplies the declared result and exits the call. Use a small function when a repeated calculation deserves a name; continue with Functions.