While Loops

Syntax#

while (boolean_expression) { block_expression }
do { block_expression } while (boolean_expression)

Parameters#

Parameter	Details
`boolean_expression`	Any expression that will evaluate to `true` or `false`.
`block_expression`	Any expression or set of expressions that will be evaluated if the `boolean_expression` evaluates to `true`.
## Remarks#
The primary difference between `while` and `do-while` loops is whether they execute the `block_expression` before they check to see if they should loop.

Because while and do-while loops rely on an expression to evaluate to false to terminate, they often require mutable state to be declared outside the loop and then modified inside the loop.

While Loops

var line = 0
var maximum_lines = 5

while (line < maximum_lines) {
  line = line + 1
  println("Line number: " + line)
}

Do-While Loops

var line = 0
var maximum_lines = 5

do {
  line = line + 1
  println("Line number: " + line)
} while (line < maximum_lines)

The do/while loop is infrequently used in functional programming, but can be used to work around the lack of support for the break/continue construct, as seen in other languages:

if(initial_condition) do if(filter) {
  ...
} while(continuation_condition)