while and each are control flow blocks that make it possible to repetitively loop through execution of the same code.


while offers a simple mechanism: it executes a block's statements over and over as long as its condition remains true. The condition is checked right away and every time after the block's statements have been performed.

For example, this code logs the same message 5 times:

mut x = 1
while x<=5
	$.log "DANGER, DANGER!! Will Robinson"

while suffix

while may be used as a control suffix following a statement:

$$.show(list.extract) while !list.isEmpty

is equivalent to:

while !list.isEmpty

break and continue

Within a while block, break or continue statements may be used to modify the loop's control flow behavior.

The break statement, placed anywhere within a while block, provides a way to stop performance of the 'while' block. break is typically accompanied with if:

while true    // without the break, this loop would run forever
	actor.walkstep  // will happen at least once
	break if keypress==0x20 // stops whenever the space bar is pressed

By contrast, the continue statement ignores all subsequent statements in the 'while' block, returning control back to the top of the while block where the conditional expression is re-evaluated.


Although while is sufficient to support any kind of loop, each offers a more convenient way to iterate over some sequence of values. As with while, each may be used as a control prefix. break and continue are supported within an each block.

Iterating over numbers

If one simply wants to iterate evenly over a range of integer or floating point numbers:

mut sum = 0
each x in 0 <= 5 // iterates:  0, 1, 2, 3, 4, 5
  sum += x
sum                // 15

Let's examine the elements of this each statement:

One may use any of the four comparison operators: <, <=, >, or >=. With the latter two, the variable will be decremented instead of incremented.

Optionally, the statement can specify a step value using by:

mut sum = 0
each x in 0 <= 10 by 2 // iterates: 0, 2, 4, 6, 7, 10
	sum += x