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While a condition block is TRUE, evaluates another block.
The while function repeats the evaluation of its two block arguments while the first block returns true. The first block is the condition block, the second block is the evaluation block. When the condition block returns false or none!, the expression block will no longer be evaluated and the loop terminates.
The general form is:
while [cond] [body]
num: 0 while [num < 3] [ print num num: num + 1 ] 0 1 2
color: [red green blue] while [not tail? color] [ print first color color: next color ] red green blue
Here is an example using a string series:
str: "abc" while [not tail? str: next str] [ print ["length of" str "is" length? str] ] length of abc is 3 length of bc is 2 length of c is 1
The condition block can contain any number of expressions, so long as the last expression returns the condition. To illustrate this, the next example adds a print to the condition block. This will print the index value of the color. It will then check for the tail of the color block, which is the condition used for the loop.
color: [red green blue] while [ print index? color not tail? color ][ print first color color: next color ] 1 red 2 green 3 blue 4
The last value of the block is returned from the while function.
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