Generators

Make a finite array

[1 |+ 2 |; 5] begins at 1, adds 2 each time, and returns five values. The starting value counts. |; produces the finished array immediately.

Runnable RiXRun cell

[1 |+ 2 |; 5];

The result is [1, 3, 5, 7, 9]. Change the step to 3, then predict all five values before running it.

Use a named count

You can choose the count elsewhere in a program. An array is one-based, so the fourth item of this four-value result is 7.

Runnable RiXRun cell

count := 4; values := [1 |+ 2 |; count]; values[4];

Set a finite count deliberately: a generator without a bound may continue producing values until the caller stops asking for them. For mapping or filtering an array, see Pipes.

When values should be lazy

Replacing |; with |^ creates a lazy sequence with a known length. It shows a sequence description until you ask for an item.

Runnable RiXRun cell

later := [1 |+ 2 |^ 5]; later[5];

The requested fifth value is still 9. Lazy generators explains when and how to inspect them safely. Continue to Pipes to transform a finite result.