Perl 6 Deep Dive

Combining promises

In real programs, more than one promise can be used. Combining different promises can give very expressive ways of coding complex relationships between different parts of the code.

Let us start with a simple example and create three promises using the standalone start function:

say 'Start';await    start {sleep 2; say 2;},    start {sleep 3; say 3;},    start {sleep 1; say 1;};say 'Done';

The goal is to pause the program until all the promises are kept. As you can see from this example, the await function accepts a list of promises and waits until all of them are completed. The output of the program looks like this:

Start123Done

Each promise creates a separate thread, which can be clearly seen by printing the $*THREAD variable: ...