Perl 6 Deep Dive

On-demand supplies

The data flow of supplies contains two parts—the supplier that emits data and the tap that receives it. Perl 6's reactive programming model is a thread-safe implementation of the Observer design pattern.

Let us create our first on-demand supply using the supply keyword:

supply {    emit($_) for 'a'..'e';}

The supply is here but it does not emit any data yet because there is no demand. You can easily see this if you add a print instruction to the loop:

supply {    for 'a'..'e' {        emit($_);         say "Emitted $_";    }}sleep 2;

The program just silently quits after 2 seconds.

To make the supply generate data, we need to create a tap. The supply block returns a value of the Supply type, and you can call the tap method on it to pass the code ...