Introducing Elixir: Getting Started in Functional Programming by Simon St. Laurent & J. David Eisenberg

Author:Simon St. Laurent & J. David Eisenberg
Language: eng
Format: epub, pdf
Publisher: O'Reilly Media
Published: 2016-12-22T00:00:00+00:00

iex(1)> pid1 = spawn(MphDrop, :mph_drop, []) #PID<0.47.0> iex(2)> send(pid1, {:earth, 20}) On earth, a fall of 20 meters yields a velocity of 44.289078952755766 mph. {:earth,20} iex(3)> send(pid1, {:mars, 20}) On mars, a fall of 20 meters yields a velocity of 27.250254686571544 mph. {:mars,20}

This simple example might look like it behaves as a more complex version of a function call, but there is a critical difference. In the shell, with nothing else running, the result will come back quickly — so quickly that it reports before the shell puts up the message — but this was a series of asynchronous calls. Nothing held and waited specifically for a returned message.

The shell sent a message to pid1, the process identifier for MphDrop.convert/1. That process sent a message to drop_pid, the process identifier for Drop.drop/0, which MphDrop.mph_drop/0 set up when it was spawned. That process returned another message to MphDrop.convert/1, which reported to standard output (in this case, the shell). Those messages passed and were processed rapidly, but in a system with thousands or millions of messages in motion, those passages might have been separated by many messages and come in later.

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