exercism/elixir/rpn-calculator-inspection/HINTS.md

Hints

General

• Read about links and tasks in the official Getting Started guide.
• Take a look at the documentation of the Task module.
• Read "Demystifying processes in Elixir" on blog.appsignal.com.
• Read "Understanding Exit Signals in Erlang/Elixir" on crypt.codemancers.com.

1. Start a reliability check for a single input

• You don't need a task for this step, a regular linked process is enough.
• There is a built-in function that runs a given anonymous function in a new process and links it to the current process.

2. Interpret the results of a reliability check

• To receive a single message, call receive once. It will read the first message that matches any of the given patterns, leaving other messages in the process inbox.
• Either a guard or the pin operator can be used to ensure that only messages from a process whose PID matches the PID given to await_reliability_check_result/2 as an argument will be received.
• receive accepts an after clause to handle timeouts.

3. Run a concurrent reliability check for many inputs

• The current process must start trapping exits before any new linked processes are spawned.
• Trapping exits in a process is achieved by setting a flag on that process.
• There is a built-in function that sets a flag on a process and returns the old value of that flag.
• The flag for trapping exits is called :trap_exit and accepts a boolean value.
• Make use of Enum functions to first start a process for each input, and then await messages from each process. Use the functions implemented in the two previous steps. Note that the map returned by start_reliability_check/2 matches the map that await_reliability_check_result/2 expects as the first argument.

4. Run a concurrent correctness check for many inputs

• Use an asynchronous task for this step.
• There is a built-in function that starts an asynchronous task.
• There is a built-in function that waits for an asynchronous task to finish executing and returns its result. It accepts a timeout as a second argument.
• Make use of Enum functions to first start a task for each input, and then wait for each task.