Enums in Chapel

Our enum type ServerState has an underlying integer type. The possible values for ServerState are defined as constants.

By implementing the fmt.Stringer interface, values of ServerState can be printed out or converted to strings.

In Chapel, enums can be created and used similarly to other languages. Here’s how you can achieve the same functionality.

// Define an enum
enum ServerState {
    StateIdle,
    StateConnected,
    StateError,
    StateRetrying
}

// Define a dictionary to map enum values to their string representations
var stateName: [ServerState] string = (StateIdle: "idle", StateConnected: "connected", StateError: "error", StateRetrying: "retrying");

// Create a method to convert enum values to their string representations
proc ServerState.toString() {
    return stateName[this];
}

// transition function to change states
proc transition(s: ServerState): ServerState {
    select s {
    when StateIdle do
        return StateConnected;
    when StateConnected, StateRetrying do
        return StateIdle;
    when StateError do
        return StateError;
    otherwise
        compilerError("unknown state: ", s);
    }
}

proc main() {
    var ns = transition(StateIdle);
    writeln(ns.toString());

    var ns2 = transition(ns);
    writeln(ns2.toString());
}

To run the program, you need to compile the code and run the resulting executable.

$ chpl enums.chpl -o enums
$ ./enums
connected
idle

The transition function simulates a state transition for a server. It takes the existing state and returns a new state based on predefined conditions. This provides some degree of compile-time type safety for enums.

Interfaces in Chapel

Struct Embedding in Chapel

Learn X By Example

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Enums in Chapel