Title here
Summary here
Enums in Modelica
Our enum type ServerState has an underlying int type.
type ServerState = enumeration(StateIdle, StateConnected, StateError, StateRetrying);The possible values for ServerState are defined as constants in the enumeration. In Modelica, we define an enumeration with specific names without needing an automatic value generator like iota.
By defining a function to convert the enum value to a string, we can print out or convert ServerState values to strings.
function stateToString
input ServerState ss;
output String stateName;
algorithm
stateName := match(ss)
(ServerState.StateIdle, "idle"),
(ServerState.StateConnected, "connected"),
(ServerState.StateError, "error"),
(ServerState.StateRetrying, "retrying");
end stateToString;This function, stateToString, provides a way to convert the enumerated state values to their corresponding string representation.
The main function demonstrates how to transition between states and print them.
function transition
input ServerState s;
output ServerState nextState;
algorithm
nextState := if s == ServerState.StateIdle then
ServerState.StateConnected
else if (s == ServerState.StateConnected or s == ServerState.StateRetrying) then
ServerState.StateIdle
else if s == ServerState.StateError then
ServerState.StateError
else
error("unknown state: " + stateToString(s));
end transition;The transition function emulates a state transition for a server; it takes the existing state and returns a new state.
model Main
ServerState ns;
ServerState ns2;
algorithm
ns := transition(ServerState.StateIdle);
print(stateToString(ns));
ns2 := transition(ns);
print(stateToString(ns2));
end Main;Running this Modelica model will produce the results of the state transitions.
To run the program, compile the Modelica model using your Modelica toolchain (like OpenModelica or Dymola) and execute it.
$ omc Main.mos
$ ./Main
connected
idleModelica provides a robust way to define and manage state transitions using enumeration, ensuring compile-time type safety.