Errors in Modelica

In Modelica, error handling is typically done through exceptions rather than explicit error return values. However, we can simulate a similar approach using optional return types and dedicated error classes. Here’s how we might structure error handling in Modelica:

model ErrorHandling
  import Modelica.Utilities.Streams.*;

  class Error
    String message;
  end Error;

  class OutOfTeaError
    extends Error(message="no more tea available");
  end OutOfTeaError;

  class PowerError
    extends Error(message="can't boil water");
  end PowerError;

  function f
    input Integer arg;
    output Integer result;
    output Error error;
  algorithm
    if arg == 42 then
      result := -1;
      error := Error(message="can't work with 42");
    else
      result := arg + 3;
      error := Error(message="");
    end if;
  end f;

  function makeTea
    input Integer arg;
    output Error error;
  algorithm
    if arg == 2 then
      error := OutOfTeaError();
    elseif arg == 4 then
      error := PowerError();
    else
      error := Error(message="");
    end if;
  end makeTea;

algorithm
  for i in {7, 42} loop
    (result, error) := f(i);
    if error.message <> "" then
      print("f failed: " + error.message + "\n");
    else
      print("f worked: " + String(result) + "\n");
    end if;
  end for;

  for i in 1:5 loop
    error := makeTea(i);
    if error.message <> "" then
      if error.message == "no more tea available" then
        print("We should buy new tea!\n");
      elseif error.message == "can't boil water" then
        print("Now it is dark.\n");
      else
        print("unknown error: " + error.message + "\n");
      end if;
    else
      print("Tea is ready!\n");
    end if;
  end for;
end ErrorHandling;

In this Modelica implementation:

We define a base Error class and specific error types (OutOfTeaError and PowerError) to represent different error conditions.
Functions return both a result and an error. An empty error message indicates no error occurred.
The f function demonstrates returning different results based on the input, including an error for a specific case.
The makeTea function shows how to return different types of errors based on the input.
In the main algorithm, we demonstrate how to check for errors and handle them appropriately.
Instead of using errors.Is, we compare error messages directly. In a more robust implementation, you might want to use inheritance or a type system to differentiate between error types.
The print function is used for console output, as Modelica doesn’t have a direct equivalent to fmt.Println.

This approach simulates error handling in a way that’s somewhat similar to the original Go code, while adapting to Modelica’s language features and conventions. Note that error handling in Modelica is typically done through exceptions, and this example is more for illustrative purposes to show how one might implement a similar pattern to Go’s error handling.

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Errors in Modelica