Spice distinguishes strictly between functions and procedures. Functions are used to calculate something from a given input. Other than procedures, functions must have a return value. The paradigma here is, that a function calculates and returns something whereas a procedure executes some action.

Functions in Spice can be defined like this:

f<double> functionName() {
    ... // Do something
    return 5.6; // Return some value anywhere in the function body

Spice also allows you to pass parameters to a function. This parameters may also have default values, which can then be omitted when calling the function.


Parameters with default value / optional parameters have to go after those without default value in the function declaration.

Here, the second parameter is one with a default value attached.

f<int> demoFunction(string parameter1, double parameter2 = 5.89) {
    ... // Do something with the parameters
    result = -4;

Theis procedure could get called like so:

demoFunction("another input", 1.0);


If you only want to execute some actions and don't need to return a value to the caller, please consider to use procedures instead of functions.