Part three of a small series explaining Fuzion using idioms from https://www.programming-idioms.org/.
Fuzion idiom #3, Create a procedure:
A procedure in Fuzion is a feature with effects.
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The feature declared here is called `finish`. It has one argument `name` of type `String`. The arrow `=>` says that this feature is a function and the result type is inferred automatically from the code.
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To call this feature, it is sufficient to write the name followed by an argument of type `String`, here we call `finish "schöne Welt!"`:
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The code of `finish` performs a call to `say`, which prints a given string and returns a value of type `unit`, which in Fuzion has a similar role like `void` in Java or C, but it is a proper first-class type. So the inferred result type of `finish` is `unit` as well.
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Fuzion uses effects, which means that `say` does not just print the string, but it uses the `io.out` effect from the current environment. The default `io.out` prints that string to `stdout`, but we could replace it by an effect that does something else.
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The effects that are required by a feature can be determined by static analysis. Analysing our example for effects (by selecting `Effects!`) results in `io.out`:
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For library features, the effects must be explicit. In our example, if we would want to place it in a library, we must hence add `! io.out` after the type signature to document the use of this effect, otherwise building that library module would result in an error:
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More on the Fuzion language, more examples, idioms, a tutorial, design background can be found at https://flang.dev
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