result can't be used in expressions when not initialized

Bug description

Using result in an expression leads to a runtime error during interpretation. For example, the following code produces an error during the evaluation of the if's condition:

class A {

    def boolean isX() {
        if (result) {

        }
        result := false;
    }

}

The error is "Couldn't find the 'result' variable".

Expected behavior

Not sure. One of the following:

result is set a default value,
it is explicitely forbidden to use result without initializing it first and this is enforced by an error marker in the editor.

How to reproduce

Steps to reproduce the behavior:

Create an ALE project
Write a semantics that uses result in an expression as shown above
Run the interpreter

Additional context

ALE version: master @ a1a0bf8

Issue caused by the following line:

https://github.com/gemoc/ale-lang/blob/a1a0bf83da3c2228b127d4dc73e3bf733f1b9b9e/plugins/org.eclipse.emf.ecoretools.ale.core/src/org/eclipse/emf/ecoretools/ale/core/interpreter/internal/MethodEvaluator.java#L688

Since result has not been initialized yet, the map returned by scopes.getCurrent().getVariableValues() won't contain it. The appropriate fix depends on the chosen solution.

gemoc / ale-lang