Meaning of: feature was simple feature call but got receiver instead of null

Question

I implemented my own XbaseInterpreter. I forked the context in my subclass and added some new values. Lets say one of the values has type X.
When I call the evaluate method with my XBlockExpression and the forked context I get the exception
"feature was simple feature call but got receiver instead of null. Receiver: <here the instance of X>
What am I doing wrong?
What does the exception message mean?

Answer 1

Hi Sebastian,
I understand the first part of your answer. In my case the Xbase interpreter tries to assign an object to a variable where the interpreter thinks the left side of the equation is void which leads to the given message "feature was simple feature..."
But I do not understand how this can happen in my case.
I have an XBlockExpression with this content:
val x = 1
return x == 1
The error occurs for the variable declaration when the interpreter tries to assign the integer to the left side.
What am I missing?
Do I have to initialize the evaluation context?
The strange thing is that if I start the interpreter by initializing it with the standalone setup within Eclipse (which is not recommended) I do not get the above mention exception at all ( I do get class cast exceptions because of including the standalone setup but the expression is interpreted correctly).
What is the difference between the standalone setup and the "normal" Eclipse runimte for interpreting expressions?
With regards,
Udo