The checking of the AST currently happens through running the generated code. This is obviously a bad idea.

We should implement a check phase after parsing the AST. For now, the following checks should be in place:

• Check, if an accessed symbol is defined in the scope
• Check, if types are compatible (function parameters should have the correct type, let x: int = "Hello" is invalid, etc.)

Room for discussion

• Should this be done while parsing the tree instead?
• Should this be one large check, or modular checkers that run sequentially?