test uniqueness of labels

See merge request !7

Make sure that the labels are unique between multiple
expressions/statements as well as between different kinds.

Testing Runtime Errors

See merge request !6

This reverts commit c9bc86ee.

Edge cases for dead code analysis

See merge request !3

adding some type checking tests

See merge request !5

this was necessary to generate correct syntax errors, specifically
regarding the line number

ref #1