PCL: Add some semantically erroroneous programs

[souvlakias]

Adds a few more semantically erroneous programs that are grammatically correct. Follows the structure and naming of other examples (semantic_error_<i>.pcl)

Coverage

Labels:

• Illegal cross scope goto
• goto to a declared but undefined label

Functions & Procedures:

• Usage of result keyword in non-function blocks
• Inconsistency between forward and actual header declarations
• Assignment from a procedure call
• Passing a constant or expression to a var argument (l-value expected)

Misc:

• Dereference of nil

[souvlakias]

Usage of result keyword in non-function blocks

This I'm not so sure about since some lexical erroneous programs (e.g.) do use it, but are just marked as lexical errors.
It's not formally defined in the pdf, but I think what makes sense is that it should only exist in functions' main blocks. So, If you want, I can change/fix the lexical erroneous examples to not have this semantic error

[kostis]

This I'm not so sure about since some lexical erroneous programs (e.g.) do use it, but are just marked as lexical errors.

It's a bit unclear what you are concerned about. The program you mention is lexically erroneous because it contains a stray $ character, so it should be rejected early by the lexer, and never reach the semantic analysis pass of a (correct) PCL compiler. So, whether the result keyword is used correctly or not in that program is irrelevant (a non-issue).

If I have misunderstood your concern, feel free to comment again.

[souvlakias]

So, whether the result keyword is used correctly or not in that program is irrelevant (a non-issue).

Yes, you are right. All good then, sorry for the confusion 😅

[kostis]

Thanks for your contribution. I am merging this.