Alright, let's write a comment about the actual implementation described in the post. So: why make the symbol table a linked list that has its head fixed at "ma

Alright, let's write a comment about the actual implementation described in the post. So: why make the symbol table a linked list that has its head fixed at "main" and grows and shrinks at its tail? It is used in a stack-like fashion, so why not reverse the order: put "main" at its tail and grow and shrink it at its head? That simplifies adding symbols: you keep checking for duplicates until the depth of the symbols you see drops below your depth, and actual insertion doesn't need the pointer to the list's last element, you insert at the head. That simplifies destroying symbols: you keep popping the head until you meet a TOK_PROCEDURE at which point you stop. That simplifies looking symbols up: you search until the first name match and return it immediately, instead of remembering the last seen matching symbol while traversing the full list. I am not even talking about efficiency (although of course this implementation is also more efficient in all 3 use cases), it's about code simplicity: the less context you need to maintain during a list traversal, the easier it is to understand what this traversal looks for.