Creating and populating symbol tables for each scope

A symbol table contains a record of all the names that are declared for a scope. There is one symbol table for each scope. A symbol table provides a means of looking up symbols by their name to obtain information about them. If a variable was declared, the symbol table lookup returns a record with all the information known about that symbol: where it was declared, what its data type is, whether it is public or private, and so on. All this information can be found in the syntax tree. If we also place it in a table, the goal is to access the information directly, from anywhere else that information is needed.

The traditional implementation of a symbol table is a hash table, which provides a very fast information lookup. Your compiler could use any data structure that allows you to store or retrieve information associated with a symbol, even a linked list. But hash tables are the best for this, and they are standard in Unicon and...