Semantic analysis
The semantic analyzer walks the AST and checks for various semantic rules of the language; for example, a variable must be declared before use or types of variables must be compatible in an expression. The semantic analyzer can also print out warnings if it finds a situation that can be improved. For the example expression language, the sematic analyzer must check that each used variable is declared, because that is what the language requires. A possible extension (which will not be implemented here) is to print a warning message if a declared variable is not used.
The semantic analyzer is implemented in the Sema class, and semantic analysis is performed by the semantic() method. Here is the complete Sema.h header file:
#ifndef SEMA_H
#define SEMA_H
#include "AST.h"
#include "Lexer.h"
class Sema {
public:
  bool semantic(AST *Tree);
};
#endif
The implementation is in the Sema.cpp file. The interesting part is the semantic analysis...
