Calculator Documentation

Step 5

This is step 5 of the calculator project in Exploration 68 of Exploring C++: The Programmer's Introduction to C++.

This version of the calculator adds library files. The save command saves the global symbol table to a file, and the load command loads symbols from a file into the global symbol table.

This calculator has a simple syntax:

   start ::= statement-list
   statement-list ::= empty | statement-list statement
   statement ::= definition | quit | expression | "load" string | "save" string
   definition ::= "def" identifier optional-parameters "=" expression
   optional-parameters ::= empty | "(" optional-identifier-list ")"
   optional-identifier-list ::= empty | identifier-list
   identifier-list ::= identifier | identifier-list "," identifier
   expression ::= multiplicative-expression "+" multiplicative-expression |
                  multiplicative-expression "-" multiplicative-expression
   multiplicative-expression ::= unary-expression "*" unary-expression |
                                 unary-expression "/" unary-expression
   unary-expression ::= "-" primary | "+" primary | primary
   primary ::= number | function-call | "(" expression ")"
   function-call ::= identifier optional_arguments
   optional_arguments ::= empty | "(" optional-expression-list ")"
   optional-expression-list ::= empty | expression-list
   expression-list ::= expression | expression-list "," expression
   

Function arguments are evaluated lazily. There are no variables, only functions, but function definitions can look just like variable assignments:

   def pi = 3.141592653589792
   

so there really isn't any difference between a variable and a function.

The calculator reads expressions from the standard input, evaluates them, and prints the results to the standard output. It's that simple.

The calculator parses expression into a parse tree. The parser uses node objects. The node class uses the pimpl idiom with a tree of node_impl-derived classes.

---