src/Calculator.cpp

   1 /*******************************************************************************
   2  * Reverse Polish Notation calculator.                                         *
   3  * Copyright (c) 2007-2008, Samuel Fredrickson <kinghajj@gmail.com>            *
   4  * All rights reserved.                                                        *
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  24  * DAMAGE.                                                                     *
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  26
  27 /*******************************************************************************
  28  * Calculator.cpp - non-command Calculator methods.                            *
  29  ******************************************************************************/
  30
  31 #include "rpn.h"
  32 #include <boost/tokenizer.hpp>
  33 #include <sstream>
  34 using namespace boost;
  35 using namespace std;
  36 using namespace RPN;
  37
  38 void Calculator::Eval(string s)
  39 {
  40     typedef tokenizer< char_separator<char> > Tokens;
  41     char_separator<char> sep(" \t\n");
  42     Tokens tokens(s, sep);
  43
  44     if(!HasStack()) return;
  45
  46     for(Tokens::iterator tok = tokens.begin();
  47         tok != tokens.end() && status == Continue;
  48         ++tok)
  49     {
  50         Commands::iterator  foundCommand   = commands.find(*tok);
  51         Operators::iterator foundOperator  = operators.find(*tok);
  52         Variables::iterator foundVariable  = variables.find(*tok);
  53         Value val;
  54
  55         // if the token is a number, push it.
  56         if(istringstream(*tok) >> val)
  57             CurrentStack().push_front(val);
  58
  59         // if the token is a command, perform it.
  60         else if(foundCommand != commands.end())
  61         {
  62             const Command& command = foundCommand->second;
  63             vector<string> args;
  64             args.reserve(command.NumArgs());
  65
  66             // collect a list of tokens that will be the arguments to the
  67             // command.
  68             while(tok != tokens.end() && args.size() != command.NumArgs())
  69                 args.push_back(*++tok);
  70
  71             // only perform a command if we can give it enough arguments.
  72             if(args.size() == command.NumArgs())
  73                 command.Perform(*this, args);
  74         }
  75
  76         // if the token is an operator and that stack has at least two items,
  77         // then perform that operator.
  78         else if(foundOperator != operators.end() && StackSize() > 1)
  79         {
  80             Value b = TopmostItem(); CurrentStack().pop_front();
  81             Value a = TopmostItem(); CurrentStack().pop_front();
  82             CurrentStack().push_front(foundOperator->second(a, b));
  83         }
  84
  85         // if the token is a variable, push the variable onto the stack.
  86         else if(foundVariable != variables.end())
  87             CurrentStack().push_front(foundVariable->second);
  88
  89         // otherwise, if the stack has at least one item, set a new variable
  90         // whose name is the token and value is the top item.
  91         else variables[*tok] = TopmostItem();
  92     }
  93 }
  94
  95 // displays the top item of the stack if there is one.
  96 // I tried to write this as a friend operator<<(), but I got errors for
  97 // accessing private data, which is what friend functions are supposed to be
  98 // able to do!
  99 void Calculator::Display() const
 100 {
 101     Print(TopmostItem());
 102 }