Token.cpp

//
// Created by martin on 30/12/2021.
//

#include "../std_lib_facilities.h"
#include "Token.h"


class Token
{
 public:
  char kind;        // what kind of token
  double value;     // for numbers: a value
  Token (char ch)    // make a Token from a char
	  : kind(ch), value(0)
  {}
  Token (char ch, double val)     // make a Token from a char and a double
	  : kind(ch), value(val)
  {}
};

//------------------------------------------------------------------------------

class Token_stream
{
 public:
  Token_stream ();   // make a Token_stream that reads from cin
  Token get ();      // get a Token (get() is defined elsewhere)
  void putback (Token t);    // put a Token back
 private:
  bool full;        // is there a Token in the buffer?
  Token buffer;     // here is where we keep a Token put back using putback()
};

//------------------------------------------------------------------------------

// The constructor just sets full to indicate that the buffer is empty:
Token_stream::Token_stream ()
	: full(false), buffer(0)    // no Token in buffer
{
}

//------------------------------------------------------------------------------

// The putback() member function puts its argument back into the Token_stream's buffer:
void Token_stream::putback (Token t)
{
  if (full)
  {
	error("putback() into a full buffer");
  }
  buffer = t;       // copy t to buffer
  full = true;      // buffer is now full
}

//------------------------------------------------------------------------------

Token Token_stream::get ()
{
  if (full)
  {       // do we already have a Token ready?
	// remove token from buffer
	full = false;
	return buffer;
  }

  char ch;
  cin >> ch;    // note that >> skips whitespace (space, newline, tab, etc.)

  switch (ch)
  {
  case ';':    // for "print"
  case 'q':    // for "quit"
  case '(':
  case ')':
  case '+':
  case '-':
  case '*':
  case '/':
	return {ch};        // let each character represent itself
  case '.':
  case '0':
  case '1':
  case '2':
  case '3':
  case '4':
  case '5':
  case '6':
  case '7':
  case '9':
  {
	cin.putback(ch);         // put digit back into the input stream
	double val;
	cin >> val;              // read a floating-point number
	return {'8', val};   // let '8' represent "a number"
  }
  default:
	error("Bad token");
  }
}