/// G. Hagopian PPP chapter 6 ex 7

/**
 * Write a grammar for bitwise logical expressions.
 * A bitwise logical expression is much like an
 * arithmetic expression except that the operators
 * are ! (not), ~ (complement), & (and), | (or),
 * and ^ (exclusive or). Each operator does its
 * operation to each bit of its integer operands
 * (see §25.5). ! and ~ are prefix unary operators.
 * A ^ binds tighter than a | (just as * binds
 * tighter than +) so that x|y^z means x|(y^z)
 * rather than (x|y)^z. The & operator binds
 * tighter than ^ so that x^y&z means x^(y&z).

Grammar:

Expression
    xterm  or
    Expression | xterm
xterm
    aterm   or
    xterm ^ aterm
aterm
    primary
    aterm & primary
primary
    bitset
    ("expression")
**/


#include "std_lib_facilities.h"
#include <bitset>
//------------------------------------------------------------------------------

const unsigned nbits = 32;

class Token {
public:
    char kind;        // what kind of token
    bitset<nbits> value;     // for numbers: a value
    Token(char ch)    // make a Token from a char
        :kind(ch), value(0) { }
    Token(char ch, bitset<nbits> 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 '{': case '}':
        return Token(ch);        // let each character represent itself
    case '.':
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
    {
        cin.putback(ch);         // put digit back into the input stream
        unsigned val;
        cin >> val;              // read a floating-point number
        bitset<nbits> bits = val;
        return Token('8',bits);   // let '8' represent "a number"
    }
    default:
        error("Bad token");
    }
}

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

Token_stream ts;  /// provides get() and putback()

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

bitset<nbits> expression();    // declaration so that primary() can call expression()

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

/// deal with numbers and parentheses
bitset<nbits> primary()
{
    Token t = ts.get();
    switch (t.kind) {
    case '(':    // handle '(' expression ')'
    {
        bitset<nbits> d = expression();
        t = ts.get();
        if (t.kind != ')') error("')' expected");
        return d;
    }
    case '{':    // handle '(' expression ')'
    {
        bitset<nbits> d = expression();
        t = ts.get();
        if (t.kind != '}') error("')' expected");
        return d;
    }
    case '8':
    {         // we use '8' to represent a number
        return t.value;  // return the number's value
    }
    default:
        error("primary expected");
    }
}

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

bitset<nbits> aterm();

/// deal with ^
bitset<nbits> xterm()
{
    bitset<nbits> left = aterm();
    Token t = ts.get();        // get the next token from token stream

    while(true) {
        switch (t.kind) {
        case '^':
            left ^= aterm();
            t = ts.get();
            break;
        default:
            ts.putback(t);     // put t back into the token stream
            return left;
        }
    }
}

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

/// deal with *, /, and %
bitset<nbits> aterm()
{
    bitset<nbits> left = primary();
    Token t = ts.get();        // get the next token from token stream

    while(true) {
        switch (t.kind) {
        case '&':
            left &= primary();
            t = ts.get();
            break;
        default:
            ts.putback(t);     // put t back into the token stream
            return left;
        }
    }
}
//------------------------------------------------------------------------------

// deal with + and -
bitset<nbits> expression()
{
    bitset<nbits> left = xterm();      // read and evaluate a Term
    Token t = ts.get();        // get the next token from token stream

    while(true) {
        switch(t.kind) {
        case '|':
            left |= xterm();    // evaluate Term and add
            t = ts.get();
            break;
        default:
            ts.putback(t);     // put t back into the token stream
            return left;       // finally: no more + or -: return the answer
        }
    }
}

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

int main()
try
{
    bitset<nbits> val{0};
    while (cin) {
        Token t = ts.get();

        if (t.kind == 'q') break; // 'q' for quit
        if (t.kind == ';')        // ';' for "print now"
            cout << "=" << val << '\n';
        else
            ts.putback(t);
        val = expression();
    }
}
catch (exception& e) {
    cerr << "error: " << e.what() << '\n';
	keep_window_open();
    return 1;
}
catch (...) {
    cerr << "Oops: unknown exception!\n";
	keep_window_open();
    return 2;
}