public object VisitBinary(Expression.Binary expression)
{
var left = Evaluate(expression.Left);
var right = Evaluate(expression.Right);
switch (expression.Operator.Type)
{
case TokenType.Minus:
CheckNumberOperands(expression.Operator, left, right);
return((double)left - (double)right);
case TokenType.Slash:
CheckNumberOperands(expression.Operator, left, right);
return((double)left / (double)right);
case TokenType.Star:
CheckNumberOperands(expression.Operator, left, right);
return((double)left * (double)right);
case TokenType.Plus:
if (left is double && right is double)
{
return((double)left + (double)right);
}
if (left is string && right is string)
{
return((string)left + (string)right);
}
throw new RuntimeError(expression.Operator, "Operands must be two numbers or two strings.");
case TokenType.Greater:
CheckNumberOperands(expression.Operator, left, right);
return((double)left > (double)right);
case TokenType.GreaterEqual:
CheckNumberOperands(expression.Operator, left, right);
return((double)left >= (double)right);
case TokenType.Less:
CheckNumberOperands(expression.Operator, left, right);
return((double)left < (double)right);
case TokenType.LessEqual:
CheckNumberOperands(expression.Operator, left, right);
return((double)left <= (double)right);
case TokenType.BangEqual:
return(!IsEqual(left, right));
case TokenType.EqualEqual:
return(IsEqual(left, right));
default:
throw new NotImplementedException();
}
}
private Expression Multiplication()
{
var expression = Unary();
while (Match(TokenType.Star, TokenType.Slash))
{
var @operator = Previous();
var right = Unary();
expression = new Expression.Binary(expression, @operator, right);
}
return(expression);
}
private Expression Addition()
{
var expression = Multiplication();
while (Match(TokenType.Minus, TokenType.Plus))
{
var @operator = Previous();
var right = Multiplication();
expression = new Expression.Binary(expression, @operator, right);
}
return(expression);
}
private Expression Comparison()
{
var expression = Addition();
while (Match(TokenType.Greater, TokenType.GreaterEqual, TokenType.Less, TokenType.LessEqual))
{
var @operator = Previous();
var right = Addition();
expression = new Expression.Binary(expression, @operator, right);
}
return(expression);
}
private Expression Equality()
{
var expression = Comparison();
while (Match(TokenType.BangEqual, TokenType.EqualEqual))
{
var @operator = Previous();
var right = Comparison();
expression = new Expression.Binary(expression, @operator, right);
}
return(expression);
}
public string VisitBinary(Expression.Binary expression)
{
return(Parenthesize(expression.Operator.Lexeme, expression.Left, expression.Right));
}
