private Expr Multiplication()
{
Expr expr = Unary();
while (Match(TokenType.SLASH, TokenType.STAR))
{
Token oper = Previous();
Expr right = Unary();
expr = new Expr.Binary(expr, oper, right);
}
return(expr);
}
private Expr Addition()
{
Expr expr = Multiplication();
while (Match(TokenType.MINUS, TokenType.PLUS))
{
Token oper = Previous();
Expr right = Multiplication();
expr = new Expr.Binary(expr, oper, right);
}
return(expr);
}
private Expr Comparison()
{
Expr expr = Addition();
while (Match(TokenType.GREATER, TokenType.GREATER_EQUAL, TokenType.LESS, TokenType.LESS_EQUAL))
{
Token oper = Previous();
Expr right = Addition();
expr = new Expr.Binary(expr, oper, right);
}
return(expr);
}
private Expr Equality()
{
Expr expr = Comparison();
while (Match(TokenType.BANG_EQUAL, TokenType.EQUAL_EQUAL))
{
Token oper = Previous();
Expr right = Comparison();
expr = new Expr.Binary(expr, oper, right);
}
return(expr);
}
public Void VisitBinaryExpr(Expr.Binary expr)
{
Resolve(expr.left);
Resolve(expr.right);
return(null);
}
public object VisitBinaryExpr(Expr.Binary expr)
{
object left = Evaluate(expr.left);
object right = Evaluate(expr.right);
switch (expr.oper.Type)
{
case TokenType.PLUS:
if (left is int && right is int)
{
return((int)left + (int)right);
}
if (left is float && right is float)
{
return((float)left + (float)right);
}
if (left is string && right is string)
{
return((string)left + (string)right);
}
throw new RuntimeError(expr.oper, "Operands must be two numbers or two strings.");
case TokenType.GREATER:
CheckNumberOperands(expr.oper, left, right);
return((float)left > (float)right);
case TokenType.GREATER_EQUAL:
CheckNumberOperands(expr.oper, left, right);
return((float)left >= (float)right);
case TokenType.LESS:
CheckNumberOperands(expr.oper, left, right);
return((float)left < (float)right);
case TokenType.LESS_EQUAL:
CheckNumberOperands(expr.oper, left, right);
return((float)left <= (float)right);
case TokenType.BANG_EQUAL: return(!IsEqual(left, right));
case TokenType.EQUAL_EQUAL: return(IsEqual(left, right));
case TokenType.MINUS:
CheckNumberOperands(expr.oper, left, right);
return((float)left - (float)right);
case TokenType.STAR:
CheckNumberOperands(expr.oper, left, right);
return((float)left * (float)right);
case TokenType.SLASH:
CheckNumberOperands(expr.oper, left, right);
return((float)left / (float)right);
}
// Unreachable.
return(null);
}
