int FAO::GetPrecedence()
{
if (cur_token_.GetType() == TokenType::TOKEN_OPERATION){
return this->binary_op_precedence_[cur_token_.GetOperation()];
}
return -1;
}
ExprAST * FAO::ParseBinOpRHS(int Expc, ExprAST * lhs)
{
// If this is a binary operator,find its precedence
while (true){
int TokPrec = GetPrecedence();
// If this is a binary operator,find its precedence at least as tightly as the current binary operator
// consume it,otherwise we are done.
if (TokPrec < Expc){
return lhs;
}
// Okay,we know this is binary operator
char BinOp = cur_token_.GetOperation();
Advance(); // eat binary operator
// Parse the primary expression after the binary operator
ExprAST * rhs = ParsePrimary();
if (rhs == nullptr){
return nullptr;
}
// If binary operator less tightly with rhs than the operator after rhs,let
// the pending operator than rhs as its lhs
int NextPrec = GetPrecedence();
if (TokPrec < NextPrec){
rhs = ParseBinOpRHS(TokPrec + 1, rhs);
if (rhs == nullptr){
return nullptr;
}
}
// Merge lhs/rhs
lhs = new BinaryOpExpr(BinOp, lhs, rhs);
}
return lhs;
}