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;
}
PNode CreateInfixTree(char* exp)
{
// create a dummy root with minimal precedence
// its content is trivial
PNode root = CreateNode("0");
root->precedence = 0;
// the previous operand of current operator
PNode preOperand = NULL;
// the previous operator of current operator
PNode preOperator = root;
// the impact of preceding parenthesis, if any
int correction = 0;
int i = 0;
char* token = strtok( exp, " " );
while(token)
{
if (IsOperand(token))
{
preOperand = CreateNode(token);
}
else if (IsOperator(token))
{
printf("entrou em eh operador\n");
PNode p = CreateNode(token);
p->precedence = GetPrecedence(token) + correction;
if (p->precedence > preOperator->precedence)
{
p->left = preOperand;
preOperator->right = p;
p->parent = preOperator;
}
else
{
preOperator->right = preOperand;
PNode q = preOperator->parent;
while (p->precedence <= q->precedence) q = q->parent;
p->left = q->right;
q->right = p;
p->parent = q;
}
preOperand = NULL;
preOperator = p;
}//else if (IsOperator(exp[i])
else if (IsLeftParenthesis(token))
{
correction += 2;
}
else if (IsRightParenthesis(token))
{
correction -= 2;
}
else
{
printf("illegal token found: %c\n", exp[i]);
break;
}
token = strtok(NULL, " ");
}//while
if (preOperand == NULL)
printf("illegal expression: cannot end with operator: %s\n", preOperator->data);
else preOperator->right = preOperand;
// delete dummy root
PNode realRoot = root->right;
//delete root;
free(root);
if (realRoot) realRoot->parent = NULL;
return realRoot;
}
