generates AST for operators like +, -...
firstOperand is the first operand for the operator. index is the index of the token which is the operator
changes index to the index of the token after the last token related to the operator
See Implementation
generates AST for operators like +, -...
firstOperand is the first operand for the operator. index is the index of the token which is the operator
changes index to the index of the token after the last token related to the operator