// convert2postfix converts an infix expression to postfix
func convert2postfix(tokens []string) []string {
var stack stack.Stack
var result []string
for _, token := range tokens {
if isOperator(token) {
OPERATOR:
for {
top, err := stack.Top()
if err == nil && top != "(" {
if opGTE(top.(string), token) {
pop, _ := stack.Pop()
result = append(result, pop.(string))
} else {
break OPERATOR
}
}
break OPERATOR
}
stack.Push(token)
} else if token == "(" {
stack.Push(token)
} else if token == ")" {
PAREN:
for {
top, err := stack.Top()
if err == nil && top != "(" {
pop, _ := stack.Pop()
result = append(result, pop.(string))
} else {
stack.Pop() // pop off "("
break PAREN
}
}
} else if isOperand(token) {
result = append(result, token)
}
}
for !stack.IsEmpty() {
pop, _ := stack.Pop()
result = append(result, pop.(string))
}
return result
}
