statements.swift

import Foundation  
protocol Term {  
  var value: String { get }  
}  
extension Term  {}  
struct Statement  {  
  var terms: [Term] = []  
  mutating func addItem(term: Term) {  
    terms.append(term)  
  }  
}  
struct Fraction: Term {  
  let numerator: Statement  
  let denominator: Statement  
  let value: String  
}  
struct Exponent: Term {  
  let base: String  
  let power: Statement  
  let value: String  
}  
struct Variable: Term {  
  let value: String  
}  
struct Operator: Term {  
  let value: String  
}  
struct Number: Term {  
  let value: String  
}  
  
  
func highlightTerm(term:Term) {  
    for(_, localTerm) in EnumerateSequence(statement.terms) {  
          //how can I check if  
          //term == localTerm?  
    }  
  } 
  
  
protocol Equatable {
   func ==(lhs: Self, rhs: Self) -> Bool
}
extension Term: Equatable { }
func ==(lhs: Term, rhs: Term) -> Bool {
  return lhs.value == rhs.value
}