gistfile1.scala

/** I think it's better if we can define replaceFirst generally on Iterables */
def replaceFirst[T](it: Iterable[T], predicate:T=>Boolean, f:T=>T): Iterable[T] = {
  if (it.isEmpty) it
  else if (predicate(it.head)) it.take(1) .map(f) ++ it.tail
  else it.take(1) ++ replaceFirst(it.tail, predicate, f)
}

/** 
 * Otherwise on Lists, that can be fun to use a foldLeft.
 * It's a bit ugly though with the trailing _2 
 */	
def alwaysTrue[T] = (t: T) => true
def replaceFirst2[T](it: List[T], predicate:T=>Boolean, f:T=>T): List[T] = {
  it.foldLeft((predicate, List[T]())) { case ((p, res), current) => 
    if (p(current))
     (alwaysTrue, f(current) :: res)
    else
     (predicate, current :: res)
  }._2
}