foldLeft.io

List foldLeft := method(
  context := Object clone prependProto(call sender)

  if(call sender hasLocalSlot("self"),
    context setSlot("self", call sender self)
  )

  initValue := call message evalArg(0)
  eName := call message argAt(1) name
  eResult := call message argAt(2) name
  body := call message argAt(3)

  context setSlot(eResult, initValue)
  self foreach(value,
    context setSlot(eName, getSlot("value"))
    context setSlot(eResult, context doMessage(body))
  )

  context getSlot(eResult)
)

List myAverage := method(
  total := self foldLeft(0, e, r,
    if(e isKindOf(Number),
       e + r,
       Exception raise("Value is not a number.")
    )
  )
  total / self size
)

list(1,2,3) myAverage println
list(1,"2",3) myAverage println