SwiftのREPLのメモ ref: http://qiita.com/tikidunponpon/items/66e459b0bee83eb2e103

file0.swift

  1> "100".toInt()
$R0: Int? = 100
  2> var a = 250
a: Int = 250
  3> func sum(val1:Int, val2:Int)->Int{
  4.     return val1 + val2
  5. }
  6>
  7> sum(10, 20)
$R1: Int = 30
  8> let result = sum($R0, a)
repl.swift:8:18: error: value of optional type 'Int?' not unwrapped; did you mean to use '!' or '?'?
let result = sum($R0, a)
                 ^
                    !
  8> let result = sum($R0!, a)
  9.
result: Int = 350
  9> result = 500
repl.swift:9:8: error: cannot assign to 'let' value 'result'
result = 500