scalaで連続な差分

var tmp=a(0);a.map{b=>var c=b-tmp;tmp=b;c}.slice(1,a.length)

こんな感じ

scala> a
res18: Array[Int] = Array(1, 2, 3, 4, 7)

scala> tmp=a(0);a.map{b=>var c=b-tmp;tmp=b;c}.slice(1,a.length)
tmp: Int = 7
res19: Array[Int] = Array(1, 1, 1, 3)