型推論ネタ, 以下Aは動くがBはmapに呪いが掛かってしぬ

// A
let s = sequence(first:0){$0+1}
.lazy
.map{$0*2}
s.prefix(10)
.reversed()
.forEach{print($0)}

// B
sequence(first:0){$0+1}
.lazy
.map{$0*2}
.prefix(10)
.reversed()
.forEach{print($0)}