code: func All(f, xs interface{}) bool {
  	chk := ty.Check(
  		new(func(func(ty.A) bool, []ty.A) bool),
  		f, xs)
  	vf, vxs := chk.Args[0], chk.Args[1]
  
  	xsLen := vxs.Len()
  	for i := 0; i < xsLen; i++ {
  		if !call1(vf, vxs.Index(i)).Interface().(bool) {
  			return false
  		}
  	}
  	return true
  }
docs: // All has a parametric type:
  //
  //	func All(p func(A) bool, xs []A) bool
  //
  // All returns `true` if and only if every element in `xs` satisfies `p`.