{ =f =a a len =l
  l {
    0 a *
    1 l 1 sub range { a * f * } each
    } { "fold on empty array" die }
  ? *
} /fold deff

{ =f _ len =l l dearray l 1 sub f rep } /foldshort deff

{ =f { f fold } } /enfold deff

[ 1 2 3 ]
_ |add fold dump
_ |add foldshort dump
_ |add enfold * dump
-