use FP::PureArray; use FP::Div 'inc'; is purearray(1,4,5)->map(*inc)->sum, 13;
Perl arrays blessed into the `FP::PureArray` package, inheriting from `FP::Abstract::Pure`, and coming with the functions from `FP::Array` as methods.
If you hand someone an FP::PureArray you guarantee that you won't mutate it. This might be enforced in the future by making them immutable (todo).
Write alternative implementation that is efficient for updates on big arrays.