The `MonoArrayFn` functor

The `MonoArrayFn` functor allows easy construction of new monomorphic array structures.

## Synopsis

``functor MonoArrayFn (type elem) :> MONO_ARRAY where type elem = elem``

## Description

This functor takes an element type and defines a structure that matches the `MONO_ARRAY` signature from the SML Basis Library, which can then be supplied to other functors that require such an argument.