Some gems in there First, we have to realise that many array (or other collection) operations like map, filter and reverse can be defined in terms of a reduce.

Some gems in there First, we have to realise that many array (or other collection) operations like map, filter and reverse can be defined in terms of a reduce. ... To get at the reducing functions, we need to make map and filter more generic by extracting the pieces they have in common: - Use of collection.reduce - The 'seed' value is an empty array - The concat operation performed on result and the input (transform-ed or not) ... Before we do that, we need a new function: identity. It simply returns whatever it is given: (Although there is a lot that may be obvious to the Haskell guys)