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By definition a Functor is simply a first class method, but these are quite
common in Ruby with the Method, UnboundMethod and Proc classes. So for
Ruby we define a Functor as a Higher Order Function. Essentially, a functor
can vary its behavior according to the operation applied to it. Consider the
following simplistic example.
f = Functor.new { |op, x| x.send(op, x) }
f + 1 #=> 2
f + 2 #=> 4
f + 3 #=> 6
f * 1 #=> 1
f * 2 #=> 4
f * 3 #=> 9
Notice that the constructor takes a block, the first argument of which is always the method operating on the functor. All subsequent arguments are optional dependent upon the use case.
We can also think of the Functor as an anonymous/generic delegator. Instead of having to create a specialized delegator class, a functor can be used instead. Functors are perfect when the delegation required is minimal.
NOTE Ruby functors are not the same as Haskell functors. In Ruby Enumerators are more akin to Haskell's idea of a functor.
In addition to the Functor class, this library includes a dozen or so useful core extensions that take advantage of the power of the functor. Have a look at the demo directory for a rundown on the methods available and how they work.
Copyright (c) 2004 Rubyworks
Functor is distributable in accordance with the BSD-2-Clause license.
See LICENSE.txt for details.