Initial API definition and a simple property. This article is one of a series on finding properties for a budgeting kata. I expect you to have read the previous articles in the series. In this article we get started by adding a first sketch of data structures and an initial, simple property. The code is available on GitHub, in the commit 1f7aceb. Budget type # My intent with the entire exercise is to follow a variation of test-driven development (TDD) that uses QuickCheck properties rather than static examples. Even so, Haskell is such a strongly typed language that I often...