Get Programming with F#

Lesson 18. Folding your way to success

The preceding few lessons covered the main collection types and how to use them. Here we’ll round off with a few scenarios describing how collections can be used in interesting ways to achieve outputs and transformations that you might not think possible through folding. You’ll look at

• Understanding aggregations and accumulation
• Avoiding mutation through fold
• Building rules engines and functional chains

18.1. Understanding aggregations and accumulators

You’re likely already familiar with some of the aggregation functions in LINQ or F# collections, such as Sum, Average, Min, Max, and Count (see figure 18.1). All of these have a common signature: they take in a sequence of elements of type T and return ...