Terminal functions

Terminal functions are eagerly executed. They execute immediately and once executed, they execute all the previous intermediate, lazy functions in the call chain. Terminal functions either return a single value or produce a side effect. The reduce example, we saw earlier, returns a single value: 1. The ForEach function does not return a value but can produce a side effect, such as printing out each item. The Collect, Join, and GroupBy functions group items in a collection.