scala and state monad: no free lunch part 2

As a follow up to my last post about no free lunch I wanted to show more state monad usage and recognize that you can change function return types in the middle of a for-comprehension. This allows each function to return different types of values from the computation along the way.

In the code below, you compose a function by using the for-comprehension. The yield part of the for-comprehension is a State object. When that state object is called, it returns a tuple of (state, value). You can use ._1 or ._2 to obtain the value of interest.

The last composed function shows an example of changing the state type (instead of changing the returned value type mentioned above)  in the middle of the for-comprehension using scalaz IndexedState's iPut and iModify. This allows you to change the type of state as you go to adapt to different function's API needs.

The entire article is at gisthub.


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