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Tomer Ben David (8) [Avatar] Offline
#1
The text says:

The computation op in the earlier
section is a Function1 that may need to be composed with a monadic pipeline containing a
List or an Option. We need monad transformers for this kind of composition 22 . But
Function1 doesn’t have any transformer that can be used to stack up our computation into a
monadic pipeline. We solve this by introducing another level of indirection. We wrap
Function1 into another abstraction that we call Reader. And as we will see in chapter 5
Reader can have a transformer ReaderT, which can be used to compose other monads with
the Reader.


but there is only implementation of reader monad for usage without any optional / list. it would be extremely useful at this point to see a real example as the text says for Option/List where the reader monad would actually help us!
Debasish Ghosh (116) [Avatar] Offline
#2
Thanks for reporting. Have taken note of it. Will address in an upcoming MEAP.
Debasish Ghosh (116) [Avatar] Offline
#3
I was going to add some examples but then I found Listing 3.8 gives an example of composing this Reader with Try. List and/or Option should be exactly similar.

Thanks.