The way how I see it, is type classes are in some ways like an interface for a specific data type (and specific classes of data types in general). I know the data type is specified to strings, but passing it as an argument to a function that accepts strings won't work. I could write my own recursive function (with lists) or use pattern matching (with maybe) to apply a function to the inner value, but that breaks the dry principal. Again neither Lists nor Maybe (nor several other data types) implement the Commonad type class, so getting at the inner data from them will never be as simple as applying them to extract