[Haskell-beginners] how to feel free of the Implementation of Data structure

[吴兴博]

1. To use the Data.List is so easy as it's in the 'prelude'. but when
I want to get some elements by index, I need to use Array, or sometime
I want to use ByteString for some good reason.
We all know It's some 'linear ordered things'. Is there some method
for me to use just one form of 'list' with every possible function on
it.

2.
f1 :: (Integral a) => a -> String
f2 :: (Integral a) => String -> a

pipe = f1 . f2
It is clear that pipe is String -> String,
but.(1)How can I know what instance that 'a' is.
    (2)How can I determine what instance of 'a' is.

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吴兴博