I'm not sure what you expected. It's just saying it doesn't know how to print a function that takes as input a list of lists of type a0 and returns a list of lists of type a0.
Try map reverse ["abc", "123"] instead, which it does know how to print.
Try map reverse ["abc", "123"] instead, which it does know how to print.
This looks like the kind of thing I get when my C linker has horribly choked on my code, what is the benefit of displaying: M1690418375.show_M1690418375 to the user? What should I do with that piece of information?
How do I 'add an instance declaration for (GHC.Show.Show ([[a0]] -> [[a0]]))'? I'm guessing that this is basically "suggesting" I implement printing for all functions? Or just for map? I'm not sure. I'm sure I'm not doing it, and it may well not even be possible?
(i) use ghc and ghci. TryHaskell isn't actively mantained AFAIK.
(ii) if you find a cryptic error message, first google it and learn the immediate fix, without trying to understand all the details. Of course, eventually you'll have to learn the details, but there's no reason it should be a blocking issue in the beginning.
In any case this is my short-ish, inaccurate version of "the details":
1. In the interpreter, there's an implicit "print foo" when you type "foo".
2. "print foo" expects a foo of any type t as long as t is an instance of the typeclass Show, meaning there must be a show function associated with t that turns t's into Strings. Roughly, that would be as if we had a Java where the method toString (=show) is not part of Object, but rather of an interface Showable, which not all classes have to implement.
3. In Haskell, it was decided that function types shouldn't be instances of Show because they don't have a sensible show implementation. In theory you can have a show implementation that prints "this is function" for all functions, but that's of limited usefulness.
4. The compiler's error message is just an instance of a more general message: a value foo is used in a place that expects a type that's an instance of SomeTypeClass, but foo turns out to be of a type T that isn't. For instance, if you try this on ghci:
> 'a' + 'b'
5. The "M1690418375.show_M1690418375" thing is probably an artifact of the way TryHaskell was implemented. In ghci, you simply get this instead:
arising from a use of `print'