2013/8/13 Lukas Lehner <lehner.lukas@gmail.com>:

> Good to know extension. And without it?

Someone correct me if I'm wrong, here's how I understand it:

To execute print [], ghc has to find which instance of Show to call.
How could it find an instance without knowing the type ?
[] could be a list of anything, and while in theory we know that in
all cases it should print "[]", in practice ghc can't call that code
if it doesn't know the type of the list.

David.

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