The unit test definition seems to be out of date with the version of HSpec used:

/tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:40:20:
    Ambiguous occurrence `pendingWith'
    It could refer to either `SimpleInteractiveInterpreter.Test.pendingWith',
                             defined at /tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:71:1
                          or `Test.Hspec.pendingWith',
                             imported from `Test.Hspec' at /tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:4:1-17
                             (and originally defined in `hspec-1.12.1:Test.Hspec.Core.Type')

The unit test definition seems to be out of date with the version of HSpec used:

/tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:40:20:
    Ambiguous occurrence `pendingWith'
    It could refer to either `SimpleInteractiveInterpreter.Test.pendingWith',
                             defined at /tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:71:1
                          or `Test.Hspec.pendingWith',
                             imported from `Test.Hspec' at /tmp/haskell11634-20-12vowd8/SimpleInteractiveInterpreter/Test.hs:4:1-17
                             (and originally defined in `hspec-1.12.1:Test.Hspec.Core.Type')

I think it's way too easy. Just playing type tetris / cat-programming ("if it fits, it sits") can be used to solve it in a couple minutes without actually having to think about it.

Closed type families were introduced in 7.8.1.

The fact that it doesn't use (and doesn't even seem to allow!) closed type families is potentially teaching an obsolete pattern.