[Haskell-cafe] Design Question - Functions taking 'subtype' like arguments but has to be restricted to one type

[Imants Cekusins]

Beware: if you go with Either and combine Either ops with >>=, first Left
result stops evaluation and returns 1st Left result. Right results continue
evaluation. If this is expected, Either fits.

If more ops are expected after 'update count' no-op (if Left stands for
Frozen), then Either and >>= should not be used together.

Algebraic type (Flex count | Frozen count) is also suitable. Let the
calling functions decide how to process Frozen values. At least they'll
know the difference.
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