packages with orphaned instances only

Henning Thielemann lemming at
Sat Jan 8 22:46:42 CET 2011

Ivan Lazar Miljenovic schrieb:
> On 9 January 2011 07:20, Henning Thielemann
> <lemming at> wrote:
>> If there are multiple equally natural instances, then there should not
>> be one at all.
> It depends what you mean.  In my case, I wanted the String instance
> for Arbitrary to follow certain rules (can't be the textual
> representation of a number, can't have certain characters in it,
> etc.).

This sounds like extra wishes that require a new type or some
preprocessing within a quick check (e.g. filter out digits). You would
not be happy with a private instance for Arbitrary String anyway, since
different tests may have different requirements for the test strings (if
not today, then maybe in future).

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