By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Exempt Show and Read instances that ignore what they are given The ban exists because a written Show is a second serialisation that drifts from the type it prints. An instance whose every method discards all of its arguments cannot drift: what it produces does not depend on the type at all. That is also the shape a secret takes when the point is to keep it out of every log line, which the guide has always allowed, so it is now the rule rather than a suppression at every such instance. Recognised syntactically: every method the instance writes out has at least one argument pattern and every one of them is a wildcard. Constructor patterns are not enough, because `show Red = "red"` reads the value while binding nothing, and an instance with no methods written out says nothing about what its class defaults do with the value.