Go back to using One in result types and use a widening method at the |@| site.
Go back to using One as the result types and invoking a widening method
at the |@| call site.
Improved comments and names.
Use methods that return bare Strings and then added a toAccList method to lift
those into a List for the |@| operator.
Use String not ErrorMessage in \/ examples (other than Every) to be more
idiomatic.