snoyberg
commented
6 years ago Sounds fine to me, want to send a PR?
On Mon, Jan 15, 2018 at 7:44 PM, Daniel Killebrew notifications@github.com wrote:
Problem:
singleton is not implemented for NonEmpty This does not make sense; obviously you can create a NonEmpty from a single element. Details:
- singleton has the constraint IsSequence seq.
- Monoid is a superclass of IsSequence
- NonEmpty is not an instance Monoid. This makes sense because there's no valid mempty.
- Thus singleton is not implemented for NonEmpty. This does not make sense because you can obviously create a valid NonEmpty container from a single element. The workaround is to use not-well-known functions like opoint or pure to create a NonEmpty. This makes my code less readable, because those functions are not well known (opoint) or not typically used to create a container (pure).
Solution:
Change singleton constraint to MonoPointed. That's all.
The implementation of singleton is: singleton = opoint which only requires a MonoPointed constraint, as opoint is a function of that type class. NonEmpty already is an instance of MonoPointed, so after changing the constraint, singleton will be implemented for NonEmpty.
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gittywithexcitement
Problem:
singletonis not implemented forNonEmptyThis does not make sense; obviously you can create aNonEmptyfrom a single element.Details:
singletonhas the constraintIsSequence seq.Monoidis a superclass ofIsSequenceNonEmptyis not an instanceMonoid. This makes sense because there's no validmempty.singletonis not implemented forNonEmpty. This does not make sense because you can obviously create a validNonEmptycontainer from a single element. The workaround is to use not-well-known functions likeopointorpureto create aNonEmpty. This makes my code less readable, because those functions are not well known (opoint) or not typically used to create a container (pure).Solution:
Change
singletonconstraint toMonoPointed. That's all.The implementation of
singletonis:singleton = opointwhich only requires aMonoPointedconstraint, asopointis a function of that type class.NonEmptyalready is an instance ofMonoPointed, so after changing the constraint,singletonwill be implemented forNonEmpty.