| Copyright | (c) Justin Le 2019 |
|---|---|
| License | BSD3 |
| Maintainer | justin@jle.im |
| Stability | experimental |
| Portability | non-portable |
| Safe Haskell | Safe-Inferred |
| Language | Haskell2010 |
Data.Functor.Contravariant.Conclude
Description
Documentation
class Decide f => Conclude f where Source #
The contravariant analogue of Plus. Adds on to
Decide the ability to express a combinator that rejects all input, to
act as the dead-end. Essentially Decidable without a superclass
constraint on Divisible.
If one thinks of f a as a consumer of as, then conclude defines
a consumer that cannot ever receive any input.
Conclude acts as an identity with decide, because any decision that
involves conclude must necessarily always pick the other option.
That is, for, say,
decidef xconcluded
f is the deciding function that picks which of the inputs of decide
to direct input to; in the situation above, f must always direct all
input to x, and never concluded.
Mathematically, a functor being an instance of Decide means that it is
"monoidal" with respect to the contravariant "either-based" Day
convolution described in the documentation of Decide. On top of
Decide, it adds a way to construct an "identity" conclude where
decide f x (conclude q) == x, and decide g (conclude r) y == y.