| Copyright | (C) 2015 Edward Kmett |
|---|---|
| License | BSD-style (see the file LICENSE) |
| Maintainer | Edward Kmett <ekmett@gmail.com> |
| Stability | experimental |
| Portability | non-portable |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Data.Constraint.Deferrable
Description
The idea for this trick comes from Dimitrios Vytiniotis.
- data UnsatisfiedConstraint = UnsatisfiedConstraint String
- class Deferrable p where
- deferEither :: proxy p -> (p => r) -> Either String r
- defer :: forall proxy p r. Deferrable p => proxy p -> (p => r) -> r
- deferred :: forall p. Deferrable p :- p
Documentation
data UnsatisfiedConstraint Source
Constructors
| UnsatisfiedConstraint String |
class Deferrable p where Source
Allow an attempt at resolution of a constraint at a later time
Methods
deferEither :: proxy p -> (p => r) -> Either String r Source
Resolve a Deferrable constraint with observable failure.
Instances
| (Deferrable a, Deferrable b) => Deferrable (a, b) Source | |
| (Typeable * a, Typeable * b) => Deferrable ((~) * a b) Source | |
| (Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c) Source |
defer :: forall proxy p r. Deferrable p => proxy p -> (p => r) -> r Source
Defer a constraint for later resolution in a context where we want to upgrade failure into an error
deferred :: forall p. Deferrable p :- p Source