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.

Synopsis

Documentation

Constructors

Instances

Show UnsatisfiedConstraint Source #
Methods showsPrec :: Int -> UnsatisfiedConstraint -> ShowS # show :: UnsatisfiedConstraint -> String # showList :: [UnsatisfiedConstraint] -> ShowS #
Exception UnsatisfiedConstraint Source #
Methods toException :: UnsatisfiedConstraint -> SomeException # fromException :: SomeException -> Maybe UnsatisfiedConstraint # displayException :: UnsatisfiedConstraint -> String #

Allow an attempt at resolution of a constraint at a later time

Minimal complete definition

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 #
Methods deferEither :: proxy (a, b) -> ((a, b) -> r) -> Either String r Source #
(Typeable * a, Typeable * b) => Deferrable ((~) * a b) Source #
Methods deferEither :: proxy ((* ~ a) b) -> ((* ~ a) b -> r) -> Either String r Source #
(Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c) Source #
Methods deferEither :: proxy (a, b, c) -> ((a, b, c) -> r) -> Either String r 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