Data.Constraint.Deferrable

The idea for this trick comes from Dimitrios Vytiniotis.

Documentation

data UnsatisfiedConstraint

Constructors

UnsatisfiedConstraint String

Instances

Show UnsatisfiedConstraint

Methods

showsPrec :: Int -> UnsatisfiedConstraint -> ShowS

show :: UnsatisfiedConstraint -> String

showList :: [UnsatisfiedConstraint] -> ShowS

Exception UnsatisfiedConstraint

Methods

toException :: UnsatisfiedConstraint -> SomeException

fromException :: SomeException -> Maybe UnsatisfiedConstraint

displayException :: UnsatisfiedConstraint -> String

class Deferrable p where

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

Minimal complete definition

deferEither

Methods

deferEither :: proxy p -> (p => r) -> Either String r

Resolve a Deferrable constraint with observable failure.

Instances

(Deferrable a, Deferrable b) => Deferrable (a, b)

Methods

deferEither :: proxy (a, b) -> ((a, b) -> r) -> Either String r

(Typeable * a, Typeable * b) => Deferrable ((~) * a b)

Methods

deferEither :: proxy ((* ~ a) b) -> ((* ~ a) b -> r) -> Either String r

(Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c)

Methods

deferEither :: proxy (a, b, c) -> ((a, b, c) -> r) -> Either String r

defer :: forall proxy p r. Deferrable p => proxy p -> (p => r) -> r

Defer a constraint for later resolution in a context where we want to upgrade failure into an error

deferred :: forall p. Deferrable p :- p