Safe Haskell	None
Language	Haskell2010

PredicateTransformers

Description

This library is based on the notion of a predicate transformer, the below type PT a b, which is a function from a to predicates on b. They act as a sort of compositional "matcher language". Composing these predicate transformers is meant to be analogous to composing optics and there are utilities for using predicate transformers with (lens-style) optics.

Some predicate transformers provided by other libraries: all, any (base) either (base) allOf (lens)

Synopsis

class Predicatory a where
- oneOfTwo :: a -> a -> a
- also :: a -> a -> a
- stop :: a
- continue :: a
class Exceptional a where
- assess :: a -> IO ()
data PredicateFailed = PredicateFailed
type Pred a = a -> Bool
type PT p a b = (a -> p) -> b -> p
match :: Predicatory p => APrism s t a b -> PT p a s
just :: Predicatory p => PT p a (Maybe a)
left :: Predicatory p => PT p e (Either e a)
right :: Predicatory p => PT p a (Either e a)
endingWith :: (Predicatory p, Foldable f) => PT p a (f a)
startingWith :: (Predicatory p, Foldable f) => PT p a (f a)
only :: (Predicatory p, Foldable f) => PT p a (f a)
kth :: (Predicatory p, Foldable f) => Int -> PT p a (f a)
list :: Predicatory p => [a -> p] -> [a] -> p
dist :: (Predicatory p, Eq (f ()), Functor f, Foldable f) => f (a -> p) -> f a -> p
distRep :: Representable f => f (a -> p) -> f a -> f p
allTrue :: (Predicatory p, Foldable f) => f (a -> p) -> a -> p
allOf1 :: Predicatory p => Fold s a -> PT p a s
(==>) :: a -> b -> (a, b)
pair :: Predicatory p => (a -> p) -> (b -> p) -> (a, b) -> p
(!) :: (b -> a) -> (a -> c) -> b -> c
traced :: Show a => (a -> c) -> a -> c
traceFail :: (Predicatory p, Exceptional p) => (a -> String) -> PT p a a
traceFailShow :: (Exceptional p, Predicatory p, Show a) => PT p a a
something :: Predicatory p => a -> p
forced :: (Predicatory p, NFData a) => a -> p

Documentation

class Predicatory a where Source #

Methods

oneOfTwo :: a -> a -> a Source #

also :: a -> a -> a Source #

stop :: a Source #

continue :: a Source #

Instances

Instances details

Predicatory Bool Source #
Instance details Defined in PredicateTransformers Methods oneOfTwo :: Bool -> Bool -> Bool Source # also :: Bool -> Bool -> Bool Source # stop :: Bool Source # continue :: Bool Source #
Predicatory (IO ()) Source #
Instance details Defined in PredicateTransformers Methods oneOfTwo :: IO () -> IO () -> IO () Source # also :: IO () -> IO () -> IO () Source # stop :: IO () Source # continue :: IO () Source #

class Exceptional a where Source #

Methods

assess :: a -> IO () Source #

Instances

Instances details

Exceptional Bool Source #
Instance details Defined in PredicateTransformers Methods assess :: Bool -> IO () Source #
Exceptional (IO ()) Source #
Instance details Defined in PredicateTransformers Methods assess :: IO () -> IO () Source #

data PredicateFailed Source #

Constructors

PredicateFailed

Instances

Instances details

Show PredicateFailed Source #
Instance details Defined in PredicateTransformers Methods showsPrec :: Int -> PredicateFailed -> ShowS # show :: PredicateFailed -> String # showList :: [PredicateFailed] -> ShowS #
Exception PredicateFailed Source #
Instance details Defined in PredicateTransformers Methods toException :: PredicateFailed -> SomeException # fromException :: SomeException -> Maybe PredicateFailed # displayException :: PredicateFailed -> String #

type Pred a = a -> Bool Source #

A convenient alias for predicates.

type PT p a b = (a -> p) -> b -> p Source #

Predicate transformers form a category where composition is ordinary function composition. Forms a category with . and id. Multiple are already provided by the standard library, for instance all and any.

match :: Predicatory p => APrism s t a b -> PT p a s Source #

Operate on the target of a prism, or fail.

just :: Predicatory p => PT p a (Maybe a) Source #

Operate on the Just branch of a Maybe, or fail.

left :: Predicatory p => PT p e (Either e a) Source #

Operate on the Left branch of an Either, or fail.

right :: Predicatory p => PT p a (Either e a) Source #

Operate on the Right branch of an Either, or fail.

endingWith :: (Predicatory p, Foldable f) => PT p a (f a) Source #

Operate on the last value in a foldable, or fail if it's not present.

startingWith :: (Predicatory p, Foldable f) => PT p a (f a) Source #

Operate on the first value in a foldable, or fail if it's not present.

only :: (Predicatory p, Foldable f) => PT p a (f a) Source #

Require that a foldable has a single element, and operate on that element.

kth :: (Predicatory p, Foldable f) => Int -> PT p a (f a) Source #

Only test the kth element of a foldable.

list :: Predicatory p => [a -> p] -> [a] -> p Source #

Given a list of predicates and a list of values, ensure that each predicate holds for each respective value. Fails if the two lists have different lengths.

dist :: (Predicatory p, Eq (f ()), Functor f, Foldable f) => f (a -> p) -> f a -> p Source #

Given a functor-full of predicates, and a functor-full of values, ensure that the structures of the two functors match and apply all of the predicates to all of the values. Generalized version of list.

distRep :: Representable f => f (a -> p) -> f a -> f p Source #

Given a representable functor-full of predicates, and a functor-full of values, yield a representable functor-full of booleans. Similar to dist.

allTrue :: (Predicatory p, Foldable f) => f (a -> p) -> a -> p Source #

Test all predicates against one value.

allOf1 :: Predicatory p => Fold s a -> PT p a s Source #

Check that a predicate is true for all values behind a generalized getter and that there's at least one value for which it's true.

(==>) :: a -> b -> (a, b) Source #

Sugar for tupling.

pair :: Predicatory p => (a -> p) -> (b -> p) -> (a, b) -> p Source #

(!) :: (b -> a) -> (a -> c) -> b -> c Source #

Flipped function composition; f ! for a function f is a predicate transformer.

traced :: Show a => (a -> c) -> a -> c Source #

Prints the input of a predicate, for debugging.

traceFail :: (Predicatory p, Exceptional p) => (a -> String) -> PT p a a Source #

Prints the input of a predicate, if the predicate fails. Requires that the predicate's output type includes a notion of failure.

traceFailShow :: (Exceptional p, Predicatory p, Show a) => PT p a a Source #

something :: Predicatory p => a -> p Source #

Predicate which always succeeds.

forced :: (Predicatory p, NFData a) => a -> p Source #

Predicate which triggers full evaluation of its input and succeeds. Useful for testing that an exception isn't thrown.