Data.Functor.Classes

instance (Eq1 f) => Eq1 (T f) where ...
instance (Ord1 f) => Ord1 (T f) where ...
instance (Read1 f) => Read1 (T f) where ...
instance (Show1 f) => Show1 (T f) where ...

instance (Eq1 f, Eq a) => Eq (T f a) where (==) = eq1
instance (Ord1 f, Ord a) => Ord (T f a) where compare = compare1
instance (Read1 f, Read a) => Read (T f a) where readsPrec = readsPrec1
instance (Show1 f, Show a) => Show (T f a) where showsPrec = showsPrec1

Liftings of Prelude classes

For unary constructors

class Eq1 f where Source

Lifting of the Eq class to unary type constructors.

eq1 :: (Eq1 f, Eq a) => f a -> f a -> Bool Source

Lift the standard (==) function through the type constructor.

class Eq1 f => Ord1 f where Source

Lifting of the Ord class to unary type constructors.

compare1 :: (Ord1 f, Ord a) => f a -> f a -> Ordering Source

Lift the standard compare function through the type constructor.

class Read1 f where Source

Lifting of the Read class to unary type constructors.

readsPrec1 :: (Read1 f, Read a) => Int -> ReadS (f a) Source

Lift the standard readsPrec and readList functions through the type constructor.

class Show1 f where Source

Lifting of the Show class to unary type constructors.

showsPrec1 :: (Show1 f, Show a) => Int -> f a -> ShowS Source

Lift the standard showsPrec and showList functions through the type constructor.

For binary constructors

class Eq2 f where Source

Lifting of the Eq class to binary type constructors.

eq2 :: (Eq2 f, Eq a, Eq b) => f a b -> f a b -> Bool Source

Lift the standard (==) function through the type constructor.

class Eq2 f => Ord2 f where Source

Lifting of the Ord class to binary type constructors.

compare2 :: (Ord2 f, Ord a, Ord b) => f a b -> f a b -> Ordering Source

Lift the standard compare function through the type constructor.

class Read2 f where Source

Lifting of the Read class to binary type constructors.

readsPrec2 :: (Read2 f, Read a, Read b) => Int -> ReadS (f a b) Source

Lift the standard readsPrec function through the type constructor.

class Show2 f where Source

Lifting of the Show class to binary type constructors.

showsPrec2 :: (Show2 f, Show a, Show b) => Int -> f a b -> ShowS Source

Lift the standard showsPrec function through the type constructor.

Helper functions

These functions can be used to assemble Read and Show instances for new algebraic types. For example, given the definition

data T f a = Zero a | One (f a) | Two a (f a)

a standard Read1 instance may be defined as

instance (Read1 f) => Read1 (T f) where
    liftReadsPrec rp rl = readsData $
        readsUnaryWith rp "Zero" Zero `mappend`
        readsUnaryWith (liftReadsPrec rp rl) "One" One `mappend`
        readsBinaryWith rp (liftReadsPrec rp rl) "Two" Two

and the corresponding Show1 instance as

instance (Show1 f) => Show1 (T f) where
    liftShowsPrec sp _ d (Zero x) =
        showsUnaryWith sp "Zero" d x
    liftShowsPrec sp sl d (One x) =
        showsUnaryWith (liftShowsPrec sp sl) "One" d x
    liftShowsPrec sp sl d (Two x y) =
        showsBinaryWith sp (liftShowsPrec sp sl) "Two" d x y

readsData :: (String -> ReadS a) -> Int -> ReadS a Source

readsData p d is a parser for datatypes where each alternative begins with a data constructor. It parses the constructor and passes it to p. Parsers for various constructors can be constructed with readsUnary, readsUnary1 and readsBinary1, and combined with mappend from the Monoid class.

readsUnaryWith :: (Int -> ReadS a) -> String -> (a -> t) -> String -> ReadS t Source

readsUnaryWith rp n c n' matches the name of a unary data constructor and then parses its argument using rp.

readsBinaryWith :: (Int -> ReadS a) -> (Int -> ReadS b) -> String -> (a -> b -> t) -> String -> ReadS t Source

readsBinaryWith rp1 rp2 n c n' matches the name of a binary data constructor and then parses its arguments using rp1 and rp2 respectively.

showsUnaryWith :: (Int -> a -> ShowS) -> String -> Int -> a -> ShowS Source

showsUnaryWith sp n d x produces the string representation of a unary data constructor with name n and argument x, in precedence context d.

showsBinaryWith :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> String -> Int -> a -> b -> ShowS Source

showsBinaryWith sp1 sp2 n d x y produces the string representation of a binary data constructor with name n and arguments x and y, in precedence context d.

Obsolete helpers

readsUnary :: Read a => String -> (a -> t) -> String -> ReadS t Source

readsUnary n c n' matches the name of a unary data constructor and then parses its argument using readsPrec.

readsUnary1 :: (Read1 f, Read a) => String -> (f a -> t) -> String -> ReadS t Source

readsUnary1 n c n' matches the name of a unary data constructor and then parses its argument using readsPrec1.

readsBinary1 :: (Read1 f, Read1 g, Read a) => String -> (f a -> g a -> t) -> String -> ReadS t Source

readsBinary1 n c n' matches the name of a binary data constructor and then parses its arguments using readsPrec1.

showsUnary :: Show a => String -> Int -> a -> ShowS Source

showsUnary n d x produces the string representation of a unary data constructor with name n and argument x, in precedence context d.

showsUnary1 :: (Show1 f, Show a) => String -> Int -> f a -> ShowS Source

showsUnary1 n d x produces the string representation of a unary data constructor with name n and argument x, in precedence context d.

showsBinary1 :: (Show1 f, Show1 g, Show a) => String -> Int -> f a -> g a -> ShowS Source

showsBinary1 n d x y produces the string representation of a binary data constructor with name n and arguments x and y, in precedence context d.