Text.Show.Text.Generic

Generic versions of Show class functions, as an alternative to Text.Show.Text.TH, which uses Template Haskell. This module is only available if the compiler supports generics (on GHC, 7.2 or above).

This implementation is based off of the Generics.Deriving.Show module from the generic-deriving library.

Since: 0.6

Generic show functions

Show instances can be easily defined for data types that are Generic instances. The easiest way to do this is to use the DeriveGeneric extension.

{-# LANGUAGE DeriveGeneric #-}
import Text.Show.Text
import Text.Show.Generic (genericShowbPrec)

data D a = Nullary
         | Unary Int
         | Product String Char a
         | Record { testOne   :: Double
                  , testTwo   :: Bool
                  , testThree :: D a
                  }

instance Show a => Show (D a) where
    showbPrec = genericShowbPrec

D now has a Show instance analogous to what would be generated by a deriving Show clause.

Understanding a compiler error

Suppose you intend to tuse genericShowbPrec to define a Show instance.

data Oops = Oops
    -- forgot to add "deriving Generic" here!

instance Show Oops where
    showbPrec = genericShowbPrec

If you forget to add a deriving Generic clause to your data type, at compile-time, you will get an error message that begins roughly as follows:

No instance for (GShow (Rep Oops))

This error can be confusing, but don't let it intimidate you. The correct fix is simply to add the missing "deriving Generic" clause.

genericShow :: (Generic a, GShow (Rep a)) => a -> Text

A Generic implementation of show.

Since: 0.6

genericShowLazy :: (Generic a, GShow (Rep a)) => a -> Text

A Generic implementation of showLazy.

Since: 0.6

genericShowPrec :: (Generic a, GShow (Rep a)) => Int -> a -> Text

A Generic implementation of showPrec.

Since: 0.6

genericShowPrecLazy :: (Generic a, GShow (Rep a)) => Int -> a -> Text

A Generic implementation of showPrecLazy.

Since: 0.6

genericShowList :: (Generic a, GShow (Rep a)) => [a] -> Text

A Generic implementation of showList.

Since: 0.6

genericShowListLazy :: (Generic a, GShow (Rep a)) => [a] -> Text

A Generic implementation of showListLazy.

Since: 0.6

genericShowb :: (Generic a, GShow (Rep a)) => a -> Builder

A Generic implementation of showb.

Since: 0.6

genericShowbPrec :: (Generic a, GShow (Rep a)) => Int -> a -> Builder

A Generic implementation of showbPrec.

Since: 0.6

genericShowbList :: (Generic a, GShow (Rep a)) => [a] -> Builder

A Generic implementation of showbList.

Since: 0.6

genericPrint :: (Generic a, GShow (Rep a)) => a -> IO ()

A Generic implementation of print.

Since: 0.6

genericPrintLazy :: (Generic a, GShow (Rep a)) => a -> IO ()

A Generic implementation of printLazy.

Since: 0.6

genericHPrint :: (Generic a, GShow (Rep a)) => Handle -> a -> IO ()

A Generic implementation of hPrint.

Since: 0.6

genericHPrintLazy :: (Generic a, GShow (Rep a)) => Handle -> a -> IO ()

A Generic implementation of hPrintLazy.

Since: 0.6

The GShow class

class GShow f where

Class of generic representation types (Rep) that can be converted to a Builder.

Since: 0.6

Minimal complete definition

gShowbPrec

Methods

gShowbPrec :: ConType -> Int -> f a -> Builder

isNullary :: f a -> Bool

Instances

GShow U1

Show c => GShow (K1 i c)

(GShow a, GShow b) => GShow ((:+:) a b)

(GShow a, GShow b) => GShow ((:*:) a b)

Typeable ((* -> *) -> Constraint) GShow

GShow a => GShow (M1 D d a)

(Constructor c, GShow a) => GShow (M1 C c a)

(Selector s, GShow a) => GShow (M1 S s a)

data ConType

Whether a constructor is a record (Rec), a tuple (Tup), is prefix (Pref), or infix (Inf).

Since: 0.6

Constructors

Rec

Tup

Pref

Inf Builder

Instances

Eq ConType

Ord ConType

Show ConType

Generic ConType

Show ConType

Typeable * ConType

type Rep ConType