Text.Show.Text.TH

Functions to mechanically derive Show instances or splice show-related expressions into Haskell source code. You need to enable the TemplateHaskell language extension in order to use this module.

deriveShow

deriveShow automatically generates a Show instance declaration for a data type or newtype. As an example:

{-# LANGUAGE TemplateHaskell #-}
import Text.Show.Text.TH (deriveShow)

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

D now has a Show instance equivalent to that which would be generated by a deriving Show clause.

Note that at the moment, deriveShow does not support data families, so it is impossible to use deriveShow with data instances or newtype instances. Also, deriveShow lacks the ability to properly detect data types with higher-kinded type parameters (e.g., data HK f a = HK (f a)), so it cannot create instances for them either.

deriveShow :: Name -> Q [Dec]

Generates a Show instance declaration for the given data type or newtype.

mk functions

There may be scenarios in which you want to show an arbitrary data type or newtype without having to make the type an instance of Show. For these cases, Text.Show.Text.TH provide several functions (all prefixed with mk) that splice the appropriate lambda expression into your source code.

As an example, suppose you have data ADT = ADTCon, which is not an instance of Show. With mkShow, you can still convert it to Text:

{-# LANGUAGE OverloadedStrings, TemplateHaskell #-}

whichADT :: Bool
whichADT = $(mkShow ''ADT) ADTCon == "ADT"

Note that due the order in which Template Haskell executes splices, the above code may fail to compile if ADT is located in the same module and whichADT. To get around this, you can use the following hack:

{-# LANGUAGE OverloadedStrings, TemplateHaskell #-}

data ADT = ADTCon
$(return [])

whichADT :: Bool
whichADT = $(mkShow ''ADT) ADTCon == "ADT"

mkShow :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a strict Text.

mkShowLazy :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a lazy Text.

mkShowPrec :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a strict Text with the given precedence.

mkShowPrecLazy :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a lazy Text with the given precedence.

mkShowb :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a Builder.

mkShowbPrec :: Name -> Q Exp

Generates a lambda expression which converts the given data type or newtype to a Builder with the given precedence.

mkPrint :: Name -> Q Exp

Generates a lambda expression which writes the given data type or newtype argument's strict Text output to the standard output, followed by a newline.

mkPrintLazy :: Name -> Q Exp

Generates a lambda expression which writes the given data type or newtype argument's lazy Text output to the standard output, followed by a newline.

mkHPrint :: Name -> Q Exp

Generates a lambda expression which writes the given data type or newtype argument's strict Text output to the given file handle, followed by a newline.

mkHPrintLazy :: Name -> Q Exp

Generates a lambda expression which writes the given data type or newtype argument's lazy Text output to the given file handle, followed by a newline.