Display

Display human-readable values to the user efficiently. See the display method for documentation.

Use the OverloadedStrings language extension when using this module to produce Builder values conveniently e.g. "Hello" <> display name.

Printing method

display :: Display a => a -> Builder

Display a value in a human-readable format. This is the opposite of the Show class which is intended for programmers to read. See Display for how to use this for your own types.

• Writing to file or output: The Builder can be written directly to a handle with hPutBuilder very efficiently as UTF-8. This is the preferred method when writing to stdout or a file.
• Writing to a string: Use one of the functions in Conversions like displayByteString or displayString (when needed).

Use the functions in Data.ByteString.Builder for hex encodings of numbers and strings.

To append Builder you can use the Monoid instance, for example to print things comma-separated, you can use intersperse and mconcat:

mconcat (intersperse ", " (map display [1, 4, 5]))

This example requires the OverloadedStrings language extension.

Conversions

displayByteString :: Display a => a -> ByteString

Display to a ByteString value.

displayLazyByteString :: Display a => a -> ByteString

Display to a ByteString value.

displayString :: Display a => a -> String

Display to a String value. Very inefficient. Only use when you are forced to by another API.

displayText :: Display a => a -> Text

Display to a Text value. Inefficient. Only use when you have to.

displayLazyText :: Display a => a -> Text

Display to a Text value. Inefficient. Only use when you have to.

The class

class Display a where

Display a value in a human-readable format. This is the opposite of the Show class which is intended for programmers to read, and can be used alongside Show.

For example, consider: Maybe String

>>> show (Just "abc")
Just "abc"
>>> show Nothing
Nothing

whereas display is meant for printing to users, so you might write this:

>>> display (Just "abc")
abc
>>> display Nothing
""

You can safely use newtype deriving with this type, e.g.

newtype Name = Name Text deriving (Show, Display)

Instances for exceptions can be written like this:

data MyException = SomeProblem deriving (Show, Typeable)
instance Exception MyException where displayException = displayString

Minimal complete definition

display

Methods

display :: a -> Builder

Display a value in a human-readable format. This is the opposite of the Show class which is intended for programmers to read. See Display for how to use this for your own types.

• Writing to file or output: The Builder can be written directly to a handle with hPutBuilder very efficiently as UTF-8. This is the preferred method when writing to stdout or a file.
• Writing to a string: Use one of the functions in Conversions like displayByteString or displayString (when needed).

Use the functions in Data.ByteString.Builder for hex encodings of numbers and strings.

To append Builder you can use the Monoid instance, for example to print things comma-separated, you can use intersperse and mconcat:

mconcat (intersperse ", " (map display [1, 4, 5]))

This example requires the OverloadedStrings language extension.

Instances

Display Char

Methods

display :: Char -> Builder

Display Double

Methods

display :: Double -> Builder

Display Float

Methods

display :: Float -> Builder

Display Int

Methods

display :: Int -> Builder

Display Int8

Methods

display :: Int8 -> Builder

Display Int16

Methods

display :: Int16 -> Builder

Display Int32

Methods

display :: Int32 -> Builder

Display Int64

Methods

display :: Int64 -> Builder

Display Integer

Methods

display :: Integer -> Builder

Display Word

Methods

display :: Word -> Builder

Display Word8

Methods

display :: Word8 -> Builder

Display Word16

Methods

display :: Word16 -> Builder

Display Word32

Methods

display :: Word32 -> Builder

Display Word64

Methods

display :: Word64 -> Builder

Display ByteString

Methods

display :: ByteString -> Builder

Display ByteString

Methods

display :: ByteString -> Builder

Display Builder

Methods

display :: Builder -> Builder

Display Text

Methods

display :: Text -> Builder

Display Text

Methods

display :: Text -> Builder

Display [Char]

Methods

display :: [Char] -> Builder

Display a => Display (Maybe a)

Methods

display :: Maybe a -> Builder

(Display a, Display b) => Display (Either a b)

Methods

display :: Either a b -> Builder