Safe Haskell	Safe-Inferred
Language	Haskell2010

Data.Text.Conversions

Contents

Conversion typeclasses and functions
Encoding newtypes

Description

This module provides a set of typeclasses for safely converting between textual data. The built-in String type, as well as strict Text and lazy Text, are safely convertible between one another. The ByteString type is frequently treated in much the same manner, but this is unsafe for two reasons:

Since ByteString encodes binary data, it does not specify a particular encoding, so assuming a particular encoding like UTF-8 would be incorrect.
Furthermore, decoding binary data into text given a particular encoding can fail. Most systems simply use decodeUtf8 and similar functions, which will dangerously throw exceptions when given invalid data.

This module addresses both problems by providing a DecodeText typeclass for decoding binary data in a way that can fail and by providing a UTF8 wrapper type for selecting the desired encoding.

Most of the time, you will not need to create your own instances or use the underlying functions that make the conversion machinery tick. Instead, just use the convertText method to convert between two textual datatypes or the decodeConvertText method to perform a conversion that can fail.

Examples:

>>> convertText ("hello" :: String) :: Text
"hello"
>>> decodeConvertText (UTF8 ("hello" :: ByteString)) :: Maybe Text
Just "hello"
>>> decodeConvertText (UTF8 ("\xc3\x28" :: ByteString)) :: Maybe Text
Nothing

Synopsis

class FromText a where
- fromText :: Text -> a
class ToText a where
- toText :: a -> Text
class Functor f => DecodeText (f :: Type -> Type) a where
- decodeText :: a -> f Text
convertText :: (ToText a, FromText b) => a -> b
decodeConvertText :: (DecodeText f a, FromText b) => a -> f b
newtype UTF8 a = UTF8 {
- unUTF8 :: a
}
newtype Base16 a = Base16 {
- unBase16 :: a
}
newtype Base64 a = Base64 {
- unBase64 :: a
}

Conversion typeclasses and functions

class FromText a where #

A simple typeclass that handles converting Text to arbitrary datatypes. If you have a type that can be produced from text, implement this typeclass. However, you probably do not want to call fromText directly; call convertText, instead.

Methods

fromText :: Text -> a #

Instances

Instances details

FromText Text #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Text #
FromText Text #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Text #
FromText String #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> String #
FromText (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> UTF8 ByteString #
FromText (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> UTF8 ByteString #
FromText (Maybe (Base16 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base16 ByteString) #
FromText (Maybe (Base16 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base16 ByteString) #
FromText (Maybe (Base64 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base64 ByteString) #
FromText (Maybe (Base64 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base64 ByteString) #

class ToText a where #

A simple typeclass that handles converting arbitrary datatypes to Text when the operation cannot fail. If you have a type that satisfies that requirement, implement this typeclass, but if the operation can fail, use DecodeText instead.

Methods

toText :: a -> Text #

Instances

Instances details

ToText Text #
Instance details Defined in Data.Text.Conversions Methods toText :: Text -> Text #
ToText Text #
Instance details Defined in Data.Text.Conversions Methods toText :: Text -> Text #
ToText String #
Instance details Defined in Data.Text.Conversions Methods toText :: String -> Text #
ToText (Base16 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base16 ByteString -> Text #
ToText (Base16 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base16 ByteString -> Text #
ToText (Base64 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base64 ByteString -> Text #
ToText (Base64 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base64 ByteString -> Text #

class Functor f => DecodeText (f :: Type -> Type) a where #

A simple typeclass that handles converting arbitrary datatypes to Text when the operation can fail. If you have a type that satisfies that requirement, implement this typeclass, but if the operation cannot fail, use ToText instead.

Methods

decodeText :: a -> f Text #

Instances

Instances details

DecodeText Maybe (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods decodeText :: UTF8 ByteString -> Maybe Text #
DecodeText Maybe (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods decodeText :: UTF8 ByteString -> Maybe Text #

convertText :: (ToText a, FromText b) => a -> b #

A function that provides a way to safely convert between arbitrary textual datatypes where the conversion to text cannot fail.

>>> convertText ("hello" :: String) :: Text
"hello"

decodeConvertText :: (DecodeText f a, FromText b) => a -> f b #

A function that provides a way to safely convert between arbitrary textual datatypes where the conversion to text can fail, such as decoding binary data to text. Since binary data can represent text in many different potential encodings, it is necessary to use a newtype that picks the particular encoding, like UTF8:

>>> decodeConvertText (UTF8 ("hello" :: ByteString)) :: Maybe Text
Just "hello"

Encoding newtypes

newtype UTF8 a #

Simple wrapper type that is used to select a desired encoding when encoding or decoding text from binary data, such as ByteStrings. The conversion is not partial; it will result in Nothing when a ByteString is provided with data that is not valid in UTF-8.

>>> convertText ("hello" :: Text) :: UTF8 ByteString
UTF8 "hello"
>>> decodeConvertText (UTF8 ("hello" :: ByteString)) :: Maybe Text
Just "hello"
>>> decodeConvertText (UTF8 ("invalid \xc3\x28" :: ByteString)) :: Maybe Text
Nothing

Constructors

UTF8
Fields unUTF8 :: a

Instances

Instances details

Functor UTF8 #
Instance details Defined in Data.Text.Conversions Methods fmap :: (a -> b) -> UTF8 a -> UTF8 b # (<$) :: a -> UTF8 b -> UTF8 a #
DecodeText Maybe (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods decodeText :: UTF8 ByteString -> Maybe Text #
DecodeText Maybe (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods decodeText :: UTF8 ByteString -> Maybe Text #
Show a => Show (UTF8 a) #
Instance details Defined in Data.Text.Conversions Methods showsPrec :: Int -> UTF8 a -> ShowS # show :: UTF8 a -> String # showList :: [UTF8 a] -> ShowS #
Eq a => Eq (UTF8 a) #
Instance details Defined in Data.Text.Conversions Methods (==) :: UTF8 a -> UTF8 a -> Bool # (/=) :: UTF8 a -> UTF8 a -> Bool #
FromText (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> UTF8 ByteString #
FromText (UTF8 ByteString) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> UTF8 ByteString #

newtype Base16 a #

Wrapper type used to select a base 16 encoding when encoding or decoding binary data. Safe because base 16 encoding will always produce ASCII output.

Constructors

Base16
Fields unBase16 :: a

Instances

Instances details

Functor Base16 #
Instance details Defined in Data.Text.Conversions Methods fmap :: (a -> b) -> Base16 a -> Base16 b # (<$) :: a -> Base16 b -> Base16 a #
Show a => Show (Base16 a) #
Instance details Defined in Data.Text.Conversions Methods showsPrec :: Int -> Base16 a -> ShowS # show :: Base16 a -> String # showList :: [Base16 a] -> ShowS #
Eq a => Eq (Base16 a) #
Instance details Defined in Data.Text.Conversions Methods (==) :: Base16 a -> Base16 a -> Bool # (/=) :: Base16 a -> Base16 a -> Bool #
FromText (Maybe (Base16 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base16 ByteString) #
FromText (Maybe (Base16 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base16 ByteString) #
ToText (Base16 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base16 ByteString -> Text #
ToText (Base16 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base16 ByteString -> Text #

newtype Base64 a #

Wrapper type used to select a base 64 encoding when encoding or decoding binary data. Safe because base 64 encoding will always produce ASCII output.

Constructors

Base64
Fields unBase64 :: a

Instances

Instances details

Functor Base64 #
Instance details Defined in Data.Text.Conversions Methods fmap :: (a -> b) -> Base64 a -> Base64 b # (<$) :: a -> Base64 b -> Base64 a #
Show a => Show (Base64 a) #
Instance details Defined in Data.Text.Conversions Methods showsPrec :: Int -> Base64 a -> ShowS # show :: Base64 a -> String # showList :: [Base64 a] -> ShowS #
Eq a => Eq (Base64 a) #
Instance details Defined in Data.Text.Conversions Methods (==) :: Base64 a -> Base64 a -> Bool # (/=) :: Base64 a -> Base64 a -> Bool #
FromText (Maybe (Base64 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base64 ByteString) #
FromText (Maybe (Base64 ByteString)) #
Instance details Defined in Data.Text.Conversions Methods fromText :: Text -> Maybe (Base64 ByteString) #
ToText (Base64 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base64 ByteString -> Text #
ToText (Base64 ByteString) #
Instance details Defined in Data.Text.Conversions Methods toText :: Base64 ByteString -> Text #