text-conversions-0.2.0: Safe conversions between textual types

Safe HaskellSafe
LanguageHaskell2010

Data.Text.Conversions

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

Documentation

class Functor f => DecodeText f a where Source #

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.

Minimal complete definition

decodeText

Methods

decodeText :: a -> f Text Source #

class FromText a where Source #

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

Minimal complete definition

fromText

Methods

fromText :: Text -> a Source #

class ToText a where Source #

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.

Minimal complete definition

toText

Methods

toText :: a -> Text Source #

newtype UTF8 a Source #

Simple wrapper type that is used to select a desired encoding when encoding or decoding text from binary data, such as ByteStrings.

Constructors

UTF8 

Fields

Instances

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

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 Source #

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:

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