Safe Haskell | Safe |
---|---|
Language | Haskell2010 |
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
- class ToText a where
- class Functor f => DecodeText f 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 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.
However, you probably do not want to call fromText
directly; call
convertText
, instead.
Instances
FromText String Source # | |
FromText Text Source # | |
FromText Text Source # | |
FromText (Maybe (Base64 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (Maybe (Base64 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (Maybe (Base16 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (Maybe (Base16 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions | |
FromText (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions |
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.
Instances
ToText String Source # | |
ToText Text Source # | |
ToText Text Source # | |
ToText (Base64 ByteString) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base64 ByteString) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base16 ByteString) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base16 ByteString) Source # | |
Defined in Data.Text.Conversions |
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.
decodeText :: a -> f Text Source #
Instances
DecodeText Maybe (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions decodeText :: UTF8 ByteString -> Maybe Text Source # | |
DecodeText Maybe (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions decodeText :: UTF8 ByteString -> Maybe Text Source # |
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
:
>>>
decodeConvertText (UTF8 ("hello" :: ByteString)) :: Maybe Text
Just "hello"
Encoding newtypes
Simple wrapper type that is used to select a desired encoding when encoding or
decoding text from binary data, such as ByteString
s. 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
Instances
Functor UTF8 Source # | |
DecodeText Maybe (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions decodeText :: UTF8 ByteString -> Maybe Text Source # | |
DecodeText Maybe (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions decodeText :: UTF8 ByteString -> Maybe Text Source # | |
Eq a => Eq (UTF8 a) Source # | |
Show a => Show (UTF8 a) Source # | |
FromText (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions | |
FromText (UTF8 ByteString) Source # | |
Defined in Data.Text.Conversions |
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.
Instances
Functor Base16 Source # | |
Eq a => Eq (Base16 a) Source # | |
Show a => Show (Base16 a) Source # | |
FromText (Maybe (Base16 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (Maybe (Base16 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base16 ByteString) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base16 ByteString) Source # | |
Defined in Data.Text.Conversions |
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.
Instances
Functor Base64 Source # | |
Eq a => Eq (Base64 a) Source # | |
Show a => Show (Base64 a) Source # | |
FromText (Maybe (Base64 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
FromText (Maybe (Base64 ByteString)) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base64 ByteString) Source # | |
Defined in Data.Text.Conversions | |
ToText (Base64 ByteString) Source # | |
Defined in Data.Text.Conversions |