Data.Sv.Encode.Core

This module is intended to be imported qualified as follows

import Data.Sv.Encode.Core as E

To produce a CSV file from data types, build an Encode for your data type. This module contains primitives, combinators, and type class instances to help you to do so.

Encode is a Contravariant functor, as well as a Divisible and Decidable. Divisible is the contravariant form of Applicative, while Decidable is the contravariant form of Alternative. These type classes will provide useful combinators for working with Encodes.

Specialised to Encode, the function divide from Divisible has the type:

divide :: (a -> (b,c)) -> Encode b -> Encode c -> Encode a

which can be read "if a can be split into b and c, and I can handle b, and I can handle c, then I can handle a".

Here the "I can handle" part corresponds to the Encode. If we think of (covariant) functors as being "full of" a, then we can think of contravariant functors as being "able to handle" a.

How does it work? Perform the split on the a, handle the b by converting it into some text, handle the c by also converting it to some text, then put each of those text fragments into their own field in the CSV.

Similarly, the function choose from Decidable, specialsed to Encode, has the type:

choose :: (a -> Either b c) -> Encode b -> Encode c -> Encode a

which can be read "if a is either b or c, and I can handle b, and I can handle c, then I can handle a".

This works by performing the split, then checking whether b or c resulted, then using the appropriate Encode.

For an example of encoding, see Encoding.hs

Documentation

newtype Encode a

An Encode converts its argument into one or more textual fields, to be written out as CSV.

It is Semigroup, Monoid, Contravariant, Divisible, and Decidable, allowing for composition of these values to build bigger Encodes from smaller ones.

Constructors

Encode

Fields

• getEncode :: EncodeOptions -> a -> Seq Builder

Instances

Contravariant Encode

Defined in Data.Sv.Encode.Type

Methods

contramap :: (a -> b) -> Encode b -> Encode a

(>$) :: b -> Encode b -> Encode a

Divisible Encode

Defined in Data.Sv.Encode.Type

Methods

divide :: (a -> (b, c)) -> Encode b -> Encode c -> Encode a

conquer :: Encode a

Decidable Encode

Defined in Data.Sv.Encode.Type

Methods

lose :: (a -> Void) -> Encode a

choose :: (a -> Either b c) -> Encode b -> Encode c -> Encode a

Semigroup (Encode a)

Defined in Data.Sv.Encode.Type

Methods

(<>) :: Encode a -> Encode a -> Encode a

sconcat :: NonEmpty (Encode a) -> Encode a

stimes :: Integral b => b -> Encode a -> Encode a

Monoid (Encode a)

Defined in Data.Sv.Encode.Type

Methods

mempty :: Encode a

mappend :: Encode a -> Encode a -> Encode a

mconcat :: [Encode a] -> Encode a

Convenience constructors

mkEncodeBS :: (a -> ByteString) -> Encode a

Make an Encode from a function that builds one Field.

mkEncodeWithOpts :: (EncodeOptions -> a -> Builder) -> Encode a

Make an Encode from a function that builds one Field.

Running an Encode

encode :: Encode a -> EncodeOptions -> [a] -> ByteString

Encode the given list using the given Encode, configured by the given EncodeOptions.

encodeNamed :: NameEncode a -> EncodeOptions -> [a] -> ByteString

Encode the given list with a header using the given NameEncode, configured by the given EncodeOptions.

encodeToHandle :: Encode a -> EncodeOptions -> [a] -> Handle -> IO ()

Encode, writing the output to a file handle.

encodeNamedToHandle :: NameEncode a -> EncodeOptions -> [a] -> Handle -> IO ()

Encode with a header, writing the output to a file handle.

encodeToFile :: Encode a -> EncodeOptions -> [a] -> FilePath -> IO ()

Encode, writing to a file. This way is more efficient than encoding to a ByteString and then writing to file.

encodeNamedToFile :: NameEncode a -> EncodeOptions -> [a] -> FilePath -> IO ()

Encode with a header, writing to a file. This way is more efficient than encoding to a ByteString and then writing to file.

encodeBuilder :: Encode a -> EncodeOptions -> [a] -> Builder

Encode to a ByteString Builder, which is useful if you are going to combine the output with other ByteStrings.

encodeNamedBuilder :: NameEncode a -> EncodeOptions -> [a] -> Builder

Encode with column names to a ByteString Builder, which is useful if you are going to combine the output with other ByteStrings.

encodeRow :: Encode a -> EncodeOptions -> a -> ByteString

Encode one row only

encodeRowBuilder :: Encode a -> EncodeOptions -> a -> Builder

Encode one row only, as a ByteString Builder

Options

class HasSeparator c where

Classy lens for Separator

Methods

separator :: Lens' c Separator

Instances

HasSeparator Word8

Defined in Data.Sv.Structure.Separator

Methods

separator :: Lens' Word8 Separator

HasSeparator EncodeOptions

Defined in Data.Sv.Encode.Options

Methods

separator :: Lens' EncodeOptions Separator

class HasSeparator c => HasEncodeOptions c

Classy lenses for EncodeOptions

import Control.Lens

defaultEncodeOptions & newline .~ crlf & quoting .~ Always

Minimal complete definition

encodeOptions

Instances

HasEncodeOptions EncodeOptions

Defined in Data.Sv.Encode.Options

Methods

encodeOptions :: Lens' EncodeOptions EncodeOptions

quoting :: Lens' EncodeOptions Quoting

newline :: Lens' EncodeOptions Newline

terminalNewline :: Lens' EncodeOptions Bool

data EncodeOptions

These are options to configure encoding. A default is provided as defaultEncodeOptions.

Constructors

EncodeOptions

Fields

• _encodeSeparator :: Separator

  Are your values separated by commas, tabs, or something else? Default: comma

• _quoting :: Quoting

  Would you like quotes around your values? If so, double quotes or single? Deafult: Double quotes

• _newline :: Newline

  What kind of newline would you like? Default: LF

• _terminalNewline :: Bool

  Should the file be terminated with a newline? Default: No

Instances

HasSeparator EncodeOptions

Defined in Data.Sv.Encode.Options

Methods

separator :: Lens' EncodeOptions Separator

HasEncodeOptions EncodeOptions

Defined in Data.Sv.Encode.Options

Methods

encodeOptions :: Lens' EncodeOptions EncodeOptions

quoting :: Lens' EncodeOptions Quoting

newline :: Lens' EncodeOptions Newline

terminalNewline :: Lens' EncodeOptions Bool

data Quoting

Should the output file have quotes around every value, or only when they are required?

Beware the Never constructor. It can construct malformed CSV files if there are fields containing quotes, newlines, or separators. It is the fastest option though, so you might like to use it if you're sure none of your encoded data will include those characters.

Constructors

Always

AsNeeded

Never

defaultEncodeOptions :: EncodeOptions

The default options for encoding.

The default is a CSV file with quotes when necessary, LF lines, and no terminating newline.

Primitive encodes

Name-based

named :: Builder -> Encode a -> NameEncode a

Attach a column name to an Encode. This is used for building Encodes with headers.

Best used with OverloadedStrings

(=:) :: Builder -> Encode a -> NameEncode a

Synonym for named.

Mnemonic: Dot colon names Decoders, Equal colon names Encoders.

Field-based

const :: ByteString -> Encode a

Encode this ByteString every time, ignoring the input.

show :: Show a => Encode a

Build an Encode using a type's Show instance.

nop :: Encode a

Don't encode anything.

empty :: Encode a

Encode anything as the empty string.

orEmpty :: Encode a -> Encode (Maybe a)

Lift an Encode to be able to hanlde Maybe, by using the empty string in the case of Nothing

char :: Encode Char

Encode a single Char

int :: Encode Int

Encode an Int

integer :: Encode Integer

Encode an Integer

float :: Encode Float

Encode a Float

double :: Encode Double

Encode a Double

boolTrueFalse :: Encode Bool

Encode a Bool as True or False

booltruefalse :: Encode Bool

Encode a Bool as true of false

boolyesno :: Encode Bool

Encode a Bool as yes or no

boolYesNo :: Encode Bool

Encode a Bool as Yes or No

boolYN :: Encode Bool

Encode a Bool as Y or N

bool10 :: Encode Bool

Encode a Bool as 1 or 0

string :: Encode String

Encode a String

text :: Encode Text

Encode a Text

byteString :: Encode ByteString

Encode a strict ByteString

lazyByteString :: Encode ByteString

Encode a lazy ByteString

Row-based

row :: Encode s -> Encode [s]

Encode a list as a whole row at once, using the same Encode for every element

Combinators

(?>) :: Encode a -> Encode () -> Encode (Maybe a)

Build an Encode for Maybe given a Just and a Nothing encode.

(<?) :: Encode () -> Encode a -> Encode (Maybe a)

Build an Encode for Maybe given a Nothing and a Just encode.

(?>>) :: Encode a -> ByteString -> Encode (Maybe a)

Build an Encode for Maybe given a Just encode and a ByteString for the Nothing case.

(<<?) :: ByteString -> Encode a -> Encode (Maybe a)

Build an Encode for Maybe given a ByteString for the Nothing case and a Just encode.

encodeOf :: Getting (First a) s a -> Encode a -> Encode s

Given an optic from s to a, Try to use it to build an encode.

encodeOf :: Iso'       s a -> Encode a -> Encode s
encodeOf :: Lens'      s a -> Encode a -> Encode s
encodeOf :: Prism'     s a -> Encode a -> Encode s
encodeOf :: Traversal' s a -> Encode a -> Encode s
encodeOf :: Fold       s a -> Encode a -> Encode s
encodeOf :: Getter     s a -> Encode a -> Encode s

This is very useful when you have a prism for each constructor of your type. You can define an Encode as follows:

myEitherEncode :: Encode a -> Encode b -> Encode (Either a b)
myEitherEncode encA encB = encodeOf _Left encA <> encodeOf _Right encB

In this example, when the prism lookup returns Nothing, the empty encoder is returned. This is the mempty for the Encode monoid, so it won't add a field to the resulting CSV. This is the behaviour you want for combining a collection of prisms.

But this encoder also works with lenses (or weaker optics), which will never fail their lookup, in which case it never returns mempty. So this actually does the right thing for both sum and product types.

encodeOfMay :: Getting (First a) s a -> Encode (Maybe a) -> Encode s

Like encodeOf, but you can handle Nothing however you'd like. In encodeOf, it is handled by the Encode which does nothing, but for example you might like to use orEmpty to encode an empty field.

Unsafe encodes

unsafeBuilder :: (a -> Builder) -> Encode a

Make an encode from any function that returns a ByteString Builder.

unsafeString :: Encode String

Encode a String really quickly. If the string has quotes in it, they will not be escaped properly, so the result maybe not be valid CSV

unsafeText :: Encode Text

Encode Text really quickly. If the text has quotes in it, they will not be escaped properly, so the result maybe not be valid CSV

unsafeByteString :: Encode ByteString

Encode a ByteString really quickly. If the string has quotes in it, they will not be escaped properly, so the result maybe not be valid CSV

unsafeLazyByteString :: Encode ByteString

Encode a ByteString really quickly. If the string has quotes in it, they will not be escaped properly, so the result maybe not be valid CSV

unsafeByteStringBuilder :: Encode Builder

Encode ByteString Builder really quickly. If the builder builds a string with quotes in it, they will not be escaped properly, so the result maybe not be valid CSV

unsafeConst :: ByteString -> Encode a

Encode this ByteString really quickly every time, ignoring the input. If the string has quotes in it, they will not be escaped properly, so the result maybe not be valid CSV