aeson-pretty-0.8.7: JSON pretty-printing library and command-line tool.

Data.Aeson.Encode.Pretty

Description

Aeson-compatible pretty-printing of JSON Values.

Synopsis

# Simple Pretty-Printing

encodePretty :: ToJSON a => a -> ByteString Source #

A drop-in replacement for aeson's encode function, producing JSON-ByteStrings for human readers.

Follows the default configuration in defConfig.

A drop-in replacement for aeson's encodeToTextBuilder function, producing JSON-ByteStrings for human readers.

Follows the default configuration in defConfig.

# Pretty-Printing with Configuration Options

encodePretty' :: ToJSON a => Config -> a -> ByteString Source #

A variant of encodePretty that takes an additional configuration parameter.

encodePrettyToTextBuilder' :: ToJSON a => Config -> a -> Builder Source #

A variant of encodeToTextBuilder that takes an additional configuration parameter.

data Config Source #

Constructors

 Config FieldsconfIndent :: IndentIndentation per level of nestingconfCompare :: Text -> Text -> OrderingFunction used to sort keys in objectsconfNumFormat :: NumberFormat confTrailingNewline :: BoolWhether to add a trailing newline to the output

The default configuration: indent by four spaces per level of nesting, do not sort objects by key, do not add trailing newline.

defConfig = Config { confIndent = Spaces 4, confCompare = mempty, confNumFormat = Generic, confTrailingNewline = False }

data Indent Source #

Indentation per level of nesting. Spaces 0 removes all whitespace from the output.

Constructors

 Spaces Int Tab

Constructors

 Generic The standard behaviour of the encode function. Uses integer literals for integers (1, 2, 3...), simple decimals for fractional values between 0.1 and 9,999,999, and scientific notation otherwise. Scientific Scientific notation (e.g. 2.3e123). Decimal Standard decimal notation Custom (Scientific -> Builder) Custom formatting function

## Sorting Keys in Objects

With the Aeson library, the order of keys in objects is undefined due to objects being implemented as HashMaps. To allow user-specified key orders in the pretty-printed JSON, encodePretty' can be configured with a comparison function. These comparison functions can be composed using the Monoid interface. Some other useful helper functions to keep in mind are comparing and on.

Consider the following deliberately convoluted example, demonstrating the use of comparison functions:

An object might pretty-print as follows

{
"baz": ...,
"bar": ...,
"foo": ...,
"quux": ...,
}

which is clearly a confusing order of keys. By using a comparison function such as

comp :: Text -> Text -> Ordering
comp = keyOrder ["foo","bar"] mappend comparing length

we can achieve the desired neat result:

{
"foo": ...,
"bar": ...,
"baz": ...,
"quux": ...,
}

mempty :: Monoid a => a #

Identity of mappend

Serves as an order-preserving (non-)sort function. Re-exported from Data.Monoid.

compare :: Ord a => a -> a -> Ordering #

Sort keys in their natural order, i.e. by comparing character codes. Re-exported from the Prelude and Data.Ord

keyOrder :: [Text] -> Text -> Text -> Ordering Source #

Sort keys by their order of appearance in the argument list.

Keys that are not present in the argument list are considered to be greater than any key in the list and equal to all keys not in the list. I.e. keys not in the argument list are moved to the end, while their order is preserved.