Config
- confIndent :: Indent
  Indentation per level of nesting
- confCompare :: Text -> Text -> Ordering
  Function used to sort keys in objects
- confNumFormat :: NumberFormat
- confTrailingNewline :: Bool
  Whether to add a trailing newline to the output

valuedefConfig :: Config

Source#

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 }

datadata Indent

Source#

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

Constructors

Spaces Int
Tab

datadata NumberFormat

Constructors

Generic
For numbers with absolute value less than 1e19, this follows 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. For numbers with an absolute value larger than 1e19, always uses scientific notation.
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": ...,
}

methodmempty :: a

Source#

Identity of mappend

Examples

Example1 expression

>>> "Hello world" <> mempty"Hello world"

Example1 expression

>>> mempty <> [1, 2, 3][1,2,3]

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

methodcompare :: a -> a -> Ordering

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

valuekeyOrder :: [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.