ExEdn

edn (extensible data notation) encoder/decoder implemented in Elixir.

Usage

Include ExEdn as a dependency in your Elixir by adding it in your deps list:

def deps do
  [{:ex_edn, "~> 0.1.2"}]
end

Since ExEdn is not an OTP application there is no need to add it to the list of :applications in your mix.exs.

Examples

iex> ExEdn.encode([1, 2])
{:ok, "(1, 2)"}

iex> ExEdn.encode(%{a: 1, b: 2, c: 3})
{:ok, "{:a 1, :b 2, :c 3}"}

iex> ExEdn.encode({:a, 1})
{:error, Protocol.UndefinedError}

iex> ExEdn.decode("{:a 1 :b 2}")
{:ok, %{a: 1, b: 2}}

iex> ExEdn.decode("(hello :world \\!)")
{:ok, [%ExEdn.Symbol{name: "hello"}, :world, %ExEdn.Character{char: "!"}]

iex> ExEdn.decode("[1 2 3 4]")
{:ok, #Array<[1, 2, 3, 4], fixed=false, default=nil>}

iex> ExEdn.decode("nil true false")
{:ok, #Array<[1, 2, 3, 4], fixed=false, default=nil>}

iex> ExEdn.decode("nil true false .")
{:error, ExEdn.Exception.UnexpectedInputError}

Data Structures Mapping: edn <-> Elixir

Further Considerations

Character

There is no way of distinguishing a common integer from the representation of a character in a String or in Char lists. This forces the creation of a new representation for this type so it can be correctly translated to from and to edn.

Arbitrary Precision Integer and Float

The Erlang VM (EVM) only provides arbitrary precision integer so all integers will have this and the N modifier will be ignored when present.

On the other hand native arbitrary precision floating point numbers are not provided by the EVM so all values of type float will be represented according to what the EVM supports.

Keyword and Symbol Representation

The decision to translate keywords as atoms on the EVM comes form the common use these two data type are given. It might get awkward really quickly using a new ExEdn.Symbol struct as the representation for edn's symbols so this might change.

vector

There is no constant lookup or nearly constant indexed data structure like edn's vector other than the :array data structure implemented in one of Erlang's standard library modules. Until there is a better implementation for this ExEdn will use the Array, an Elixir wrapper library for Erlang's array.

edn grammar

expr -> literal | map | list | vector | tagged_value

literal -> nil | true | false | keyword | symbol | integer | float | string

map -> { pair* }
pair -> expr expr

list -> ( expr* )

vector -> [ expr* ]

tagged_value -> tag expr