Elm Edn Parser

A library for parsing extensible data notation, "Edn" in Elm!

This is very useful for communicating between Clojure and Elm.

The "Edn" Type

type Edn
    = EdnString String
    | EdnSymbol String
    -- keywords are represented as strings with optional namespace
    | EdnKeyword (Maybe String) String
    | EdnList (List Edn)
    | EdnVector (Array Edn)
    -- maps in Edn can have keys that are not strings, so we represent them as a list
    -- of tuples here, leaving the translation to a map up to decoders
    | EdnMap (List ( Edn, Edn ))
    -- sets must consist of predefined comparables in Elm, so it's represented
    -- as a list on this type, leaving the translation to a set up to decoders
    | EdnSet (List Edn)
    | EdnNil
    | EdnBool Bool
    | EdnInt Int
    | EdnFloat Float
    | EdnChar Char
    -- user defined tags have a namespace and a name, followed by a nested edn value
    | EdnTag String String Edn
    | EdnSymbol String

Decoding/Encoding

This library doesn't provide Encoders and Decoders for the types in the Edn module.

Extensible Data Notation has a few interesting types that don't necessarily translate 1 to 1 without making some decisions about how that transform happens.

• Edn maps can have keys that are not strings. The EdnMap type in this library represents them as List (Edn, Edn).
• Edn has sets that can contain more than what Elm considers "comparable". The EdnSet type in this library represents them as List Edn.
• Tags are a cool feature of Edn that can instruct a client consuming the data how to handle that tagged data differently. There are a couple different possible ways a decoder library can represent this.

So there's several things about .edn that manifest as implementation details for decoder libraries to deal with. I plan to create a decoder/encode package to accompany this, but want to keep it separate in case anyone wants to write their own that handles things differently than I do.

Prior Art

The tests in this library and the escaped unicode parsing are largely drawn from Robert Vollmert's excellent elm-edn library.