purescript-undefined-or

A purescript library for more convenient interfacing with foreign code.

A lot of JS functions accept and return records where some fields may be missing. For missing fields in argument records you can use Data.Options module. For missing fields in return records you can either use Foreign and write parsers, or this module and trust the foreign code.

A simple example of usage:

// Test.js
exports.typicalApi = function() {
  if (Math.random() > 0.5) {
    return {"numberData": 9431, "stringData": "atad"};
  } else {
    return {"numberData": 8752}
  }
}

-- Test.purs
type ApiRet = {numberData :: Boolean, stringData :: UndefinedOr String}

foreign import typicalApi :: Effect ApiRet

...

result <- typicalApi
case fromUndefined result.stringData of
    Just data -> Console.log $ "got a string: " <> data
    Nothing   -> Console.log "no string"

You should avoid using this library whenever possible, as it's a shortcut: it lifts the neccessity of data validation from you, the ffi-bindings writer, to the user of your api. Also 75% of the use cases can be covered by clever use of typeclasses.