Tuple

Dark v1 does not have tuples. Dark v1 allowed different types in the same list, though, which was not a great experience as the rest of the language mostly expected the language to be typed.

Goals

Tuples are useful for situations where you want to group information together but do:

• do not want a full blown record
• want heterogeneous types
• want destructuring

V2 definition

type Expr =
  | ETuple { exprs : List Expr }
  | ...

type Pattern =
  | PTuple { pats : List Pattern }
  | ...

type Dval =
  | DTuple { vals = List Dval }
  | ...

type DType =
  | TTuple { contents = List DTyple }
  | ...

Interaction model

let (myString, myInt) = ("str", 6)

Creation:

'let ' =>
  let |___ = ___
( =>
  let (|) = ___
myString =>
  let (myString|) = ___
, =>
  let (myString, |___) = ___
'myInt) = ' =>
  let (myString, myInt) = |___
( =>
  let (myString, myInt) = (|)
'"str", ' =>
  let (myString, myInt) = ("str", |___)
5) =>
  let (myString, myInt) = ("str", 5)|

Standard library

// Access
Tuple2::first ('a,'b) -> 'a
Tuple2::second ('a,'b) -> 'b

// Creation
Tuple2::pair ('a, 'b) -> ('a,'b)

// Manipulation
Tuple2::mapFirst (('a,'b), ('a -> 'c)) -> ('c, 'b)
Tuple2::mapSecond (('a,'b), ('b -> 'c)) -> ('b, 'c)
Tuple2::mapBoth (('a,'b), ('a -> 'c), ('b -> 'd)) -> ('c, 'd)

Tuple2::swap (('a,'b)) -> ('b, 'a)


// And all the equivalents for Tuple3
// Also possibly bonus functions from https://package.elm-lang.org/packages/TSFoster/elm-tuple-extra/latest/Tuple3

Changes in existing libraries:

List.zip_v1(List 'a, List 'b) -> Option (List ('a, 'b))
List.zipShortest_v1(List 'a, List 'b) -> List ('a, 'b)
List.unzip_v1(List ('a, 'b) -> (List 'a, List 'b)

Dict.fromList_v1(List ('a, 'b)) -> Option (Dict 'a 'b)
Dict.fromListOverwritingDuplicates_v1(List ('a, 'b)) -> Dict 'a 'b
Dict.toList_v1(Dict 'a 'b) -> List ('a, 'b)

There should be some version of a HttpClient function that takes tuples, as it is legal to have multiple headers of the same type and so tuples rather than dicts represent the correct type. Since we expect users to use built-ins for headers (such as Http::jsonContentType), this seems doable soon.