1cat = { git = "https://github.com/VSebastian8/cat.git", ref = "main" }

 1import cat.{type Either, Left, Right}
 2import cat/applicative as app
 3import cat/bifunctor as bf
 4import cat/functor.{functor_compose}
 5import cat/instances/applicative as appi
 6import cat/instances/bifunctor as bfi
 7import cat/instances/functor as funi
 8import cat/instances/monad.{Reader, Writer, fish, reader_return, writer_return}
 9import cat/instances/monoid as moni
10import cat/monoid.{type Monoid, Monoid, mconcat}
11import gleam/int
12import gleam/option.{None, Some}
13import gleam/string
14
15pub fn main() {
16  // Monoid example from README (somewhat adapted).
17  let either_sum_monoid =
18    Monoid(
19      mempty: Left(0),
20      mappend: fn(e1: Either(Int, String), e2: Either(Int, String)) -> Either(
21        Int,
22        String,
23      ) {
24        case e1, e2 {
25          Right(s), _ -> Right(s)
26          _, Right(s) -> Right(s)
27          Left(a), Left(b) -> Left(a + b)
28        }
29      },
30    )
31
32  either_sum_monoid
33  |> mconcat([Left(2), Left(3), Left(4)])
34  |> echo
35  echo " ---> Left(9)"
36
37  either_sum_monoid
38  |> mconcat([Left(2), Right("error"), Left(4)])
39  |> echo
40  echo " ---> Right(\"error\")"
41  
42  // Functor example from README (somewhat adapted).
43  option.Some([1, 2, 3])
44  |> functor_compose(funi.option_functor(), funi.list_functor()).fmap(fn(x) {
45    x % 2 == 0
46  })
47  |> echo
48  echo " ---> Some([False, True, False])"
49
50  // Applicative example from README (somewhat adapted).
51  [Some(1), None, Some(3)]
52  |> {
53    [fn(x) { x * 2 }, fn(x) { x + 10 }]
54    |> funi.list_functor().fmap(funi.option_functor().fmap)
55    |> app.apply(appi.list_applicative())
56  }
57  |> echo
58  echo " ---> [Some(2), None, Some(6), Some(11), None, Some(13)"
59
60  // Bifunctor examples from README (somewhat adapted)
61  // Either bifunctor
62  let either_bf = bfi.either_bifunctor()
63  // Const () functor
64  let const_f = funi.const_functor()
65  // Identity functor
66  let id_f = funi.identity_functor()
67
68  // Constructing the maybe functor:
69  // Maybe b = Either (Const () a) (Identity b)
70  let maybe_functor = fn() -> bf.Bifunctor(
71    bf.BiCompF(bfi.EitherBF, funi.ConstF(Nil), funi.IdentityF),
72    a,
73    b,
74    c,
75    d,
76    cat.Either(cat.Const(Nil, a), cat.Identity(b)),
77    cat.Either(cat.Const(Nil, c), cat.Identity(d)),
78  ) {
79    bf.bifunctor_compose(either_bf, const_f, id_f)
80  }
81
82  cat.Left(cat.Const(Nil))
83  |> maybe_functor().bimap(fn(_) { panic }, int.to_string)
84  |> echo
85  echo " ---> Left(Const(Nil)"
86
87  cat.Right(cat.Identity(3))
88  |> maybe_functor().bimap(fn(_) { panic }, int.to_string)
89  |> echo
90  echo " ---> Right(Identity(\"3\")"
91}