stdlib additions

Author: lpil

gen/list.erl

@@ -2,7 +2,7 @@
 -compile(no_auto_import).
 -include_lib("eunit/include/eunit.hrl").
 
--export([length/1, reverse/1, is_empty/1, has_member/2, head/1, tail/1, filter/2, map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, foldl/3, foldr/3]).
+-export([length/1, reverse/1, is_empty/1, has_member/2, head/1, tail/1, filter/2, map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, foldl/3, foldr/3, find/2]).
 
 length(A) ->
     erlang:length(A).
@@ -264,3 +264,32 @@ foldr(List, Acc, Fun) ->
 foldr_test() ->
     expect:equal(foldr([1, 2, 3], [], fun(X, Acc) -> [X | Acc] end), [1, 2, 3]).
 -endif.
+
+find(Haystack, F) ->
+    case Haystack of
+        [] ->
+            {error, not_found};
+
+        [X | Rest] ->
+            case F(X) of
+                {ok, X1} ->
+                    {ok, X1};
+
+                _ ->
+                    find(Rest, F)
+            end
+    end.
+
+-ifdef(TEST).
+find_test() ->
+    F = fun(X) -> case X of
+            2 ->
+                {ok, 4};
+
+            _ ->
+                {error, not_found}
+        end end,
+    expect:equal(find([1, 2, 3], F), {ok, 4}),
+    expect:equal(find([1, 3, 2], F), {ok, 4}),
+    expect:equal(find([1, 3], F), {error, not_found}).
+-endif.

gen/tuple.erl

@@ -2,7 +2,16 @@
 -compile(no_auto_import).
 -include_lib("eunit/include/eunit.hrl").
 
--export([first/1, second/1]).
+-export([new/2, first/1, second/1, swap/1, fetch/2]).
+
+new(A, B) ->
+    {A, B}.
+
+-ifdef(TEST).
+new_test() ->
+    expect:equal(new(1, 2), {1, 2}),
+    expect:equal(new(2, <<"3">>), {2, <<"3">>}).
+-endif.
 
 first(Tup) ->
     {A, _} = Tup,
@@ -21,3 +30,29 @@ second(Tup) ->
 second_test() ->
     expect:equal(second({1, 2}), 2).
 -endif.
+
+swap(Tup) ->
+    {A, B} = Tup,
+    {B, A}.
+
+-ifdef(TEST).
+swap_test() ->
+    expect:equal(swap({1, <<"2">>}), {<<"2">>, 1}).
+-endif.
+
+fetch(Haystack, Needle) ->
+    list:find(Haystack, fun(Tuple) -> case first(Tuple) =:= Needle of
+                      true ->
+                          {ok, second(Tuple)};
+
+                      false ->
+                          {error, []}
+                  end end).
+
+-ifdef(TEST).
+fetch_test() ->
+    Proplist = [{0, <<"1">>}, {1, <<"2">>}],
+    expect:equal(fetch(Proplist, 0), {ok, <<"1">>}),
+    expect:equal(fetch(Proplist, 1), {ok, <<"2">>}),
+    expect:is_error(fetch(Proplist, 2)).
+-endif.

src/list.gleam

@@ -3,6 +3,9 @@ import expect
 pub enum Empty =
   | Empty
 
+pub enum NotFound =
+  | NotFound
+
 // Using the Erlang C BIF implementation.
 //
 pub external fn length(List(a)) -> Int = "erlang" "length"
@@ -279,3 +282,35 @@ test foldr {
     |> foldr(_, [], fn(x, acc) { [x | acc] })
     |> expect:equal(_, [1, 2, 3])
 }
+
+pub fn find(haystack, f) {
+  case haystack {
+  | [] -> Error(NotFound)
+  | [x | rest] ->
+      case f(x) {
+      | Ok(x) -> Ok(x)
+      | _ -> find(rest, f)
+      }
+  }
+}
+
+test find {
+  let f = fn(x) {
+    case x {
+    | 2 -> Ok(4)
+    | _ -> Error(NotFound)
+    }
+  }
+
+  [1, 2, 3]
+  |> find(_, f)
+  |> expect:equal(_, Ok(4))
+
+  [1, 3, 2]
+  |> find(_, f)
+  |> expect:equal(_, Ok(4))
+
+  [1, 3]
+  |> find(_, f)
+  |> expect:equal(_, Error(NotFound))
+}

src/tuple.gleam

@@ -1,4 +1,18 @@
 import expect
+import result
+import list
+
+pub fn new(a, b) {
+  {a, b}
+}
+
+test new {
+  new(1, 2)
+  |> expect:equal(_, {1, 2})
+
+  new(2, "3")
+  |> expect:equal(_, {2, "3"})
+}
 
 pub fn first(tup) {
   let {a, _} = tup
@@ -21,3 +35,39 @@ test second {
   |> second
   |> expect:equal(_, 2)
 }
+
+pub fn swap(tup) {
+  let {a, b} = tup
+  {b, a}
+}
+
+test swap {
+  {1, "2"}
+  |> swap
+  |> expect:equal(_, {"2", 1})
+}
+
+pub fn fetch(haystack, needle) {
+  list:find(haystack, fn(tuple) {
+    case first(tuple) == needle {
+    | True -> Ok(second(tuple))
+    | False -> Error([])
+    }
+  })
+}
+
+test fetch {
+  let proplist = [{0, "1"}, {1, "2"}]
+
+  proplist
+  |> fetch(_, 0)
+  |> expect:equal(_, Ok("1"))
+
+  proplist
+  |> fetch(_, 1)
+  |> expect:equal(_, Ok("2"))
+
+  proplist
+  |> fetch(_, 2)
+  |> expect:is_error
+}