Comparison operators

2 files changed, 151 insertions, 79 deletions

diff --git a/gen/list.erl b/gen/list.erl
index 662b283..cf76f31 100644
--- a/gen/list.erl
+++ b/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, map/2, do_traverse/3, traverse/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, do_traverse/3, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, foldl/3, foldr/3]).
 
 length(A) ->
     erlang:length(A).
@@ -80,6 +80,33 @@ tail_test() ->
     expect:equal(tail([]), {error, empty}).
 -endif.
 
+do_filter(List, Fun, Acc) ->
+    case List of
+        [] ->
+            reverse(Acc);
+
+        [X | Xs] ->
+            NewAcc = case Fun(X) of
+                true ->
+                    [X | Acc];
+
+                false ->
+                    Acc
+            end,
+            do_filter(Xs, Fun, NewAcc)
+    end.
+
+filter(List, Fun) ->
+    do_filter(List, Fun, []).
+
+-ifdef(TEST).
+filter_test() ->
+    expect:equal(filter([], fun(X) -> true end), []),
+    expect:equal(filter([0, 4, 5, 7, 3], fun(X) -> true end), [0, 4, 5, 7, 3]),
+    expect:equal(filter([0, 4, 5, 7, 3], fun(X) -> X > 4 end), [5, 7]),
+    expect:equal(filter([0, 4, 5, 7, 3], fun(X) -> X < 4 end), [0, 3]).
+-endif.
+
 do_map(List, Fun, Acc) ->
     case List of
         [] ->
@@ -129,6 +156,51 @@ traverse_test() ->
     expect:equal(traverse([4, 6, 5, 7, 3], Fun), {error, 7}).
 -endif.
 
+drop(List, N) ->
+    case N =< 0 of
+        true ->
+            List;
+
+        false ->
+            case List of
+                [] ->
+                    [];
+
+                [X | Xs] ->
+                    drop(Xs, N - 1)
+            end
+    end.
+
+-ifdef(TEST).
+drop_test() ->
+    expect:equal(drop([], 5), []),
+    expect:equal(drop([1, 2, 3, 4, 5, 6, 7, 8], 5), [6, 7, 8]).
+-endif.
+
+do_take(List, N, Acc) ->
+    case N =< 0 of
+        true ->
+            reverse(Acc);
+
+        false ->
+            case List of
+                [] ->
+                    reverse(Acc);
+
+                [X | Xs] ->
+                    do_take(Xs, N - 1, [X | Acc])
+            end
+    end.
+
+take(List, N) ->
+    do_take(List, N, []).
+
+-ifdef(TEST).
+take_test() ->
+    expect:equal(take([], 5), []),
+    expect:equal(take([1, 2, 3, 4, 5, 6, 7, 8], 5), [1, 2, 3, 4, 5]).
+-endif.
+
 new() ->
     [].
 
diff --git a/src/list.gleam b/src/list.gleam
index 3f79b52..e0a8f42 100644
--- a/src/list.gleam
+++ b/src/list.gleam
@@ -78,40 +78,40 @@ test tail {
     |> expect:equal(_, Error(Empty))
 }
 
-// fn do_filter(list, fun, acc) {
-//   case list {
-//   | [] -> reverse(acc)
-//   | [x | xs] ->
-//       let new_acc =
-//         case fun(x) {
-//         | True -> [x | acc]
-//         | False -> acc
-//         }
-//       do_filter(xs, fun, new_acc)
-//   }
-// }
-
-// pub fn filter(list, fun) {
-//   do_filter(list, fun, [])
-// }
-
-// test filter {
-//   []
-//     |> filter(_, fn(x) { True })
-//     |> expect:equal(_, [])
-
-//   [0, 4, 5, 7, 3]
-//     |> filter(_, fn(x) { True })
-//     |> expect:equal(_, [0, 4, 5, 7, 3])
-
-//   [0, 4, 5, 7, 3]
-//     |> filter(_, fn(x) { x > 4 })
-//     |> expect:equal(_, [5, 7])
-
-//   [0, 4, 5, 7, 3]
-//     |> filter(_, fn(x) { x < 4 })
-//     |> expect:equal(_, [0, 3])
-// }
+fn do_filter(list, fun, acc) {
+  case list {
+  | [] -> reverse(acc)
+  | [x | xs] ->
+      let new_acc =
+        case fun(x) {
+        | True -> [x | acc]
+        | False -> acc
+        }
+      do_filter(xs, fun, new_acc)
+  }
+}
+
+pub fn filter(list, fun) {
+  do_filter(list, fun, [])
+}
+
+test filter {
+  []
+    |> filter(_, fn(x) { True })
+    |> expect:equal(_, [])
+
+  [0, 4, 5, 7, 3]
+    |> filter(_, fn(x) { True })
+    |> expect:equal(_, [0, 4, 5, 7, 3])
+
+  [0, 4, 5, 7, 3]
+    |> filter(_, fn(x) { x > 4 })
+    |> expect:equal(_, [5, 7])
+
+  [0, 4, 5, 7, 3]
+    |> filter(_, fn(x) { x < 4 })
+    |> expect:equal(_, [0, 3])
+}
 
 fn do_map(list, fun, acc) {
   case list {
@@ -167,50 +167,50 @@ test traverse {
 }
 
 
-// pub fn drop(list, n) {
-//   case n <= 0 {
-//   | True -> list
-//   | False ->
-//       case list {
-//       | [] -> []
-//       | [x | xs] -> drop(xs, n - 1)
-//       }
-//   }
-// }
-
-// test drop {
-//   []
-//     |> drop(_, 5)
-//     |> expect:equal(_, [])
-
-//   [1, 2, 3, 4, 5, 6, 7, 8]
-//     |> drop(_, 5)
-//     |> expect:equal(_, [6, 7, 8])
-// }
-
-// fn do_take(list, n, acc) {
-//   case n <= 0 {
-//   | True -> reverse(acc)
-//   | False ->
-//       case list {
-//       | [] -> reverse(acc)
-//       | [x | xs] -> take(xs, n - 1, [x | acc])
-//       }
-//   }
-// }
-
-// pub fn take(list, n) {
-//   do_take(list, n, [])
-// }
-
-// test take {
-//   []
-//     |> take(_, 5)
-//     |> expect:equal(_, [])
-//   [1, 2, 3, 4, 5, 6, 7, 8]
-//     |> take(_, 5)
-//     |> expect:equal(_, [1, 2, 3, 4, 5])
-// }
+pub fn drop(list, n) {
+  case n <= 0 {
+  | True -> list
+  | False ->
+      case list {
+      | [] -> []
+      | [x | xs] -> drop(xs, n - 1)
+      }
+  }
+}
+
+test drop {
+  []
+    |> drop(_, 5)
+    |> expect:equal(_, [])
+
+  [1, 2, 3, 4, 5, 6, 7, 8]
+    |> drop(_, 5)
+    |> expect:equal(_, [6, 7, 8])
+}
+
+fn do_take(list, n, acc) {
+  case n <= 0 {
+  | True -> reverse(acc)
+  | False ->
+      case list {
+      | [] -> reverse(acc)
+      | [x | xs] -> do_take(xs, n - 1, [x | acc])
+      }
+  }
+}
+
+pub fn take(list, n) {
+  do_take(list, n, [])
+}
+
+test take {
+  []
+    |> take(_, 5)
+    |> expect:equal(_, [])
+  [1, 2, 3, 4, 5, 6, 7, 8]
+    |> take(_, 5)
+    |> expect:equal(_, [1, 2, 3, 4, 5])
+}
 
 pub fn new() {
   []