list:split_while

Author: bsnyder788

CHANGELOG.md

@@ -5,7 +5,7 @@
 - The `map_dict` module gains `update`, `merge` and `delete` functions.
 - The `bool` module gains a `compare` function.
 - The `int` module gains a `compare` function.
-- The `list` module gains `range`, `repeat`, `split`, and `strict_zip` functions.
+- The `list` module gains `range`, `repeat`, `split`, `split_while` and `strict_zip` functions.
 
 ## v0.1.2 - 2019-04-25
 

gen/src/list.erl

@@ -1,7 +1,7 @@
 -module(list).
 -compile(no_auto_import).
 
--export([length/1, reverse/1, is_empty/1, contains/2, head/1, tail/1, filter/2, map/2, index_map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, fold/3, fold_right/3, find/2, all/2, any/2, zip/2, strict_zip/2, intersperse/2, at/2, unique/1, sort/1, range/2, repeat/2, split/2]).
+-export([length/1, reverse/1, is_empty/1, contains/2, head/1, tail/1, filter/2, map/2, index_map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, fold/3, fold_right/3, find/2, all/2, any/2, zip/2, strict_zip/2, intersperse/2, at/2, unique/1, sort/1, range/2, repeat/2, split/2, split_while/2]).
 
 length(A) ->
     erlang:length(A).
@@ -349,3 +349,21 @@ do_split(List, N, Taken) ->
 
 split(List, N) ->
     do_split(List, N, []).
+
+do_split_while(List, F, Acc) ->
+    case List of
+        [] ->
+            {reverse(Acc), []};
+
+        [X | Xs] ->
+            case F(X) of
+                false ->
+                    {reverse(Acc), List};
+
+                _ ->
+                    do_split_while(Xs, F, [X | Acc])
+            end
+    end.
+
+split_while(List, F) ->
+    do_split_while(List, F, []).

gen/test/list_test.erl

@@ -1,7 +1,7 @@
 -module(list_test).
 -compile(no_auto_import).
 
--export([length_test/0, reverse_test/0, is_empty_test/0, contains_test/0, head_test/0, tail_test/0, filter_test/0, map_test/0, traverse_test/0, drop_test/0, take_test/0, new_test/0, append_test/0, flatten_test/0, fold_test/0, fold_right_test/0, find_test/0, all_test/0, any_test/0, zip_test/0, strict_zip_test/0, intersperse_test/0, at_test/0, unique_test/0, sort_test/0, index_map_test/0, range_test/0, repeat_test/0, split_test/0]).
+-export([length_test/0, reverse_test/0, is_empty_test/0, contains_test/0, head_test/0, tail_test/0, filter_test/0, map_test/0, traverse_test/0, drop_test/0, take_test/0, new_test/0, append_test/0, flatten_test/0, fold_test/0, fold_right_test/0, find_test/0, all_test/0, any_test/0, zip_test/0, strict_zip_test/0, intersperse_test/0, at_test/0, unique_test/0, sort_test/0, index_map_test/0, range_test/0, repeat_test/0, split_test/0, split_while_test/0]).
 
 length_test() ->
     expect:equal(list:length([]), 0),
@@ -170,3 +170,14 @@ split_test() ->
     expect:equal(list:split([0, 1, 2, 3, 4], 1), {[0], [1, 2, 3, 4]}),
     expect:equal(list:split([0, 1, 2, 3, 4], 3), {[0, 1, 2], [3, 4]}),
     expect:equal(list:split([0, 1, 2, 3, 4], 9), {[0, 1, 2, 3, 4], []}).
+
+split_while_test() ->
+    expect:equal(list:split_while([], fun(X) -> X =< 5 end), {[], []}),
+    expect:equal(list:split_while([1, 2, 3, 4, 5], fun(X) -> X =< 5 end),
+                 {[1, 2, 3, 4, 5], []}),
+    expect:equal(list:split_while([1, 2, 3, 4, 5], fun(X) -> X =:= 2 end),
+                 {[], [1, 2, 3, 4, 5]}),
+    expect:equal(list:split_while([1, 2, 3, 4, 5], fun(X) -> X =< 3 end),
+                 {[1, 2, 3], [4, 5]}),
+    expect:equal(list:split_while([1, 2, 3, 4, 5], fun(X) -> X =< -3 end),
+                 {[], [1, 2, 3, 4, 5]}).

src/list.gleam

@@ -289,3 +289,18 @@ fn do_split(list, n, taken) {
 pub fn split(list, n) {
   do_split(list, n, [])
 }
+
+fn do_split_while(list, f, acc) {
+  case list {
+    | [] -> {reverse(acc), []}
+    | [x | xs] -> 
+      case f(x) {
+      | False -> {reverse(acc), list}
+      | _ -> do_split_while(xs, f, [x | acc])
+      }
+  }
+}
+
+pub fn split_while(list, f) {
+  do_split_while(list, f, [])
+}

test/list_test.gleam

@@ -332,3 +332,20 @@ pub fn split_test() {
   list:split([0, 1, 2, 3, 4], 9)
   |> expect:equal(_, {[0, 1, 2, 3, 4], []})
 }
+
+pub fn split_while_test() {
+  list:split_while([], fn(x) { x <= 5 })
+  |> expect:equal(_, {[], []})
+
+  list:split_while([1, 2, 3, 4, 5], fn(x) { x <= 5 })
+  |> expect:equal(_, {[1, 2, 3, 4, 5], []})
+
+  list:split_while([1, 2, 3, 4, 5], fn(x) { x == 2 })
+  |> expect:equal(_, {[], [1, 2, 3, 4, 5]})
+
+  list:split_while([1, 2, 3, 4, 5], fn(x) { x <= 3 })
+  |> expect:equal(_, {[1, 2, 3], [4, 5]})
+
+  list:split_while([1, 2, 3, 4, 5], fn(x) { x <= -3 })
+  |> expect:equal(_, {[], [1, 2, 3, 4, 5]})
+}