list.filter_map

5 files changed, 78 insertions, 21 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7926881..2ed6646 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - `uri` module created with `parse`, `parse_query`, `path_segments`,
   `query_to_string` and `to_string`.
 - The `dynamic` module gains the `tuple2`, and `tuple2_of` functions.
+- The `list` module gains the `filter_map` function.
 
 ## v0.8.0 - 2020-04-28
 
diff --git a/src/gleam/gleam_uri_native.erl b/src/gleam/gleam_uri_native.erl
index 5d225cb..dafd406 100644
--- a/src/gleam/gleam_uri_native.erl
+++ b/src/gleam/gleam_uri_native.erl
@@ -1,5 +1,5 @@
 -module (gleam_uri_native).
--export ([parse/1, to_string/1, parse_query/1]).
+-export ([parse/1]).
 
 find_key(Key, Map) ->
   case maps:find(Key, Map) of
@@ -25,21 +25,3 @@ parse(String) ->
         find_key(fragment, Map)
       }}
   end.
-
-to_string({uri, MaybeScheme, MaybeUserinfo, MaybeHost, MaybePort, Path, MaybeQuery, MaybeFragment}) ->
-  Components = [{scheme, MaybeScheme}, {userinfo, MaybeUserinfo}, {host, MaybeHost}, {port, MaybePort}, {path, {ok, Path}}, {query, MaybeQuery}, {fragment, MaybeFragment}],
-  Map = maps:from_list([{K, V} || {K, {ok, V}} <- Components]),
-  case uri_string:recompose(Map) of
-    String when is_binary(String) ->
-      String;
-    % Return value when empty
-    [] -> <<"">>
-  end.
-
-parse_query(String) ->
-  case uri_string:dissect_query(String) of
-    {error, _Reason, _Term} ->
-      {error, nil};
-    Parts ->
-      {ok, Parts}
-    end.
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index a0098a1..4e10c15 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -196,6 +196,38 @@ pub fn filter(list: List(a), for predicate: fn(a) -> Bool) -> List(a) {
   do_filter(list, predicate, [])
 }
 
+fn do_filter_map(
+  list: List(a),
+  fun: fn(a) -> Result(b, e),
+  acc: List(b),
+) -> List(b) {
+  case list {
+    [] -> reverse(acc)
+    [x, ..xs] -> {
+      let new_acc = case fun(x) {
+        Ok(x) -> [x, ..acc]
+        Error(_) -> acc
+      }
+      do_filter_map(xs, fun, new_acc)
+    }
+  }
+}
+
+/// Returns a new list containing only the elements from the first list for
+/// which the given functions returns `True`.
+///
+/// ## Examples
+///
+///    > filter_map([2, 4, 6, 1], Error)
+///    []
+///
+///    > filter_map([2, 4, 6, 1], fn(x) { Ok(x + 1) })
+///    [3, 4, 6, 2]
+///
+pub fn filter_map(list: List(a), with fun: fn(a) -> Result(b, e)) -> List(b) {
+  do_filter_map(list, fun, [])
+}
+
 fn do_map(list: List(a), fun: fn(a) -> b, acc: List(b)) -> List(b) {
   case list {
     [] -> reverse(acc)
diff --git a/src/gleam/uri.gleam b/src/gleam/uri.gleam
index 8536d98..a62cf3c 100644
--- a/src/gleam/uri.gleam
+++ b/src/gleam/uri.gleam
@@ -11,6 +11,7 @@ import gleam/list
 import gleam/result.{Option}
 import gleam/string
 import gleam/dynamic.{Dynamic}
+import gleam/map.{Map}
 
 /// Type representing holding the parsed components of an URI.
 /// All components of a URI are optional, except the path.
@@ -100,9 +101,40 @@ pub fn path_segments(path) {
   do_path_segments(string.split(path, "/"), [])
 }
 
+type UriKey {
+  Scheme
+  Userinfo
+  Host
+  Port
+  Path
+  Query
+  Fragment
+}
+
+external fn erl_to_string(Map(UriKey, Dynamic)) -> Dynamic =
+  "uri_string" "recompose"
+
 /// Encode a `Uri` value as a URI string.
 ///
 /// The opposite operation is `uri.parse`.
 ///
-pub external fn to_string(Uri) -> String =
-  "gleam_uri_native" "to_string"
+pub fn to_string(uri: Uri) -> String {
+  let field = fn(key: UriKey, value: Option(anything)) {
+    result.map(value, fn(value) { tuple(key, dynamic.from(value)) })
+  }
+
+  [
+    field(Scheme, uri.scheme),
+    field(Userinfo, uri.userinfo),
+    field(Host, uri.host),
+    field(Port, uri.port),
+    field(Path, Ok(uri.path)),
+    field(Query, uri.query),
+    field(Fragment, uri.fragment),
+  ]
+  |> list.filter_map(fn(x) { x })
+  |> map.from_list
+  |> erl_to_string
+  |> dynamic.string
+  |> result.unwrap("")
+}
diff --git a/test/gleam/list_test.gleam b/test/gleam/list_test.gleam
index 1be4e43..4576d7f 100644
--- a/test/gleam/list_test.gleam
+++ b/test/gleam/list_test.gleam
@@ -79,6 +79,16 @@ pub fn filter_test() {
   |> should.equal([0, 3])
 }
 
+pub fn filter_map_test() {
+  [2, 4, 6, 1]
+  |> list.filter_map(fn(x) { Ok(x + 1) })
+  |> should.equal([3, 5, 7, 2])
+
+  [2, 4, 6, 1]
+  |> list.filter_map(Error)
+  |> should.equal([])
+}
+
 pub fn map_test() {
   []
   |> list.map(fn(x) { x * 2 })