Curry map

Author: lpil

CHANGELOG.md

@@ -3,6 +3,8 @@
 ## v0.19.1 - 2022-01-09
 
 - The `dynamic.dynamic` function now returns a result.
+- The `dynamic.map` function is now curried and requires the decoders for keys
+  and values to be supplied.
 - The `dynamic.result`, `dynamic.optional`, `dynamic.field`, and `dynamic.list`
   functions are now partially applied.
 

src/gleam/dynamic.gleam

@@ -841,8 +841,27 @@ pub fn tuple6(
 /// Error(DecodeError(expected: "Map", found: "String", path: []))
 /// ```
 ///
-pub fn map(from value: Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeErrors) {
-  decode_map(value)
+pub fn map(
+  of key_type: Decoder(k),
+  to value_type: Decoder(v),
+) -> Decoder(Map(k, v)) {
+  fn(value) {
+    try map = decode_map(value)
+    try pairs =
+      map
+      |> map.to_list
+      |> list.try_map(fn(pair) {
+        let #(k, v) = pair
+        try k =
+          key_type(k)
+          |> map_errors(push_path(_, "keys"))
+        try v =
+          value_type(v)
+          |> map_errors(push_path(_, "values"))
+        Ok(#(k, v))
+      })
+    Ok(map.from_list(pairs))
+  }
 }
 
 if erlang {

test/gleam/dynamic_test.gleam

@@ -699,12 +699,31 @@ pub fn nested_tuples_test() {
 pub fn map_test() {
   map.new()
   |> dynamic.from
-  |> dynamic.map
+  |> dynamic.map(dynamic.string, dynamic.int)
   |> should.equal(Ok(map.new()))
 
+  map.from_list([#("a", 1), #("b", 2)])
+  |> dynamic.from
+  |> dynamic.map(dynamic.string, dynamic.int)
+  |> should.equal(Ok(map.from_list([#("a", 1), #("b", 2)])))
+
+  map.from_list([#("a", 1), #("b", 2)])
+  |> dynamic.from
+  |> dynamic.map(dynamic.int, dynamic.int)
+  |> should.equal(Error([
+    DecodeError(expected: "Int", found: "String", path: ["keys"]),
+  ]))
+
+  map.from_list([#("a", 1), #("b", 2)])
+  |> dynamic.from
+  |> dynamic.map(dynamic.string, dynamic.string)
+  |> should.equal(Error([
+    DecodeError(expected: "String", found: "Int", path: ["values"]),
+  ]))
+
   1
   |> dynamic.from
-  |> dynamic.map
+  |> dynamic.map(dynamic.string, dynamic.int)
   |> should.equal(Error([DecodeError(expected: "Map", found: "Int", path: [])]))
 }