Improve R.evolve typings

types/ramda/index.d.ts

@@ -20,6 +20,7 @@
 //                 Keagan McClelland <https://github.com/CaptJakk>
 //                 Tomas Szabo <https://github.com/deftomat>
 //                 Bonggyun Lee <https://github.com/deptno>
+//                 Marcin Biernat <https://github.com/biern>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.8
 
@@ -82,9 +83,28 @@ declare namespace R {
       (obj: Dictionary<T>): Dictionary<T>;
     }
 
-    type Evolver<T> =
-        | ((x: T) => T)
-        | { [K in keyof T]?: Evolver<T[K]> };
+    type Evolve<O extends Evolvable<E>, E extends Evolver> = {
+        [P in keyof O]: P extends keyof E ? EvolveValue<O[P], E[P]> : O[P];
+    };
+
+    type EvolveValue<V, E> =
+        E extends (value: V) => any ? ReturnType<E> :
+        E extends Evolver ? EvolveNestedValue<V, E> :
+        never;
+
+    type EvolveNestedValue<V, E extends Evolver> =
+        V extends object ? (V extends Evolvable<E> ? Evolve<V, E> : never) : never;
+
+    interface Evolver {
+        [key: string]: ((value: any) => any) | Evolver;
+    }
+
+    // Represents all objects evolvable with Evolver E
+    type Evolvable<E extends Evolver> = {
+        [P in keyof E]?: E[P] extends (value: infer V) => any ? V :
+            E[P] extends Evolver ? Evolvable<E[P]> :
+            never
+    };
 
     // @see https://gist.github.com/donnut/fd56232da58d25ceecf1, comment by @albrow
     interface CurriedTypeGuard2<T1, T2, R extends T2> {
@@ -604,8 +624,8 @@ declare namespace R {
         /**
          * Creates a new object by evolving a shallow copy of object, according to the transformation functions.
          */
-        evolve<V>(transformations: Evolver<V>, obj: V): V;
-        evolve<V>(transformations: Evolver<V>): <W extends V>(obj: W) => W;
+        evolve<E extends Evolver, V extends Evolvable<E>>(transformations: E, obj: V): Evolve<V, E>;
+        evolve<E extends Evolver>(transformations: E): <V extends Evolvable<E>>(obj: V) => Evolve<V, E>;
 
         /*
          * A function that always returns false. Any passed in parameters are ignored.

types/ramda/ramda-tests.ts

@@ -1307,19 +1307,55 @@ type Pair = KeyValuePair<string, number>;
 };
 
 () => {
-    const a1 = R.evolve({elapsed: R.add(1), remaining: R.add(-1)}, {name: "Tomato", elapsed: 100, remaining: 1400});
-    const a2 = R.evolve({elapsed: R.add(1), remaining: R.add(-1)})({name: "Tomato", elapsed: 100, remaining: 1400});
-};
+    // No type transformation
 
-() => {
-    // const tomato = {firstName: 'Tomato ', data: {elapsed: 100, remaining: 1400}, id:123};
-    // const transformations = {
-    //     firstName: R.trim,
-    //     lastName: R.trim, // Will not get invoked.
-    //     data: {elapsed: R.add(1), remaining: R.add(-1)}
-    // };
-    // const a = R.evolve(transformations, tomato); // => {firstName: 'Tomato', data: {elapsed: 101, remaining: 1399}, id:123}
-    // const b = R.evolve(transformations)(tomato); // => {firstName: 'Tomato', data: {elapsed: 101, remaining: 1399}, id:123}
+    const a1 = R.evolve({ elapsed: R.add(1), remaining: R.add(-1) }, { name: "Tomato", elapsed: 100, remaining: 1400 });
+
+    const a1Test: { elapsed: number, remaining: number, name: string } = a1;
+
+    const a2 = R.evolve({ elapsed: R.add(1), remaining: R.add(-1) })({ name: "Tomato", elapsed: 100, remaining: 1400 });
+
+    const a2Test: { elapsed: number, remaining: number, name: string } = a2;
+
+    // Object doesn't have all evolver keys
+
+    const a3 = R.evolve({ age: R.add(1), name: R.trim }, { name: "Potato", elapsed: 100 });
+
+    const a3Test: { name: string, elapsed: number } = a3;
+
+    // Flat transformation
+
+    const ex0 = R.evolve({ a: parseInt }, { a: '10', b: 1 });
+
+    const ex0Test: { a: number, b: number } = ex0;
+
+    // Nested transformation:
+
+    const ex1 = R.evolve(
+        { a: { b: R.toString, d: { e: R.toString } } },
+        { a: { b: 1, c: null, d: { e: 2 } } },
+    );
+
+    const ex1Test: { a: { b: string, c: null, d: { e: string } } } = ex1;
+
+    // Mapping a nested object with a single function
+
+    const ex2 = R.evolve(
+        { a: (obj: { foo: string }) => ({ bar: 1, baz: 2 }) },
+        { a: { foo: 'a', skipped: 3 }, b: null },
+    );
+
+    const ex2Test: { a: { bar: number, baz: number }, b: null } = ex2;
+
+    // Nested curried:
+
+    const ex3 = R.evolve(
+        { a: { b: R.toString, d: { e: R.toString } } },
+    )(
+        { a: { b: 1, c: null, d: { e: 2 } } }
+    );
+
+    const ex3Test: { a: { b: string, c: null, d: { e: string } } } = ex3;
 };
 
 () => {