add overloads to compose.ts

src/compose.ts

@@ -1,13 +1,92 @@
+type Func0<R> = () => R
+type Func1<T1, R> = (a1: T1) => R
+type Func2<T1, T2, R> = (a1: T1, a2: T2) => R
+type Func3<T1, T2, T3, R> = (a1: T1, a2: T2, a3: T3, ...args: any[]) => R
+
 /**
  * Composes single-argument functions from right to left. The rightmost
- * function can take multiple arguments as it provides the signature for
- * the resulting composite function.
+ * function can take multiple arguments as it provides the signature for the
+ * resulting composite function.
  *
- * @param {...Function} funcs The functions to compose.
- * @returns {Function} A function obtained by composing the argument functions
- * from right to left. For example, compose(f, g, h) is identical to doing
- * (...args) => f(g(h(...args))).
+ * @param funcs The functions to compose.
+ * @returns R function obtained by composing the argument functions from right
+ *   to left. For example, `compose(f, g, h)` is identical to doing
+ *   `(...args) => f(g(h(...args)))`.
  */
+export default function compose(): <R>(a: R) => R
+
+export default function compose<F extends Function>(f: F): F
+
+/* two functions */
+export default function compose<A, R>(f1: (b: A) => R, f2: Func0<A>): Func0<R>
+export default function compose<A, T1, R>(
+  f1: (b: A) => R,
+  f2: Func1<T1, A>
+): Func1<T1, R>
+export default function compose<A, T1, T2, R>(
+  f1: (b: A) => R,
+  f2: Func2<T1, T2, A>
+): Func2<T1, T2, R>
+export default function compose<A, T1, T2, T3, R>(
+  f1: (b: A) => R,
+  f2: Func3<T1, T2, T3, A>
+): Func3<T1, T2, T3, R>
+
+/* three functions */
+export default function compose<A, B, R>(
+  f1: (b: B) => R,
+  f2: (a: A) => B,
+  f3: Func0<A>
+): Func0<R>
+export default function compose<A, B, T1, R>(
+  f1: (b: B) => R,
+  f2: (a: A) => B,
+  f3: Func1<T1, A>
+): Func1<T1, R>
+export default function compose<A, B, T1, T2, R>(
+  f1: (b: B) => R,
+  f2: (a: A) => B,
+  f3: Func2<T1, T2, A>
+): Func2<T1, T2, R>
+export default function compose<A, B, T1, T2, T3, R>(
+  f1: (b: B) => R,
+  f2: (a: A) => B,
+  f3: Func3<T1, T2, T3, A>
+): Func3<T1, T2, T3, R>
+
+/* four functions */
+export default function compose<A, B, C, R>(
+  f1: (b: C) => R,
+  f2: (a: B) => C,
+  f3: (a: A) => B,
+  f4: Func0<A>
+): Func0<R>
+export default function compose<A, B, C, T1, R>(
+  f1: (b: C) => R,
+  f2: (a: B) => C,
+  f3: (a: A) => B,
+  f4: Func1<T1, A>
+): Func1<T1, R>
+export default function compose<A, B, C, T1, T2, R>(
+  f1: (b: C) => R,
+  f2: (a: B) => C,
+  f3: (a: A) => B,
+  f4: Func2<T1, T2, A>
+): Func2<T1, T2, R>
+export default function compose<A, B, C, T1, T2, T3, R>(
+  f1: (b: C) => R,
+  f2: (a: B) => C,
+  f3: (a: A) => B,
+  f4: Func3<T1, T2, T3, A>
+): Func3<T1, T2, T3, R>
+
+/* rest */
+export default function compose<R>(
+  f1: (b: any) => R,
+  ...funcs: Function[]
+): (...args: any[]) => R
+
+export default function compose<R>(...funcs: Function[]): (...args: any[]) => R
 
 export default function compose(...funcs: Function[]) {
   if (funcs.length === 0) {