feat(partial): add partial tail function

README.md

@@ -64,6 +64,21 @@ const unary = partialRight(fn, false, 0);
 const nullary = partialRight(fn, false, 0, "");
 ```
 
+### partialTail
+
+Create tail partial applied function.
+
+Tail is any argument other than the first argument.
+
+```ts
+import { partialTail } from "https://deno.land/x/curry@$VERSION/mod.ts";
+
+declare const fn: (a: string, b: number, c: boolean) => void;
+
+const binary = partialTail(fn, 0);
+const unary = partialTail(fn, 0, false);
+```
+
 ## API
 
 See [deno doc](https://deno.land/x/curry/mod.ts) for all APIs.

mod.ts

@@ -2,4 +2,4 @@
 // This module is browser compatible.
 
 export { curry } from "./curry.ts";
-export { partial, partialRight } from "./partial.ts";
+export { partial, partialRight, partialTail } from "./partial.ts";

partial.ts

@@ -90,7 +90,37 @@ export function partialRight<AX, R>(
   ...args: AX[]
 ): (...args: readonly AX[]) => R {
   args = args.reverse();
-  return function (...rest): R {
+  return function partial(...rest): R {
     return fn.apply(null, rest.concat(args));
   };
 }
+
+/** Create tail partial applied function.
+ *
+ * Tail is any argument other than the first argument.
+ *
+ * @example
+ * ```ts
+ * import { partialTail } from "https://deno.land/x/curry@$VERSION/mod.ts";
+ *
+ * declare const fn: (a: string, b: number, c: boolean) => void;
+ *
+ * const binary = partialTail(fn, 0);
+ * const unary = partialTail(fn, 0, false);
+ * ```
+ */
+export function partialTail<
+  H,
+  T extends readonly unknown[],
+  U extends readonly unknown[],
+  R,
+>(
+  fn: (...args: readonly [H, ...T, ...U]) => R,
+  ...tail: T
+): (head: H, ...rest: U) => R {
+  function partial(head: H, ...rest: U): R {
+    return fn(head, ...tail, ...rest);
+  }
+
+  return partial;
+}

partial_test.ts

@@ -1,6 +1,6 @@
 // Copyright 2023-latest Tomoki Miyauchi. All rights reserved. MIT license.
 
-import { partial, partialRight } from "./partial.ts";
+import { partial, partialRight, partialTail } from "./partial.ts";
 import {
   assertEquals,
   assertSpyCallArgs,
@@ -238,3 +238,85 @@ describe("partialRight", () => {
     });
   });
 });
+
+describe("partialTail", () => {
+  describe("unary", () => {
+    interface Context {
+      fn: Fn2Spy<Arity1>;
+    }
+    beforeEach<Context>(function () {
+      this.fn = spy((arg1: string): string => arg1);
+    });
+
+    const arg = "";
+
+    it<Context>("should pass 0 argument", function () {
+      const fn = partialTail(this.fn);
+
+      assertEquals(fn(arg), arg);
+      assertSpyCallArgs(this.fn, 0, [arg]);
+    });
+  });
+
+  describe("binary", () => {
+    interface Context {
+      fn: Fn2Spy<Arity2>;
+    }
+    beforeEach<Context>(function () {
+      this.fn = spy((arg1: string, arg2: number): string => arg1 + arg2);
+    });
+
+    const arg = "";
+    const arg2 = 0;
+
+    it<Context>("should pass 0 argument", function () {
+      const fn = partialTail(this.fn);
+
+      assertEquals(fn(arg, arg2), arg + arg2);
+      assertSpyCallArgs(this.fn, 0, [arg, arg2]);
+    });
+
+    it<Context>("should pass 1 argument", function () {
+      const fn = partialTail(this.fn, arg2);
+
+      assertEquals(fn(arg), arg + arg2);
+      assertSpyCallArgs(this.fn, 0, [arg, arg2]);
+    });
+  });
+
+  describe("ternary", () => {
+    interface Context {
+      fn: Fn2Spy<Arity3>;
+    }
+    beforeEach<Context>(function () {
+      this.fn = spy((arg1: string, arg2: number, arg3: boolean): string =>
+        arg1 + arg2 + arg3
+      );
+    });
+
+    const arg = "";
+    const arg2 = 0;
+    const arg3 = false;
+
+    it<Context>("should pass 0 argument", function () {
+      const fn = partialTail(this.fn);
+
+      assertEquals(fn(arg, arg2, arg3), arg + arg2 + arg3);
+      assertSpyCallArgs(this.fn, 0, [arg, arg2, arg3]);
+    });
+
+    it<Context>("should pass 1 argument", function () {
+      const fn = partialTail(this.fn, arg2);
+
+      assertEquals(fn(arg, arg3), arg + arg2 + arg3);
+      assertSpyCallArgs(this.fn, 0, [arg, arg2, arg3]);
+    });
+
+    it<Context>("should pass 2 argument", function () {
+      const fn = partialTail(this.fn, arg2, arg3);
+
+      assertEquals(fn(arg), arg + arg2 + arg3);
+      assertSpyCallArgs(this.fn, 0, [arg, arg2, arg3]);
+    });
+  });
+});