Make minor improvements to function.js

[Pisces] / function.js

// SPDX-FileCopyrightText: 2022, 2023, 2025 Lady <https://www.ladys.computer/about/#lady>
// SPDX-License-Identifier: MPL-2.0
/**
 * ⁌ ♓🧩 Piscēs ∷ function.js
 *
 * Copyright © 2022–2023, 2025 Lady [@ Ladys Computer].
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at <https://mozilla.org/MPL/2.0/>.
 */

import {
  ITERATOR,
  toFunctionName,
  toLength,
  type,
  UNDEFINED,
} from "./value.js";
import {
  defineOwnDataProperty,
  defineOwnProperties,
  defineOwnProperty,
  getOwnPropertyDescriptor,
  getPrototype,
  hasOwnProperty,
  objectCreate,
  setPropertyValues,
  setPrototype,
} from "./object.js";

const PISCĒS = "♓🧩 Piscēs";

export const {
  /**
   * Creates a bound function from the provided function using the
   * provided this value and arguments list.
   *
   * ☡ As with `call´ and `construct´, the arguments must be passed as
   * an array.
   */
  bind,

  /**
   * Returns a new arrow function function which wraps the provided
   * function and passes its arguments thru.
   *
   * The `length´, `name´, and prototype of the provided function will
   * be preserved in the new one. A second argument may be used to
   * override `length´ and `name´.
   */
  createArrowFunction,

  /**
   * Returns a new arrow function which wraps the provided function,
   * using its first argument as the this value when calling the
   * provided function and passing the remainder thru.
   *
   * The `length´, `name´, and prototype of the provided function will
   * be preserved in the new one. A second argument may be used to
   * override `length´ and `name´.
   *
   * ※ This is effectively an alias for `Function::call.bind´.
   */
  createCallableFunction,

  /**
   * Returns a constructor which throws whenever it is called but has
   * the same `.length´, `.name´, and `.prototype´ as the provided
   * value.
   *
   * The `length´, `name´, `prototype´, and prototype of the provided
   * function will be preserved in the new one. A second argument may
   * be used to override `length´, `name´, and `prototype´.
   */
  createIllegalConstructor,

  /**
   * Returns a constructor which produces a new constructor that wraps
   * the provided constructor, but returns a proxy of the result using
   * the provided handler.
   *
   * The resulting constructor inherits from, and has the same basic
   * shape as, `Proxy´.
   *
   * If a base constructor is not provided, `Object´ will be used.
   *
   * If a third argument is provided, it is used as the target for the
   * provided constructor when it is constructed. This can be used to
   * prevent leakage of the provided constructor to superclasses
   * through `new.target´.
   *
   * The `length´ of the provided function will be preserved in the new
   * one. A fourth argument may be used to override `length´ and
   * `name´.
   *
   * ※ `.prototype´ will be present, but undefined, on the resulting
   * constructor. This differs from the behaviour of `Proxy´, for which
   * `.prototype´ is not present at all. It is not presently possible
   * to create a constructor with no `.prototype´ property in
   * Ecmascript code.
   */
  createProxyConstructor,
} = (() => {
  const { prototype: functionPrototype } = Function;
  const {
    bind: functionBind,
    call: functionCall,
  } = functionPrototype;
  const objectConstructor = Object;
  const proxyConstructor = Proxy;
  const {
    apply: reflectApply,
    construct: reflectConstruct,
  } = Reflect;
  const callBind = reflectApply(functionBind, functionCall, [
    functionBind,
  ]);
  const { revocable } = Proxy;
  const { [ITERATOR]: arrayIterator } = Array.prototype;
  const {
    next: arrayIteratorNext,
  } = getPrototype([][ITERATOR]());
  const argumentIterablePrototype = {
    [ITERATOR]() {
      return {
        [ITERATOR]() {
          return this;
        },
        next: callBind(
          arrayIteratorNext,
          reflectApply(arrayIterator, this.args, []),
        ),
      };
    },
  };
  const { get: wmGet, set: wmSet } = WeakMap.prototype;
  const wsConstructor = WeakSet;
  const { add: wsAdd, has: wsHas } = WeakSet.prototype;
  const proxyConstructorValuesMap = new WeakMap();
  const registerConstructedProxy = (constructor, proxy) => {
    const values = (() => {
      const existing = reflectApply(wmGet, proxyConstructorValuesMap, [
        constructor,
      ]);
      if (existing) {
        // There is an existing values set for this constructor.
        //
        // It is returned.
        return existing;
      } else {
        // There is no existing values set for this constructor so one
        // must be created.
        const result = new wsConstructor();
        reflectApply(wmSet, proxyConstructorValuesMap, [
          constructor,
          result,
        ]);
        return result;
      }
    })();
    reflectApply(wsAdd, values, [proxy]);
    return proxy;
  };
  const applyBaseFunction = ($, base, lengthDelta = 0) => {
    if (base === UNDEFINED) {
      // No base function was provided to apply.
      return $;
    } else {
      // A base function was provided.
      //
      // Apply it.
      const overrides = objectCreate(null);
      overrides.length = +base.length + lengthDelta;
      overrides.name = base.name;
      if (getPrototype($) === functionPrototype) {
        // The provided function has the function prototype.
        //
        // Change it to match the base function.
        setPrototype($, getPrototype(base));
      } else {
        // The provided function already does not have the function
        // prototype, so its prototype is not changed.
        /* do nothing */
      }
      if (hasOwnProperty($, "prototype") && "prototype" in base) {
        // The provided function has a `.prototype´ property, and one
        // was provided in the base function as well.
        try {
          // If this does not throw, the provided function is a
          // constructor. Its `.prototype´ property is set alongside
          // the others.
          reflectConstruct(function () {}, [], $);
          overrides.prototype = base.prototype;
        } catch {
          // The provided function is not a constructor.
          /* do nothing */
        }
      } else {
        // The provided function does not have a `.prototype´ property,
        // or the base function did not have one.
        /* do nothing */
      }
      return applyProperties($, overrides);
    }
  };
  const applyProperties = ($, override) => {
    if (override === UNDEFINED) {
      // No properties were provided to apply.
      return $;
    } else {
      // Properties were provided.
      //
      // Apply them.
      const { length, name } = override;
      if (
        !("prototype" in override)
        || !getOwnPropertyDescriptor($, "prototype")?.writable
      ) {
        // The provided function has no `.prototype´, its prototype is
        // not writable, or no prototype value was provided.
        //
        // Do not modify the prototype property of the provided
        // function.
        /* do nothing */
      } else {
        // The provided function has a writable `.prototype´ and a
        // prototype value was provided.
        //
        // Change the prototype property of the provided function to
        // match.
        defineOwnProperty(
          $,
          "prototype",
          defineOwnDataProperty(
            objectCreate(null),
            "value",
            override.prototype,
          ),
        );
      }
      return defineOwnProperties($, {
        length: defineOwnDataProperty(
          objectCreate(null),
          "value",
          toLength(length === UNDEFINED ? $.length : length),
        ),
        name: defineOwnDataProperty(
          objectCreate(null),
          "value",
          toFunctionName(name === UNDEFINED ? $.name ?? "" : name),
        ),
      });
    }
  };

  return {
    bind: ($, boundThis, boundArgs) =>
      callBind(
        $,
        boundThis,
        ...defineOwnDataProperty(
          objectCreate(argumentIterablePrototype),
          "args",
          boundArgs,
        ),
      ),
    createArrowFunction: ($, propertyOverride = UNDEFINED) =>
      applyProperties(
        applyBaseFunction(
          (...$s) => reflectApply($, UNDEFINED, $s),
          $,
        ),
        propertyOverride,
      ),
    createCallableFunction: ($, propertyOverride = UNDEFINED) =>
      applyProperties(
        applyBaseFunction(
          (...$s) => {
            const iterator = defineOwnDataProperty(
              objectCreate(argumentIterablePrototype),
              "args",
              $s,
            )[ITERATOR]();
            const { value: thisValue } = iterator.next();
            return reflectApply($, thisValue, [...iterator]);
          },
          $,
          1,
        ),
        propertyOverride,
      ),
    createIllegalConstructor: ($, propertyOverride = UNDEFINED) =>
      defineOwnProperty(
        applyProperties(
          applyBaseFunction(
            function () {
              throw new TypeError("Illegal constructor");
            },
            $,
          ),
          propertyOverride,
        ),
        "prototype",
        { writable: false },
      ),
    createProxyConstructor: (
      handler,
      $,
      newTarget = UNDEFINED,
      propertyOverride = UNDEFINED,
    ) => {
      const constructor = $ === UNDEFINED
        ? function ($) {
          return new objectConstructor($);
        }
        : $;
      const target = newTarget === UNDEFINED ? constructor : newTarget;
      const len = toLength(constructor.length);
      if (!(type(handler) === "object")) {
        // The provided handler is not an object; this is an error.
        throw new TypeError(
          `${PISCĒS}: Proxy handler must be an object, but got: ${handler}.`,
        );
      } else if (!isConstructor(constructor)) {
        // The provided constructor is not a constructor; this is an
        // error.
        throw new TypeError(
          `${PISCĒS}: Cannot create proxy constructor from nonconstructible value.`,
        );
      } else if (!isConstructor(target)) {
        // The provided new target is not a constructor; this is an
        // error.
        throw new TypeError(
          `${PISCĒS}: New target must be a constructor.`,
        );
      } else {
        // The arguments are acceptable.
        const C = applyProperties(
          defineOwnProperties(
            setPrototype(
              function (...$s) {
                if (new.target === UNDEFINED) {
                  // The constructor was not called with new; this is
                  // an error.
                  throw new TypeError(
                    `${PISCĒS}: ${
                      C.name ?? "Proxy"
                    } must be called with new.`,
                  );
                } else {
                  // The constructor was called with new.
                  //
                  // Return the appropriate proxy.
                  const O = reflectConstruct(
                    constructor,
                    $s,
                    target,
                  );
                  const proxy = new proxyConstructor(O, handler);
                  return registerConstructedProxy(C, proxy);
                }
              },
              proxyConstructor,
            ),
            {
              length: defineOwnDataProperty(
                objectCreate(null),
                "value",
                len,
              ),
              name: defineOwnDataProperty(
                objectCreate(null),
                "value",
                `${toFunctionName(constructor.name ?? "")}Proxy`,
              ),
              prototype: setPropertyValues(objectCreate(null), {
                configurable: false,
                enumerable: false,
                value: UNDEFINED,
                writable: false,
              }),
            },
          ),
          propertyOverride,
        );
        const { name } = C;
        return defineOwnProperties(C, {
          revocable: setPropertyValues(objectCreate(null), {
            configurable: true,
            enumerable: false,
            value: defineOwnProperties(
              (...$s) => {
                const O = reflectConstruct(
                  constructor,
                  $s,
                  target,
                );
                const proxy = revocable(O, handler);
                return registerConstructedProxy(C, proxy);
              },
              {
                length: defineOwnDataProperty(
                  objectCreate(null),
                  "value",
                  len,
                ),
                name: defineOwnDataProperty(
                  objectCreate(null),
                  "value",
                  "revocable",
                ),
              },
            ),
            writable: true,
          }),
          [`is${name}`]: setPropertyValues(objectCreate(null), {
            configurable: true,
            enumerable: false,
            value: defineOwnProperty(
              ($) => {
                const values = reflectApply(
                  wmGet,
                  proxyConstructorValuesMap,
                  [C],
                );
                if (values === UNDEFINED) {
                  // No values have been registered for the current
                  // constructor.
                  return false;
                } else {
                  // One or more values has been registered for the
                  // current constructor.
                  //
                  // Return whether the provided argument is one.
                  return reflectApply(wsHas, values, [$]);
                }
              },
              "name",
              defineOwnDataProperty(
                objectCreate(null),
                "value",
                `is${name}`,
              ),
            ),
            writable: true,
          }),
        });
      }
    },
  };
})();

/**
 * Calls the provided function with the provided this value and
 * arguments list.
 *
 * ☡ This is effectively an alias for `Reflect.apply´—the arguments
 * must be passed as an arraylike.
 */
export const call = createArrowFunction(Reflect.apply, {
  name: "call",
});

/**
 * Returns whether calling the provided function with no this value
 * or arguments completes normally; that is, does not throw an error.
 *
 * ☡ This function will throw an error if the provided argument is not
 * callable.
 */
export const completesNormally = ($) => {
  if (!isCallable($)) {
    // The provided value is not callable; this is an error.
    throw new TypeError(
      `${PISCĒS}: Cannot determine completion of noncallable value: ${$}.`,
    );
  } else {
    // The provided value is callable.
    try {
      // This will throw if calling the function throws.
      //
      // Otherwise, return true.
      $();
      return true;
    } catch {
      // Calling the function did not succeed.
      //
      // Return false.
      return false;
    }
  }
};

/**
 * Constructs the provided function with the provided arguments list
 * and new target.
 *
 * ☡ This is effectively an alias for `Reflect.construct´—the
 * arguments must be passed as an arraylike.
 */
export const construct = createArrowFunction(Reflect.construct);

/**
 * Returns the provided value.
 *
 * ※ This function can be called as a constructor. When used in an
 * `extends´ clause and called via `super´, it will set the value of
 * `this´ to the provided value, enabling it to be extended with
 * private class features.
 */
export const identity = function ($) {
  return $;
};

/** Returns whether the provided value is callable. */
export const isCallable = ($) => typeof $ === "function";

/** Returns whether the provided value is a constructor. */
export const isConstructor = ($) =>
  completesNormally(() =>
    // Try constructing a new object using the provided value as
    // `new.target´.
    //
    // ☡ This will throw if the provided value is not a constructor.
    construct(function () {}, [], $)
  );

/**
 * Calls the provided callback with the provided argument if the
 * provided argument is not nullish; otherwise, returns the provided
 * argument unmodified.
 */
export const maybe = ($, callback) => $ == null ? $ : callback($);

/**
 * Returns whether the provided object inherits from the prototype of
 * the provided function.
 */
export const ordinaryHasInstance = createCallableFunction(
  Function.prototype[Symbol.hasInstance],
  { name: "ordinaryHasInstance" },
);