Lady’s Gitweb - Pisces/blob - function.js

   1 // ♓🌟 Piscēs ∷ function.js
   2 // ====================================================================
   3 //
   4 // Copyright © 2022‐2023 Lady [@ Lady’s Computer].
   5 //
   6 // This Source Code Form is subject to the terms of the Mozilla Public
   7 // License, v. 2.0. If a copy of the MPL was not distributed with this
   8 // file, You can obtain one at <https://mozilla.org/MPL/2.0/>.
   9
  10 import {
  11   ITERATOR,
  12   toFunctionName,
  13   toLength,
  14   type,
  15   UNDEFINED,
  16 } from "./value.js";
  17 import {
  18   defineOwnDataProperty,
  19   defineOwnProperties,
  20   defineOwnProperty,
  21   getOwnPropertyDescriptor,
  22   getPrototype,
  23   objectCreate,
  24   setPropertyValues,
  25   setPrototype,
  26 } from "./object.js";
  27
  28 export const {
  29   /**
  30    * Creates a bound function from the provided function using the
  31    * provided this value and arguments list.
  32    *
  33    * ☡ As with `call` and `construct`, the arguments must be passed as
  34    * an array.
  35    */
  36   bind,
  37
  38   /**
  39    * Returns a new function which calls the provided function with its
  40    * first argument as the `this` value and the remaining arguments
  41    * passed through.
  42    *
  43    * The `length`, `name`, and prototype of the provided function will
  44    * be preserved in the new one. A second argument may be used to
  45    * override `length` and `name`.
  46    */
  47   createArrowFunction,
  48
  49   /**
  50    * Returns a new function which calls the provided function with its
  51    * first argument as the `this` value and the remaining arguments
  52    * passed through.
  53    *
  54    * The `length`, `name`, and prototype of the provided function will
  55    * be preserved in the new one. A second argument may be used to
  56    * override `length` and `name`.
  57    *
  58    * ※ This is effectively an alias for `Function::call.bind`.
  59    */
  60   createCallableFunction,
  61
  62   /**
  63    * Returns a constructor which throws whenever it is called but has
  64    * the same `.name` and `.prototype` as the provided value.
  65    *
  66    * The `length`, `name`, `prototype`, and prototype of the provided
  67    * function will be preserved in the new one. A second argument may
  68    * be used to override `length`, `name`, and `prototype`.
  69    */
  70   createIllegalConstructor,
  71
  72   /**
  73    * Returns a constructor which produces a new constructor which wraps
  74    * the provided constructor, but returns a proxy of the result using
  75    * the provided handler.
  76    *
  77    * The resulting constructor inherits from, and has the same basic
  78    * shape as, `Proxy`.
  79    *
  80    * If a base constructor is not provided, `Object` will be used.
  81    *
  82    * If a third argument is provided, it is used as the target for the
  83    * provided constructor when it is constructed. This can be used to
  84    * prevent leakage of the provided constructor to superclasses
  85    * through `new.target`.
  86    *
  87    * The `length` of the provided function will be preserved in the new
  88    * one. A fourth argument may be used to override `length` and
  89    * `name`.
  90    *
  91    * ※ `.prototype` will be present, but undefined, on the resulting
  92    * constructor. This differs from the behaviour of `Proxy`, for which
  93    * `.prototype` is not present at all. It is not presently possible
  94    * to create a constructor with no `.prototype` property in
  95    * Ecmascript code.
  96    */
  97   createProxyConstructor,
  98 } = (() => {
  99   const { prototype: functionPrototype } = Function;
 100   const {
 101     bind: functionBind,
 102     call: functionCall,
 103   } = functionPrototype;
 104   const objectConstructor = Object;
 105   const proxyConstructor = Proxy;
 106   const {
 107     apply: reflectApply,
 108     construct: reflectConstruct,
 109   } = Reflect;
 110   const callBind = reflectApply(functionBind, functionCall, [
 111     functionBind,
 112   ]);
 113   const { revocable } = Proxy;
 114   const { [ITERATOR]: arrayIterator } = Array.prototype;
 115   const {
 116     next: arrayIteratorNext,
 117   } = getPrototype([][ITERATOR]());
 118   const argumentIterablePrototype = {
 119     [ITERATOR]() {
 120       return {
 121         [ITERATOR]() {
 122           return this;
 123         },
 124         next: callBind(
 125           arrayIteratorNext,
 126           call(arrayIterator, this.args, []),
 127         ),
 128       };
 129     },
 130   };
 131   const applyBaseFunction = ($, base, lengthDelta = 0) => {
 132     if (base === UNDEFINED) {
 133       // No base function was provided to apply.
 134       return $;
 135     } else {
 136       // A base function was provided; apply it.
 137       const { length, name, prototype } = base;
 138       if (getPrototype($) === functionPrototype) {
 139         setPrototype($, getPrototype(base));
 140       } else {
 141         /* do nothing */
 142       }
 143       return applyProperties($, {
 144         length: +length + lengthDelta,
 145         name,
 146         prototype,
 147       });
 148     }
 149   };
 150   const applyProperties = ($, override) => {
 151     if (override === UNDEFINED) {
 152       // No properties were provided to apply.
 153       return $;
 154     } else {
 155       // Properties were provided; apply them.
 156       const { length, name, prototype } = override;
 157       if (
 158         prototype === UNDEFINED ||
 159         !getOwnPropertyDescriptor($, "prototype")?.writable
 160       ) {
 161         // The provided function has no `.prototype`, its prototype is
 162         // not writable, or no prototype value was provided.
 163         //
 164         // Do not modify the prototype property of the provided
 165         // function.
 166         /* do nothing */
 167       } else {
 168         // The provided function is a constructor and a prototype value
 169         // was provided.
 170         //
 171         // Change the prototype property of the provided function to
 172         // match.
 173         defineOwnProperty(
 174           $,
 175           "prototype",
 176           defineOwnDataProperty(
 177             objectCreate(null),
 178             "value",
 179             prototype,
 180           ),
 181         );
 182       }
 183       return defineOwnProperties($, {
 184         length: defineOwnDataProperty(
 185           objectCreate(null),
 186           "value",
 187           toLength(length === UNDEFINED ? $.length : length),
 188         ),
 189         name: defineOwnDataProperty(
 190           objectCreate(null),
 191           "value",
 192           toFunctionName(name === UNDEFINED ? $.name ?? "" : name),
 193         ),
 194       });
 195     }
 196   };
 197
 198   return {
 199     bind: ($, boundThis, boundArgs) =>
 200       callBind(
 201         $,
 202         boundThis,
 203         ...defineOwnDataProperty(
 204           objectCreate(argumentIterablePrototype),
 205           "args",
 206           boundArgs,
 207         ),
 208       ),
 209     createArrowFunction: ($, propertyOverride = UNDEFINED) =>
 210       applyProperties(
 211         applyBaseFunction(
 212           (...$s) => reflectApply($, UNDEFINED, $s),
 213           $,
 214         ),
 215         propertyOverride,
 216       ),
 217     createCallableFunction: ($, propertyOverride = UNDEFINED) =>
 218       applyProperties(
 219         applyBaseFunction(
 220           (...$s) => {
 221             const iterator = defineOwnDataProperty(
 222               objectCreate(argumentIterablePrototype),
 223               "args",
 224               $s,
 225             )[ITERATOR]();
 226             const { value: thisValue } = iterator.next();
 227             return reflectApply($, thisValue, [...iterator]);
 228           },
 229           $,
 230           1,
 231         ),
 232         propertyOverride,
 233       ),
 234     createIllegalConstructor: ($, propertyOverride = UNDEFINED) =>
 235       defineOwnProperty(
 236         applyProperties(
 237           applyBaseFunction(
 238             function () {
 239               throw new TypeError("Illegal constructor");
 240             },
 241             $,
 242           ),
 243           propertyOverride,
 244         ),
 245         "prototype",
 246         { writable: false },
 247       ),
 248     createProxyConstructor: (
 249       handler,
 250       $,
 251       newTarget = UNDEFINED,
 252       propertyOverride = UNDEFINED,
 253     ) => {
 254       const constructor = $ === UNDEFINED ? objectConstructor : $;
 255       const target = newTarget === UNDEFINED ? constructor : newTarget;
 256       const len = toLength(constructor.length);
 257       if (!(type(handler) === "object")) {
 258         // The provided handler is not an object; this is an error.
 259         throw new TypeError(
 260           `Piscēs: Proxy handler must be an object, but got: ${handler}.`,
 261         );
 262       } else if (!isConstructor(constructor)) {
 263         // The provided constructor is not a constructor; this is an
 264         // error.
 265         throw new TypeError(
 266           "Piscēs: Cannot create proxy constructor from nonconstructible value.",
 267         );
 268       } else if (!isConstructor(target)) {
 269         // The provided new target is not a constructor; this is an
 270         // error.
 271         throw new TypeError(
 272           "Piscēs: New target must be a constructor.",
 273         );
 274       } else {
 275         // The arguments are acceptable.
 276         return applyProperties(
 277           defineOwnProperties(
 278             setPrototype(
 279               function C(...$s) {
 280                 if (new.target === UNDEFINED) {
 281                   // The constructor was not called with new; this is
 282                   // an error.
 283                   throw new TypeError(
 284                     `Piscēs: ${
 285                       C.name ?? "Proxy"
 286                     } must be called with new.`,
 287                   );
 288                 } else {
 289                   // The constructor was called with new; return the
 290                   // appropriate proxy.
 291                   const O = reflectConstruct(
 292                     constructor,
 293                     $s,
 294                     target,
 295                   );
 296                   return new proxyConstructor(O, handler);
 297                 }
 298               },
 299               proxyConstructor,
 300             ),
 301             {
 302               length: defineOwnDataProperty(
 303                 objectCreate(null),
 304                 "value",
 305                 len,
 306               ),
 307               name: defineOwnDataProperty(
 308                 objectCreate(null),
 309                 "value",
 310                 `${toFunctionName(constructor.name ?? "")}Proxy`,
 311               ),
 312               prototype: setPropertyValues(objectCreate(null), {
 313                 configurable: false,
 314                 enumerable: false,
 315                 value: UNDEFINED,
 316                 writable: false,
 317               }),
 318               revocable: setPropertyValues(objectCreate(null), {
 319                 configurable: true,
 320                 enumerable: false,
 321                 value: defineOwnProperties(
 322                   (...$s) => {
 323                     const O = reflectConstruct(
 324                       constructor,
 325                       $s,
 326                       target,
 327                     );
 328                     return revocable(O, handler);
 329                   },
 330                   {
 331                     length: defineOwnDataProperty(
 332                       objectCreate(null),
 333                       "value",
 334                       len,
 335                     ),
 336                     name: defineOwnDataProperty(
 337                       objectCreate(null),
 338                       "value",
 339                       "revocable",
 340                     ),
 341                   },
 342                 ),
 343                 writable: true,
 344               }),
 345             },
 346           ),
 347           propertyOverride,
 348         );
 349       }
 350     },
 351   };
 352 })();
 353
 354 /**
 355  * Calls the provided function with the provided this value and
 356  * arguments list.
 357  *
 358  * ☡ This is effectively an alias for `Reflect.apply`—the arguments
 359  * must be passed as an arraylike.
 360  */
 361 export const call = createArrowFunction(Reflect.apply, {
 362   name: "call",
 363 });
 364
 365 /**
 366  * Returns whether calling the provided function with no `this` value
 367  * or arguments completes normally; that is, does not throw an error.
 368  *
 369  * ☡ This function will throw an error if the provided argument is not
 370  * callable.
 371  */
 372 export const completesNormally = ($) => {
 373   if (!isCallable($)) {
 374     // The provided value is not callable; this is an error.
 375     throw new TypeError(
 376       `Piscēs: Cannot determine completion of noncallable value: ${$}`,
 377     );
 378   } else {
 379     // The provided value is callable.
 380     try {
 381       // Attempt to call the function and return true if this succeeds.
 382       $();
 383       return true;
 384     } catch {
 385       // Calling the function did not succeed; return false.
 386       return false;
 387     }
 388   }
 389 };
 390
 391 /**
 392  * Constructs the provided function with the provided arguments list
 393  * and new target.
 394  *
 395  * ☡ This is effectively an alias for `Reflect.construct`—the
 396  * arguments must be passed as an arraylike.
 397  */
 398 export const construct = createArrowFunction(Reflect.construct);
 399
 400 /**
 401  * Returns the provided value.
 402  *
 403  * ※ This function can be called as a constructor. When used in an
 404  * `extends` clause and called via `super`, it will set the value of
 405  * `this` to the provided value, enabling it to be extended with
 406  * private class features.
 407  */
 408 export const identity = function ($) {
 409   return $;
 410 };
 411
 412 /** Returns whether the provided value is callable. */
 413 export const isCallable = ($) => typeof $ === "function";
 414
 415 /** Returns whether the provided value is a constructor. */
 416 export const isConstructor = ($) =>
 417   completesNormally(() =>
 418     // Try constructing a new object with the provided value as its
 419     // `new.target`. This will throw if the provided value is not a
 420     // constructor.
 421     construct(function () {}, [], $)
 422   );
 423
 424 /**
 425  * Returns whether the provided object inherits from the prototype of
 426  * the provided function.
 427  */
 428 export const ordinaryHasInstance = createCallableFunction(
 429   Function.prototype[Symbol.hasInstance],
 430   { name: "ordinaryHasInstance" },
 431 );