createDerivation

Source Code

(valuesEqual) => {
  /*~
   * type: ('a, 'a) => Boolean
   */
  const equals = (a, b) => {
    // identical objects must be equal
    if (a === b)  return true;

    // we require both values to be setoids if one of them is
    const leftSetoid  = isSetoid(a);
    const rightSetoid = isSetoid(b);
    if (leftSetoid) {
      if (rightSetoid)  return flEquals(a, b);
      else              return false;
    }

    // fall back to the provided equality
    return valuesEqual(a, b);
  };


  /*~
   * type: (Object Any, Object Any, Array String) => Boolean
   */
  const compositesEqual = (a, b, keys) => {
    for (let i = 0; i < keys.length; ++i) {
      const keyA = a[keys[i]];
      const keyB = b[keys[i]];
      if (!(equals(keyA, keyB))) {
        return false;
      }
    }
    return true;
  };


  const derivation = (variant, adt) => {
    /*~
     * stability: experimental
     * module: null
     * authors:
     *   - "@boris-marinov"
     *   - Quildreen Motta
     * 
     * type: |
     *   forall S, a:
     *     (S a).(S a) => Boolean
     *   where S is Setoid
     */
    variant.prototype.equals = function(value) {
      assertType(adt)(`${this[tagSymbol]}#equals`, value);
      return sameType(this, value) && compositesEqual(this, value, Object.keys(this));
    };
    provideAliases(variant.prototype);
    return variant;
  };
  copyDocs(createDerivation, derivation, {
    type: '(Variant, Union) => Void'
  });


  return derivation;
}