test.ts

type CheckValidFn = (v: any) => ValidationErrors | null;

const createValidatorFn = (...checkValids: CheckValidFn[]): ValidatorFn => {
  const check = and(...checkValids);
  const validator = (control: AbstractControl) => check(control.value);

  return validator;
};

const and = (...checkValids: CheckValidFn[]): CheckValidFn => {
  if (checkValids.length === 0) {
    return (_: any) => null;
  } else if (checkValids.length === 1) {
    return checkValids[0];
  }
  return v => {
    for (const check of checkValids) {
      const verrs = check(v);
      if (!!verrs) {
        return verrs;
      }
    }
    return null;
  };
};

const or = (...checkValids: CheckValidFn[]): CheckValidFn => {
  if (checkValids.length === 0) {
    return (_: any) => ({ or: 'no validation' });
  } else if (checkValids.length === 1) {
    return checkValids[0];
  }
  return v => {
    let errs: ValidationErrors[] = [];
    for (const check of checkValids) {
      const verr = check(v);
      if (verr == null) {
        return null;
      } else {
        errs.push(verr);
      }
    }
    return { or: errs };
  };
};

const createPredicate = (check: CheckValidFn): ((v: any) => boolean) => {
  return v => !check(v);
};