things

things.js

function Tuple(a, b, c, d, e, f, g) {
  function tuplable(transformer) {
    return transformer(a, b, c, d, e, f, g);
  };

  tuplable.toString = function() {
    return 'Tuple (' + [a, b, c, d, e, f, g].filter(function(item) {
      return item != null;
    }).join(', ') + ')';
  };

  return tuplable;
}

var EmptyList = {
  toString: function() {
    return 'List []';
  }
};

function List(head, rest) {
  function listable(iterator) {
    return iterator(head, rest);
  };

  listable.toString = function() {
    return 'List [' + toJS(this).join(', ') + ']';
  };

  return listable;
}

function map(iterator, list) {
  if (list === EmptyList) {
    return list;
  } else {
    return list(function(head, rest) {
      return List(iterator(head), map(iterator, rest));
    });
  }
}

function filter(qualifier, list) {
  if (list === EmptyList) {
    return list;
  } else {
    return list(function(head, rest) {
      if (qualifier(head)) {
        return List(head, filter(qualifier, rest));
      } else {
        return filter(qualifier, rest);
      }
    });
  }
}

function reduce(accumulator, value, list) {
  if (list === EmptyList) {
    return value;
  } else {
    return list(function(head, rest) {
      return reduce(accumulator, accumulator(value, head), rest);
    });
  }
}

function concat(list, list$) {
  if (list === EmptyList) {
    return list$;
  } else {
    return list(function(head, rest) {
      return List(head, concat(rest, list$));
    });
  }
}

function concatl(list) {
  return reduce(function(result, list) {
    return concat(result, list);
  }, EmptyList, list);
}

function flatmap(iterator, list) {
  if (list === EmptyList) {
    return list;
  } else {
    return list(function(head, rest) {
      return concat(iterator(head), flatmap(iterator, rest));
    });
  }
}

function fromJS(array) {
  return array.reduceRight(function(list, element) {
    return List(element, list);
  }, EmptyList);
}

function toJS(list) {
  return reduce(function(array, element) {
    return array.concat([element]);
  }, [], list);
};

var Nothing = {
  toString: function() {
    return 'Nothing';
  }
};

function Just(value) {
  function justable(iterator) {
    return iterator(value);
  }

  justable.toString = function() {
    return 'Just ' + this;
  };

  return justable;
}