Review: Monorail for iPhone and iPad

Glenn Iba recently wrote me about his puzzle game Monorail for iPhone and iPad.
There was no need to: that game was already installed on my iPod and it's one of the most interesting puzzles I know.

The goal of the game is deceptively simple. You start with a grid of points, with some pre-drawn lines connecting a few dots:

Starting from there, you have to draw a closed loop that touches all points and doesn't intersect itself, like this:

All the grids provided have a unique solution, which is somewhat surprising initially: the pre-drawn lines are such subtle clues that they almost don't seem to be there.

These puzzles are also known as "Round Trip", and have been published in magazines since the early 1990's. Glenn Iba has collected some of them in a book; an extended introduction is available on his web site. It is an interesting read and shows how to approach the puzzles with logical reasoning without trial and error.

The puzzles are similar to Slitherlink, the differences being that in Slitherlink the path doesn't have to touch every point, and the clues are numbers instead of lines. Due to the lack of numbers, I consider Round Trip a "purer", more elegant puzzle.

In addition to the traditional square grid arrangement, Monorail also contains puzzles laid out on a hexagonal grid, like this:

The game contains 50 free grids. If you want to play more, there are a few packs available through in-app purchases, for a total of over 800 grids.


The user interface is quick and easy to use, and it makes the game enjoyable. The only criticism I have is the same one that I made for CounterBalancE: there is no way to put a cross on the grid, as a reminder that a line cannot be in that position. This is odd since the use of crosses is explained in the book introduction I mentioned above, so the author clearly knows that they are useful. Annoyingly, the feature was actually available in an earlier version of the game, but was removed when the undo/redo functionality was added. It would be great if it could be reintroduced in a future update.

Summary

Nontrivialness	★★★★☆
Logical Reasoning	★★★★☆
User Interface	★★★☆☆
Presentation	★★★☆☆
Loading Time	★★★★★
Saves Partial Progress	✘
Status Bar	✘

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