Paper:
ABSTRACT AI today is far from being able to write complex programs. What type of problems would best teach computers programming, and how should such problems be generated? We suggest programming puzzles as a domain for teaching computers programming. A programming puzzle is a short program for a Boolean function f (x) with the goal of finding an input that makes f return True. Puzzles are objective in that one can easily test the correctness of a candidate solution, in contrast to other common specifications for program synthesis like input-output pairs or English problem descriptions. To address automatic puzzle generation, we propose a GAN-like algorithm called "Troublemaker" which can generate puzzles adaptively targeted at any given puzzle-solver. Rather than generating a single dataset of puzzles at random, it generates a diverse set of puzzles that are difficult for the solver. In our experiments, Troublemaker learns to generate challenging problems for a variety of state-of-the-art puzzle-solving techniques.

Review:
This paper proposes a trainable 'puzzle' program synthesizer that outputs a program f with a specific syntax. These 'puzzles' are structured as boolean programs, and a program solver solves the puzzle by finding an input x such that f(x) = True.  The authors motivate this task by making a case that puzzles of this sort are a good domain for teaching computers how to program.
The paper is fairly clear overall. There is some repetition in the early parts, so this could be restructured a bit, but these are minor points. A more significant restructuring however, is that this work would benefit from the related work being present the beginning of the work. Since this work is so similar in many ways to previous work I think the overall clarity of the paper would be improved, and the contributions clearer, if the work was better situated with respect to related work.
The experiments demonstrate that the trainable puzzle generator is able to produce harder (i.e. takes longer time to solve) puzzles than a random or probabilistic generator of the same grammar. While this does show that the program generator is learning something useful, these results are insufficient to show the utility of this approach in any real context. It seems the most interesting solver to assess is a trainable solver. Yet only 1 of the 4  solvers they assess is trainable. I know the authors make a point that they are not putting forward any new solver algorithms. That ok, however, taking existing trainable solvers and assessing how they perform with this guided puzzle generation vs. some other puzzle generation approach is a critical empirical study. Furthermore, it would be helpful to have more discussion of the baseline methods of generating puzzles. When the trainable puzzle solver was originally proposed, how was it trained? Where did the  data come from? How does that compare to this approach. I am not very familiar with this literature, and I imagine this paper would be of interest to folks outside the program synthesis space, so it would be very helpful to better explain this (also we note about related work). There are several additional empirical analysis that could be added to improve this work. For example, for the trainable solver, a plot of (training time) vs (time to solve puzzle) would be interesting. Beyond looking at training time, does a solver trained with the guided puzzle generator end up being a 'better' solver in some way? Are the resulting puzzles harder but still being solved? Is there a way of quantifying the 'hardness' of a puzzle? Perhaps a proxy like size? Then it would be cool to plot (training time) vs (approx puzzle hardness) to demonstrate that . the puzzle generator is really developing a reasonable curriculum.
Finally, there is a bunch of related work that I think is missing. Again, I'm not super familiar with this work, but I think there is a lot of curriculum learning stuff within RL that seems super relevant. Of particular relevance is the Alice/Bob framework from "Intrinsic motivation and automatic curricula via asymmetric self-play" seems very similar to the work at hand.  Something that is interesting in the Alice/Bob framework that could be transferred over here is the notion of the generator wanting to make a puzzle hard, but not too hard, i.e. make it just outside the solvers current capabilities. 
Overall my assessment is that this paper doesn't quite meet the standard for ICLR. My two major critiques are (1) the related work is seriously lacking making it difficult to situate this work in a broader context. The authors also seem to miss the entire curricular learning literature. (2) The empirical evaluations are lacking. In particular, more thorough analysis of how the generator is behaving, the type of curriculum it learns, and the resulting impact this has on a trainable solver all are missing. Furthermore, more focus on trainable solvers would improve this work. 
I'm not an expert in this area so it is possible I misjudged the significance of this work. I'm certainly open to revising my assessment if the authors are able to address (2) in a meaningful way.