Saturday, December 08, 2018

A little RPG in React Native

I built a little role-playing game in React Native. I tried to build the type of game I like playing, with quests and interactions with non-playing characters, while learning some mobile UI programming tricks.  These are some of the main points that I took away:

  • The initial setup was a bit involved, probably because I'm not used to develop JavaScript applications. Getting the right code to properly do the plumbing between React, Redux,  React Navigation, tests, etc. was a bit of a hassle. Obviously this has to be done once and then you can concentrate on writing the functional code. As I noted recently, then upgrading to newer versions of your dependencies can be a hassle!
  • I was happy with my declarative approach to the game world. I don't think it would be manageable to do otherwise.  I define as JavaScript structures the world itself: the different places and how they communicate, the items they contain, etc., the non-playing characters and the possible interactions you can have with them, items and their characteristics, monsters and spells. This gives me an immutable representation of the start world, and the state of an actual game just has to store the modifications from that initial state
  • This of course could mean that I (or somebody else) could reuse the game mechanics for a totally different adventure!
  • I of course used of Redux to manage state. The state is only modified by Redux reducers, so everything the player does in the UI just becomes actions, not explicit state management operations. I combine several reducers, each reducer being responsible for modifying one section of the global state, which makes each reducer simpler, but fragment the code. For example when the player takes an item from a room, one reducer adds the item to the inventory, another removes the item from the room, so maybe there's some potential for bugs there
  • I found the integration between React and Redux easy to use: you simply define the mapping between the state and components properties, and between component interactions and Redux actions.
  • I abused a little bit Redux to implement combat: combat holds a kind a mini state for each fighting round, and then the result of a fighting round both is represented in the UI ("the rats bite you for 2 damage"), and impacts the global world.
  • I didn't spend too much time on the UI, just using basic React Native components. I found some of the layout hard to do correctly, and styling components is not intuitive when you're not a CSS expert. Maybe I should take a CSS/Design course, because you can tell from my UI designs that I'm a programmer :-)
  • All in all, writing in modern JavaScript was nicer than expected, even though I think using a stronger typed language would be better. If I had to do another similar project I would probably try to use Typescript. I liked especially the object spreads to update parts of structures and the use of consts.
  • I used Expo to test on a tablet, I didn't try to actually generate a final application outside of Expo, I haven't looked at all on how to distribute the game as an app.

All in all, if was an enjoyable experience, but of course designing a full game instead of just a prologue you can do in 5 minutes would be a different type of endeavor...

Tuesday, December 04, 2018

Fun with NPM and Expo

Some time ago, I wrote a little game using React-Native so I could play around in Javascript with React, Mobile development and Redux. Yesterday I checked this project again on Github, and saw that there was a security issue Github detected and warned me about: the "merge" library had a vulnerability, reported in CVE-2018-16469. OK, time for action!
Of course, my project doesn't reference merge directly. It's a transitive dependency of jest. A quick check on the web showed that since I created the project, a lot of things have happened, so my project dependencies are lagging behind. So hopefully upgrading should solve my security issue.
I find instructions at, so I run npm outdated, which indeed confirms a lot of my dependencies are old.
I install npm-check-updates:
npm i -g npm-check-updates
ncu -u
As indicated, and I get:
Hmmmmm... this is taking a long time. Your console is telling me to wait for input on stdin, but maybe that is not what you want.
Try specifying a package file explicitly with --packageFile package.json.

OK, then:
ncu -u --packageFile package.json

This updates everything, and then my app doesn't start anymore. Turns out a lot more changes have happened when I wasn't looking, and the react native starter app I created has now changed to use expo-cli. I find some instructions on how to change the npm scripts, but it doesn't solve everthing, I still get an error in the react-native-scripts main file, because the main entry also needs to be changed (thanks Then it stills fails because the babel module has been renamed, thanks to And then on my expo client I get a Javascript mismatch error, that helped me solve...

OK, now my game starts again, I suppose I need to test it thoroughly because something may again decide to break... I did enjoy developing the game, but certainly managing the NPM vulnerabilities and the Javascript ecosystem pace of change can be challenging. I know this isn't an original thought, but experiencing it first hand is definitely an eye-opener!

Monday, December 03, 2018


Whoa, nearly two years since I last put something on this blog. I lost the habit, and since I'm not involved in EclipseFP anymore I don't have the stream of Haskell news to report I used to. I will now try to reboot it and try to find interesting experiences to share!

I was never a big fan of social media sites, but I use to link to some of these blog posts on Google +, which is now dying. So this should stay a simple blog, where I have nothing to sell you and no ads to pester you with!

Over the last few months I've built a toy project in React Native, started learning Go, and done a lot of things in my day job, so hopefully some interesting stories will appear! Stay tuned!

Saturday, January 21, 2017

So long Haskell, and thanks for all the functional fish

I've realized I haven't written or read a line of Haskell in the past 6 months. After roughly ten years of tinkering with it, it seems that I've given up on it. There is a big obvious reason, and other smaller ones.

Professionally, my job got a lot more challenging (I'm officially an **architect** now, which means I still write lots of code but I have to draw pretty diagrams too (-: ) and involves a lot of research and learning new stuff, things like microservices, docker, messaging, Angular2, mobile apps, etc. So a lot of my time is dedicated to work or to learning for work, so I don't have the time to play around with something quite unrelated like Haskell.

I suppose to be honest there also was a bit of lassitude with Haskell. I got tired of the less than optimal IDEs, I realized Haskell was not going to get me a great job, and there were a few little skirmishes on the web that got ugly and made me see the community in a less favorable light.

This was fun, though, and I certainly learned a lot, and I hope it has made me a better programmer. A lot of my coding now is done in Java 8, and it's good to be able to apply some functional idioms practiced in Haskell, and more general ideas like data immutability, small pure functions do help make better - more testable, easier to understand - code.

So maybe I'll come back to Haskell some day, but not for now. To all the open source projects I've contributed, I wish you the best!

Happy Haskell (or any other language) Hacking!

Saturday, October 01, 2016

Everything is broken

This week was I suppose fairly typical. Started using a new library, the excellent sqlg that provides the TinkerPop graph API on top of relational databases. Found a bug pretty quickly. Off we go to contribute to another open source project, good for my street cred I suppose. Let’s fork it, and open the source code in IDEA (Community edition). After years of hearing abuse about Eclipse, I’m now trying to use “the best IDE ever” (say all the fan boys) instead. Well, that didn’t go so well, apparently importing a Maven project and resolving the dependencies proves too much for IDEA. I fought with it for a while, then gave up.

Fired up Eclipse, it opened and built the sqlg projects without a hitch. Wrote a test, fixed the bug, raised a PR, got it accepted with a thank you, life is good.

Then I find another bug. Except that upon investigation, it’s not in sqlg, it’s in the actual TinkerPop code. The generics on a map are wrong, there are values that are not instances of the key class (thanks generics type erasure!). So I can fix by changing the method signature, or change the keys. Both will break existing code. Sigh…

Oh, and the TinkerPop project doesn’t build in Eclipse. The Eclipse compiler chokes on some Java 8 code. Off to the Eclipse bug tracker. Maybe I need to have three different Java IDEs to be able to handle all the projects I may find bugs in.

Everything isbroken. Off I go to my own code to add my own bugs.

Wednesday, August 03, 2016

Scratching an itch: generating Cabal data-files field automatically

Maybe I didn't look hard enough, but I'm not aware of a tool to generate the contents of the Cabal data-files field automatically when you have loads of folders to include. Cabal has very simple wildcard matching for files references in this field, by design (to avoid including too much data in a source distribution). So it only supports wildcards to replace the file name inside a directory for a given extension, and doesn't support sub directories.

For the reload project - first release on Hackage! - I had to include loads of files, all the Polymer web components the UI depends on, which are all on different sub directories, with a bunch of different extensions. So I wrote a little tool to generate the field automatically, and put it on Hackage too.

You pass it a directory name, possibly some subdirectories and extensions to ignore, and it generates all the required entries. Saved me loads of time, and scratched my own itch!

Saturday, July 16, 2016

Another Web-based Haskell IDE

After giving up on EclipseFP, I've worked a bit on haskell-ide-engine and leksah, contributing little things here and there to try to make the Haskell IDE ecosystem a little bit better. But at some point, I tried to update the GTK libraries on my Ubuntu machine to get leksah to run, and broke my whole desktop. Hours of fun followed to get back to a working system. So I thought again at my efforts last year to have a web based IDE for Haskell, because using the browser as the UI saves users a lot of pain, no UI libraries to install or update!

I started another little effort that I call "reload", both because it's another take on something I had started before and of course because it issues ":reload" commands to ghci when you change files. I have changes the setup, though. Now I use Scotty for the back end, with a REST API, and I use a pure Javascript front-end, with the Polymer library providing the web component framework and material design. I also use a web socket to send back GHCi results from the back end to the browser. I still use ghcid for the backend, maybe one day when haskell-ide-engine is released I can use that instead.

The functionality is fairly simple yet: there is a file browser on the left, and the editor (I'm using the ACE web editor) on the right. There is no save button, any change is automatically saved to disk (you use source version control, right?). On the server, there is a GHCi session for each cabal component in your project, and any change causes a reload, and you can see the errors/warnings in a menu and in the editor's annotations. You can build, run tests and benchmarks, and I've just added ":info" support. The fact that we're using GHCi makes it fast, but I'm sure there's loads of wrinkles to iron out still.

Anyway, if you're interested in a test ride, just clone from Github and get going!