Saturday, September 27, 2014

GHCID - a new GHCi based IDE (ish)

Summary: I've just released ghcid, which interactively shows the errors in your project on each save.

I'm please to announce ghcid, which is either "GHCi as a daemon" or "GHC + a bit of an IDE". I've been using it for my development for the last few days, and already find it quite valuable. Unlike other Haskell development tools, ghcid is intended to be incredibly simple. In particular, it doesn't integrate with any editors, doesn't depend on GHC the library and doesn't start web servers. It's under 200 lines of fairly dull Haskell, which talks over pipes to your existing ghci.

Using it

Run cabal update && cabal install ghcid to install it as normal. Then run ghcid --height=10 "--command=ghci Main.hs". The height is the number of lines you are going to resize your console window to (defaults to 8), and the command is how you start this project in ghci. Personally, I always create a .ghci file at the root of all my projects, which usually reads something like:

:set -fwarn-unused-binds -fwarn-unused-imports
:set -isrc
:load Main

With that you can pass --command=ghci (or nothing, since that is the default).

After that, resize your console and make it so you can see it while working in your editor. On Windows the ghcid console will automatically sit on top of all other windows. On Linux, you probably want to use your window manager to make it topmost or use a tiling window manager.

What you get

On every save you'll see a list of the errors and warnings in your project. It uses a single ghci under the hood, so even relatively large projects should update their status pretty quickly. As an example:

    Not in scope: `verbosit'
    Perhaps you meant `verbosity' (imported from System.Console.CmdArgs)
Util.hs:18:1: Warning: Defined but not used: `foo'

Or, if everything is good, you see:

All good

This project is only a few days old, so please report any bugs you find.

What you want

I regularly use an IDE to develop in a Haskell-like language. I find that with the IDE I'm about 25% more productive than without it. While an IDE can provide lots of neat features (go to definition, search, type tooltips) I think most of the productivity gains come from:

  1. Syntax coloring.
  2. A list of errors and warnings...
  3. ...which is updated as you type...
  4. ...and are highlighted in the text (red squiggles).

Every text editor already provides syntax coloring. With ghcid you get the list of errors and warnings. To get the final two features you need to integrate with an editor. I'm hoping that ghcid can do some of the heavy lifting by taking a directory of files to treat as overrides, and producing a list of warnings/errors to a file. The rest is editor specific, and I hope to attempt integration with Sublime Text at some point (although would love some help).

Wednesday, September 24, 2014

Generating Open 3D Viewer Models

Summary: It's not obvious how to generate suitable Open 3D Viewer models, but with the right tools it isn't hard.

The Open 3D Viewer project is very cool, as an example here is a demo of a spinning cow rendered in the browser. For my wife's work I wanted to generate a 3D model of a fossil bedding plane. Effectively, given some x/y/z coordinates, produce a pretty rendering. It took a fair bit of guess work, so I wrote down the steps.

Step 1: Generate an OBJ file

Generate an OBJ file. You probably want an MTL file too, but it seems the 3D viewer only uses the Kd field. There are a few ways to get an OBJ file:

  • There are many samples on the web, including a snail in the Open 3D Viewer repo.
  • You can create OBJ files in a tool such as Blender, but the Blender interface confused me a lot (I am definitely not their intended audience).
  • You can generate an OBJ file using a Haskell script. I picked this method, and I'll write a blog about the script later, once I have some pretty pictures to show.

Step 2: Get the tools

There are some tools in the WebGL Loader project. Alas, that project says "for now I recommend r50 as the last stable revision". So now there are two tools to try, the latest and r50. I tried both. I had some limited success with r50 (it didn't seem to render properly, but it did run) while the latest revision segfaulted. Fortunately I found the tools in a Google Groups post, and have mirrored them in my repo (with trivial tweaks to support Python 2.7).

Step 3: Run objcompress

You need to run:

objcompress mymodel.obj mymodel.utf8 > mymodel.js

This will generate lots of mymodel*.utf8 files and mymodel.js.

Step 3: Run

You need to run:


(The file in the email is part&, but I renamed my copy.) This script will interactively ask a really long list of questions. I generate the correct inputs into a file and pipe it in:

py < response.txt

This generates the files groupings.txt and part_info.txt.

Step 4: Run



This generates the file entity_metadata.json.

Step 5: Get the viewer source

You can get the viewer source from the Open 3D Viewer repo. I have mirrored it in my repo, but I may tweak the viewer over time to match my wife's needs - you should get the original.

Step 6: Copy your files

Copy all the files from steps 1 to 4 to a directory inside the viewer named models/mymodel.

Step 7: Update the model list

Open up scripts/models.js and edit it to point at your model. For example:

o3v.MODELS = [{

Step 8: View the result

You can view the result by opening index.html. In Chrome you may need to pass the flag --allow-file-access-from-files.

Tuesday, September 16, 2014

Towards Shake 1.0

Summary: I've just released a new version of Shake, with a --demo feature and an underlying continuation monad. I want to release v1.0 in the near future.

I've just released a new version of the Shake build system, version 0.13.3. While the version number is only 0.0.1 higher, the changelog lists a large number of improvements. In particular, two changes are:

  • The Action monad is now based on continuations, which allows Shake to suspend threads without requiring a GHC RTS thread. The result is significantly less memory used on thread stacks. I still find it quite amazing that Haskell has such powerful and robust abstraction mechanisms that a huge change doesn't even break the API.
  • The shake binary now features a --demo mode, invoked by running shake --demo. This mode generates a Shake project, compiles it, and shows off some of the features of Shake. You can the output of --demo here.

Version 1.0

With the two features above, I'm now looking towards Shake version 1.0. I'm not looking to make any significant backwards-incompatible change, or necessarily any code/API changes at all. However, if you have anything you think should be addressed before reaching such a milestone, please comment on the issue tracker or email the mailing list.

Shake website

The one thing I still want to finish before releasing version 1.0 is to have a proper website for Shake. I've registered which will host the content, and have set up GitHub pages to serve it up. I have some rough content in the docs directory and a prototype generator in the website directory - as an example it currently generates something a bit like this for the user manual, but with a table of contents when run through the latest generator. I'd appreciate any help with the content, the generator, or the styling - just email the mailing list.

Sunday, September 07, 2014

Shake in the wild

Summary: I spotted a few things using Shake, which I had nothing to do with.

In the past few days I have come across several things using the Shake build system. I wasn't involved in any of them, and haven't (yet) tried any of them out, but they certainly look cool.


Tibor Bremer from Utrecht University gave a talk at the Haskell Implementors Workshop 2014 about his ToolCabal project. This project replaces the "build a package" part of Cabal with something more flexible, supporting multiple simultaneous targets and more flexible preprocessors - all built on top of Shake. It doesn't attempt to tackle dependency resolution yet. There is a video of the talk:


The folks at Samplecount have written several Shake based things. None are yet on Hackage, so I suspect they are somewhat prototypes, but they look like they're already used quite seriously.

  • shake-cabal-build to make it easier to build your Shake build systems with Cabal. Shake build systems need to be compiled with GHC, for which I usually use ghc --make, but this project explains how to get things building with Cabal - important if your build system pulls in other libraries.
  • shake-language-c is a project to simplify building C/C++ projects with Shake. From the docs:

shake-language-c is a cross-platform build system based on the Shake Haskell library. The focus is on cross-compilation of C, C++ and Objective C source code to various target platforms. Currently supported target platforms are iOS, Android NDK, Google Portable Native Client, MacOS X, Linux and Windows (MinGW). Supported host platforms are MacOS X, Linux and Windows.

  • methcla is their mobile sound engine, which is built using this Shake script, which (unsurprisingly) uses shake-language-c and shake-cabal-build.