I moved to http://yansh.github.io

 http://yansh.github.io

Fixing an exception while installing ghostscript on MacOS X using macports

If you ever encountered the following exception while installing ghostscript using macports:

--->  Verifying checksums for ghostscript

Error: org.macports.checksum for port ghostscript returned: ghostscript-fonts-other-6.0.tar.gz does not exist in /opt/local/var/macports/distfiles/ghostscript

Error: Failed to install ghostscript

 The solution is very simple.

Simply download the missing file from here and place it manually in

/opt/local/var/macports/distfiles/ghostscript

This should fix it.

It took me awhile to find it and I would like to thanks this thread to pointing me to the right answer.

Installing OCaml for MacOS Noobie!

After successfully installing OCaml and Ocaide plugin for Eclipse on a  Mac, I now think it's straightforward, however, before I completely forget the pain involved in figuring out what goes where. I wanted to put down some pointers for noobies like me, in hope that it will save people some valuable time.

In general, ocaml.org is a great spot for finding any information related to OCaml. Installing OCaml is no different, you can read all about it here. There is tons of very useful and detailed information that I highly recommend anyone who is interested in OCaml to check out. In this post I just summarize the steps it took me to get from zero to OCaml installed (hero!).

Feel free to correct me or share your own personal successes and experiences.

The following steps worked for me:

• Install Homebrew

• Install Xcode (check this guide)

xcode-select --install

• brew install ocaml 

• brew install opam - I encountered a problem and apparently I am not the only one - see details and solutions here.
• Basically if after installing opam and trying to run it, you get "Illegal instruction: 4"  Try running:

 brew reinstall --build-from-source opam

you can thank @avsm for the workaround.

Now that you have OCaml installed, let's discuss IDEs.

IDEs

Eclipse 

My IDE of choice is Eclipse¹ ocaide plugin very useful. I used it on Ubuntu and thought that installing it on Mac might be a good way to go.

There are multiple guides (from Upenn, JSU) on the web on how to do just that, just make sure that you get all the prerequesite components such as Java 7 installed and ready to go.

Upenn CS120 provides a nice list for you to follow, make sure that you do! - thanks guys!

1. Mac Users Only Install X11 libraries (needed for the OCaml graphics libraries to work):
• Install Apple's XQuartz version, which is available here: http://xquartz.macosforge.org/landing/
• Before moving on to the next step, make sure you LOG OUT of your user account so that the X11 install can complete.
• Check to see that the directory /usr/X11/lib exists and that it contains the file libX11.6.dylib (this should have been created when you installed XQuartz). If this isn't the case, try reinstalling XQuartz and then contact the course staff for help.
• [MM] Removed these instructions, because ~/lib isn't on the default PATH for Macs, and because with most recent SW updates this step isn't necessary.
• From the terminal, in your home directory (e.g. /Users/stevez) create a directory called lib (if one does not already exist):

   > cd > mkdir lib 

• Create a symbolic link in that lib directory to the libX11.6.dylib file:

   > cd ~/lib > ln -s /opt/X11/lib/libX11.6.dylib libX11.6.dylib 

• Next, install the Java Development Kit (JDK) 7. You can download it from this this site (after accepting the terms & conditions). Make sure you do this step before installing Eclipse or OCaIDE.

[Update] As was pointed out by numerous stackoverflow posts like this one , Eclipse IDE tend not to recognise environment variables. The solution is to wrap the execution into a bash script. It works, however, I couldn't manage to make it work with the MacOS launch database. Even after the update of the Info.plist, Eclipse still won't recognise environment variables. At this stage, I run the script manually and it works.

Vim 

[Update] VIM grows on me. If you are interest to configure VIM to use OCaml, please follow these instructions by @avsm.

Here is how my ~/.vimrc looks like:

execute pathogen#infect()

let s:ocamlmerlin=substitute(system('opam config var share'),'\n$','','''') .  "/ocamlmerlin"

let g:syntastic_ocaml_checkers = ['merlin']

au BufRead,BufNewFile *.ml,*.mli compiler ocaml

execute "set rtp+=".s:ocamlmerlin."/vim"

execute "set rtp+=".s:ocamlmerlin."/vimbufsync"

execute ":source " . "/Users/Yan/.opam/system/share/vim/syntax/ocp-indent.vim"

You can then do some cool stuff as kindly shared here by Thomas Leonard:

Then you get some nice shortcuts:

• \s switches between the .ml and .mli file
• \c comments the current line / selection (\C to uncomment)
• % jumps to matching let/in, if/then, etc (see :h matchit-install)
• \t tells you the type of the thing under the cursor (if you compiled with -annot)

Thomas also adds

"Also, Vim can then parse the output of the compiler and jump to the correct location."

However, he doesn't say how to do that. I searched the web and eventually figured it out. So here is what you need:

1. Makefile to compile you code
2. Vim 7.4+ (earlier versions don't seem to support it.
3. and the knowledge how to use vim's quickfix

Let's tackle these one by one:

1. Here is a sample of a Makefile:

NAME =

OCAMLBUILD = ocamlbuild -use-ocamlfind  -classic-display

PACKAGES = -package -tag thread

all:

                $(OCAMLBUILD) $(PACKAGES) filename.byte 

clean:

                rm *.byte

test:   

                $(OCAMLBUILD) $(PACKAGES) filename.byte 

2. Make sure you have an updated version of Vim.

3.  You can read the full documentation on it here, or check this quick and what I thought I useful, summary provided by this stack overflow answer - run: make and then:

:copen " Open the quickfix window
:ccl   " Close it
:cw    " Open it if there are "errors", close it otherwise (some people prefer this)
:cn    " Go to the next error in the window
:cnf   " Go to the first error in the next file

That's all folks! Enjoy.

Please let me know if above helped you or you whether you encountered other issues so I can update the post accordingly.

¹ After some issues with PATH variables in Eclipse, I am seriously considering converting to Vim.

Work summary @ OCaml labs

In this blog I would like to summarise my contribution to some of the on going projects as well as highlight some of the open source development that I encourage the wider community to adopt and provide feedback.

First, I would like to acknowledge the incredible support and welcome I received from the OCaml labs  - lead by @avsm. Thank you for facilitating great and fun working environment.

Executive summary

My main contribution involved

1. Research and development of a graph-based service abstraction for PIH as part the UCN project.

Deliverables: 

• Co-authored a whitepaper (draft) on how Moana-based service abstraction can be used to facilitate access control

• MoanaML - OCaml implementation of Moana
• The repository also contains an  implementation of the RETE algorithm
• Developing contacts app (OCaml code) to showcase PIH features as well as how graph based-service abstraction can be used to build applications. 
• A few blog posts

2. Contributing to Ocaml.org - creating a teaching resource page  for the community which provides useful resources for people who would like to keep up to date with the relevant material and resources for teaching OCaml to masses, mainly at the Uni level.

3. Pubłished a position paper (Moana - A Case for Redefining the Internet Service Abstraction) Middleware for Next Generation Internet Computing (MW4NG).

Besides stated above contribution, I was able to participate and help organise in many interesting initiatives such as help set up with @amirmc start-up class meet ups for people to follow online Stanford course on "How to start a startup" as well participated in (initial) discussions with the Office of Postdoctoral Affairs to setup the first Cambridge postdoc's entrepreneurial club. I also learnt a lot about very exciting technologies being developed around the lab such as Mirage OS, Irmin, Jitsu and many others (here is the 2014 review)

Now, in more details...

While in OCaml labs my main role involved contributing to research and development of a personal information hub (PIH) as part of the UCN project. The main objective of the project is:

"... to develop and use the PIH platform and architecture to install the user as the owner and controller of his/her personal data, allowing personalization and immersion while preserving a user’s privacy."

This is an on going project with very promising outcomes and I believe that the technology developed as part of it can serve as the foundation for future information-centric systems. ''

The current two main building blocks are Mirrage OS for deployment and Irmin for Git-like persistent storage. Both very interesting system which I recommend to check them out.

After learning more about the project, I felt that it's very important to provide a very useful and efficient service abstraction for application and system developers to use in order to simplify the development on top of such a systems.

Enter Moana. Moana, an information-centric middleware for distributed services and applications. Moana offers a shared graph-based storage abstraction through which applications communicate with each other by appending and observing the shared graph. Arguably, this higher level of abstraction is much closer  to the developer world, which "allows developers to focus their efforts on functionality and spares their time fiddling with low level tasks, such as information synchronisation or storage". Applications can also specify access control policies which can be then enforced by the system. It would be great to see Moana like abstraction on top of Irmin which I believe will move the overall design  closer towards the overall goals of the UCN project.

So the main challenge was to develop and deploy Moana on top of Irmin. Both Mirage OS and Irmin (for many good reasons ) are written in OCaml so naturally I had to learn OCaml. This is how the work on MoanaML started. MoanaML is essentially implementation of Moana in OCaml. During the process I learnt a lot about type safe, functional languages and at this stage, this paradigm aligns extremely well with  Moana's AC mechanisms (I am working on the blog about it).

The current MoanaML has a couple of implementations including one for Irmin. I previously blogged about it.

I was also working on showcasing the the power behind MoanaML  and the ideas behind a PIH-type applications by developing a contacts app prototype. I will have a separate blog about it soon. In a nutshell, I developed contacts app which uses MoamaML code to store all contacts in the Moana graph, which also contains various access control policies for various requesters. Using js_of_ocaml I converted the contacts app (backend) code into JS which allowed me to reuse it in the JavaScript app development framework such as AngujarJS. I then used Ionic framework which translates JS apps to native mobile apps to create the front end. The current implementation requires further testing and development, nevertheless, the current ability to deploy OCaml code on the phone with nice native app like user interface, I believe, serves as a nice substrate for further for it.

2. I helped out to setup the Ocaml teaching resource page for the OCaml.org website.  The page contains resources for teaching OCaml. It also gathers information on where OCaml is currently being taught.

3. Read the paper :)