Executing OCaml Programs in Eclipse with OcaIDE

This blog post explains how to use OcaIDE to build and run your OCaml Programs. Assuming that you have installed OCaml, Eclipse and the OcaIDE plugin for OCaml, the first step is to setup the right paths to OCaml installation directory in the OcaIDE plugin configuration as shown in the below screenshots.

Once the path to the OCaml directory is set in eclipse you can create a new OCaml Project.The easiest way is to use the "OCaml Empty Makefile Project" type from the New Project Menu in Eclipse.

After creating a new project (say "lab03") right click it in the Navigator menu and click on import to add the files from the assignment in the new project.

Choose File System in the import menu to browse to the files downloaded from IVLE on your disk and check them to be added to this project.

Once you have added the files you can write your "Makefile" to build them. Right click the project and click New File as shown below.

Give the new file the name "Makefile" without any spaces or extension. Enter the following text in the file. The space after the "all:" line is a tab not a series of spaces. For more help about writing Makefile you can check the tutorial.

Once you have the Makefile in your project just right click it and select "Make Project". This would build the corresponding executable (lab03.exe here). If you get some errors make sure you gave the right path to the GNU Make installation in your system in the first step (e.g. C:\cygwin\bin\make.exe).

To execute the file just right click and choose  Run As "Ocaml Executable" as follows.

You should see some output on the console windows. If in the previous step you do not find any "Ocaml Executable" configuration click on the "Run Configurations..." menu item to create a new launch configuration.

Enter the name of the project and the choose the executable file to define a new launch configuration as shown above. Once you add the new configuration you can choose apply and run it. It should now execute with some output on the console window.

List Example for Extracting OCaml from Coq

In this post I will show how to extract a simple list append function written in Coq as OCaml code.

First let us create an inductive type in Coq to define our lists as follows.

Inductive mylist : Type :=

| nil : mylist 

| cons : nat -> mylist -> mylist.

Next, we will define an append function over these lists using the "Function" keyword.

Function myappend (l1:mylist) (l2:mylist) {struct l1} : mylist :=

match l1 with

| nil => l2

| cons x xs => cons x (myappend xs l2)

end.

The append function has a special "struct" which tells Coq that the first argument l1 is the recursive parameter to the function. This is essential as without that Coq will not let you define a function. In this particular case the recursive call is always made on a smaller list thus termination can be proven as an instance of structural recursion. However if we write a function where we want to use more general recursion we have to define a "measure" and prove that it decreases with every recursive call. Once the myappend function is defined in Coq it is easy to state and prove properties about append. The following theorem shows that myappend function is associative. 

Theorem myappend_assoc : forall l1 l2 l3 : mylist , myappend (myappend l1 l2) l3 =

(myappend l1 (myappend l2 l3)).

Proof.

intros.

induction l1.

simpl.

trivial.

simpl.

rewrite IHl1.

trivial.

Qed.

Once we have stated the desired properties and proven their correctness we can also generate OCaml (or Haskell) code from Coq using extraction process. The extraction process will recursively remove the proof terms from the code and convert the program to a corresponding OCaml program. Extraction for the myappend function can be using the following statements in Coq.

Extraction Language Ocaml.

Extraction "mylist.ml" myappend.

The generated code in mylist.ml file looks as below.

type nat =

| O

| S of nat

type mylist =

| Nil

| Cons of nat * mylist

(** val myappend : mylist -> mylist -> mylist **)

let rec myappend l1 l2 =

match l1 with

| Nil -> l2

| Cons (x, xs) -> Cons (x, (myappend xs l2))

The OCaml code extracted from Coq includes all the corresponding data types - nat and mylist used in the program. Also the function myappend is extracted without the proof of termination. Other proof constructs like theorems are also dropped from the extracted code. The extracted code can now be used inside a larger OCaml program.

Using Ocsigen for Web Development with OCaml on Nitrous.IO

As I said in my last post, once you have configured OPAM on nitrous.io, it is quite easy to install additional OCaml libraries and framework. Ocsigen is a web development framework for OCaml. In this post we will see how to configure Ocsigen on nitrous.io to build a simple website with OCaml. To install Ocsigen, just use OPAM

opam install ocsigenserver

After installing Ocsigen we need to install Eliom to enable dynamic websites with Ocsigen. Again run the following command to install it from OPAM.

opam install eliom

If the installations were successful you will now have  a working Ocsigen setup on your machine. In order to test it out let's just create a simple website from the hello world example. Make a new folder in your box inside that copy the following example eliom source file.

 (* ************************************************************************** *)  
 (* Project: Ocsigen Quick Howto : Page                    *)  
 (* Description: Example of a simple page (The famous "Hello World"!)     *)  
 (* Author: db0 (db0company@gmail.com, http://db0.fr/)             *)  
 (* Latest Version is on GitHub: http://goo.gl/sfvvq              *)  
 (* ************************************************************************** *)  
 open Eliom_content  
 open Html5.D  
 open Eliom_parameter  
 (* ************************************************************************** *)  
 (* Application                                *)  
 (* ************************************************************************** *)  
 module Example =  
  Eliom_registration.App  
   (struct  
    let application_name = "example"  
    end)  
 (* ************************************************************************** *)  
 (* Service declaration                            *)  
 (* ************************************************************************** *)  
 let main =  
  Eliom_service.service  
   ~path:[]  
   ~get_params:unit  
   ()  
 (* ************************************************************************** *)  
 (* Service definition                             *)  
 (* ************************************************************************** *)  
 let _ =  
  Example.register  
   ~service:main  
   (fun () () ->  
    Lwt.return  
      (html  
        (head (title (pcdata "Hello World of Ocsigen")) [])  
        (body [h1 [pcdata "Hello World!"];  
            p [pcdata "Welcome to my first Ocsigen website."]])))  

In my box I saved this file as the example/example.eliom. Then I created example/static folder to host the static resources of the website. In order to build this file you can use the magic makefile provided by Ocsigen. Change the static dir to "./static" and  in server files put "example.eliom" , in addition I had to remove the "-noinfer" option from the file as the compiler was giving an error with it. Once you make these changes you can compile your eliom web application example.eliom by typing "make" on the console. It will create a directory structure as follows in the same directory.

The compiled web application is "example.cma". Now we need to launch the Ocsigen server with this web application. For that we take help of the following conf file. 

 <!-- ----------------------------------------------------------------------- -->  
 <!-- Project: Ocsigen Quick Howto                      -->  
 <!-- Description: Configuration file to launch the examples         -->  
 <!-- Author: db0 (db0company@gmail.com, http://db0.fr/)           -->  
 <!-- Latest Version is on GitHub: https://github.com/db0company/Gallery/   -->  
 <!-- ----------------------------------------------------------------------- -->  
 <ocsigen>  
  <server>  
   <port>3000</port>  
   <logdir>./tmp/</logdir>  
   <datadir>./tmp/</datadir>  
   <user></user>  
   <group></group>  
   <commandpipe>./tmp/ocsigen_command</commandpipe>  
   <mimefile>/home/action/.opam/4.01.0/etc/ocsigenserver/mime.types</mimefile>  
   <extension findlib-package="ocsigenserver.ext.ocsipersist-sqlite">  
    <database file="./tmp/ocsidb"/>  
   </extension>  
   <extension findlib-package="ocsigenserver.ext.staticmod"/>  
   <extension findlib-package="eliom.server"/>  
   <charset>utf-8</charset>  
   <debugmode/>  
   <host hostfilter="*">  
    <static dir="./static/" />  
    <eliom module="./example.cma">  
    </eliom>  
   </host>  
  </server>  
 </ocsigen>  

Save the above file as "example.conf" in the same directory and launch the server with the following command.

ocsigenserver -c example.conf 

 This is configure the server to run on the 3000 port as specified in "example.conf" and run the example application. You can test that the application is running using the Preview feature on nitrous.io.

Just use the 3000 port and then the web server should serve the following page in a new window.

This enables nitrous.io to be used as a web development environment for OCaml.  You can now use the Web IDE to develop web applications for OCaml in the same way as you can do for the default boxes supported by nitrous.io. 

Configuring OPAM for OCaml on Nitrous.IO

In the previous post I showed how to get a working OCaml compiler installed on a nitrous.io box.  We had to get the source code of OCaml from github and build it. It turns out there is a much easier way to get the compiler and all the necessary libraries. We can install the OPAM package manager inside our box and then use OPAM to download additional libraries. In order to configure OPAM on nitrous.io we follow the steps on the quick install page  for the binary installer of OPAM. Run the following commands in the terminal.

wget http://www.ocamlpro.com/pub/opam_installer.sh 

sh ./opam_installer.sh /home/action/.local/bin

The installer will guide you through the process of setting up and installing the OCaml compiler. Once the installation finishes you can use the OCaml system from console. You can also use OPAM to install additional libraries. Details on the usage of OPAM as a package manager are given here. By default it OPAM will install the libraries shown in the screenshot below.

OCaml on Nitrous.IO

Nitrous.IO provides free servers with console access to developers. The servers can be provisioned across different geographies and allows for a good way to code on the web. Each nitrous box comes with a web based IDE and console access. They provide boxes for web development in Ruby/Rails, Go, Python/Django and node.js. However since they allow console access it is possible to install many other systems on your nitrous box. It can be used as a good way to do we based tutorials or small projects inside the box as well. The web based IDE also has experimental support for collaboration so it can be a good tool to work on some project together with others. In this post I will show how to install OCaml on Nitrous so that you can code and test simple OCaml programs. It can be ideal for class assignments or small projects since the OCaml compiler is not the easiest thing to install on Windows and Mac platforms (based on my experience of teaching a class of undergrads). 

To begin, register on nitrous.io and create a new box, you can choose any of the default box but I chose python. Give it some name (dev-box) and chose the region closest to you (Southeast Asia).

Once you create a box you should be logged into the web based IDE on the box with console at bottom as shown below.

We will use the console to download and install the OCaml compiler. You can use the source code from the OCaml github repository. Just clone the source code using the https url to the repository. ("git clone https://github.com/ocaml/ocaml.git") 

It will create an ocaml directory with all the source code in your workspace. Change to that directory and then run "./configure -prefix /home/action/.local" This will tell the compiler to install in your local user directory under .local folder. 

Once the configuration finishes successfully, we can use "make world.opt" to build the compiler and "make install" to install it. (Look up INSTALL file in the ocaml directory for more detailed notes on installation. It is pretty standard way of  building the compiler on a linux machine.)  If you followed the steps without errors you will now have a working OCaml compiler on your nitrous box. You can run the OCaml toplevel by running "ocaml" from your workspace. Additional OCaml libraries like findlib can also be installed by using wget command to get the source code from their website and building them. 

You can use the web based IDE provided with your nitrous box to edit OCaml programs and run them using the console.

As you can see above I am using C for syntax highlighting as the web IDE doesn't support OCaml yet. The setup is not perfect but it allows anyone to try OCaml on the web without much fuss and hey its free !!! I actually managed to run all the lab assignments and tutorials for the module I am TAing this semester at NUS.