Previous week Up Next week


Here is the latest Caml Weekly News, for the week of February 12 to 19, 2008.

  1. Sydney (Australia) Functional Programming Group
  2. New release of moca
  3. GLCaml version 20080215 available

Sydney (Australia) Functional Programming Group


Erik de Castro Lopo announced:
I'd like to announce the FP-SYD, the Sydney (Australia) Functional
Programming group. The intro page is here:

To subscribe to the mailing list (mainly for meeting organisation,
meeting announcements, and Sydney job offers) either go to the URL
above of send mail to:

  fp-syd-subscribe at googlegroups dot com

New release of moca


Pierre Weis and Frédéric Blanqui announced:
            Relational types in Caml

We are pleased to announce the 0.5.0 version of Moca, a general construction
functions generator for relational types in Objective Caml.

In short:
 Moca allows the high-level definition and automatic management of
complex invariants for data types; Moca also supports the automatic generation
of maximally shared values, independantly or in conjunction with the 
declared invariants.

Moca's home page is
Moca's source files can be found at

Moca is developped by Pierre Weis and Frédéric Blanqui, Richard Bonichon and
Laura Lowenthal (see the file AUTHORS in the main directory of the

In long:

 A relational type is a concrete type that declares invariants or relations
that are verified by its constructors. For each relational type definition,
Moca compiles a set of Caml construction functions that implements the
declared relations.

Moca supports two kinds of relations:
- algebraic relations (such as associativity or commutativity of a binary
- general rewrite rules that map some pattern of constructors and variables to
 some arbitrary user's defined expression.

Algebraic relations are primitive, so that Moca ensures the correctness of
their treatment. By contrast, the general rewrite rules are under the
programmer's responsability, so that the desired properties must be verified
by a programmer's proof before compilation (including for completeness,
termination, and confluence of the resulting term rewriting system).

What's new in this release ?

* Lot of work on the documentation: a research paper has been published to
 described the framework at ESOP'07, talks about relational types and the
 internal of the compiler are included in the distribution.

* An automatic test generation facility has been developped to test the
 specifications written in Moca.

* Arbitrary Caml code can be written in the .mlm files (any sequence of Caml
 signature items are allowed as extra algebraic properties of
 generators). This ``external'' code is included as is in the resulting 

* Commutativity relation gets an extra argument which gives the order used to 
 sort the combs (or lists in case of a vary-adic generator).

* Source code of the compiler has been documented.

* No more shell scripts: the compiler is entirely written in Caml.

* User's defined rules have been generalized from pattern -> pattern
 to pattern -> expr.

An example

The Moca compiler (named mocac) takes as input a file with extension .mlm
that contains the definition of a relational type (a type with ``private''
constructors, each constructor possibly decorated with a set of invariants or
algebraic relations).

For instance, consider peano.mlm, that defines the type peano with a binary
constructor Plus that is associative, treats the nullary constructor Zero as
its neutral element, and such that the rewrite rule Plus (Succ n, p) -> Succ
(Plus (n, p)) should be used whenever an instance of its left hand side
appears in a peano value:

    type peano = private
       | Zero
       | Succ of peano
       | Plus of peano * peano
         neutral (Zero)
         rule Plus (Succ n, p) -> Succ (Plus (n, p))

From this relational type definition, mocac will generate a regular Objective
Caml data type implementation, as a usual two files module.

From peano.mlm, mocac produces the following peano.mli interface file:

    type peano = private
       | Zero
       | Succ of peano
       | Plus of peano * peano
    val plus : peano * peano -> peano
    val zero : peano
    val succ : peano -> peano

mocac also writes the following file that implements this interface:

    type peano =
      | Zero
      | Succ of peano
      | Plus of peano * peano

    let rec plus z =
      match z with
      | Succ n, p -> succ (plus (n, p))
      | Zero, y -> y
      | x, Zero -> x
      | Plus (x, y), z -> plus (x, plus (y, z))
      | x, y -> insert_in_plus x y
    and insert_in_plus x u =
      match x, u with
      | _ -> Plus (x, u)
    and zero = Zero
    and succ x1 = Succ x1

To prove these construction functions to be correct, you would prove that
 - no Plus (Zero, x) nor Plus (x, Zero) can be a value in type peano,
 - for any x, y, z in peano. plus (plus (x, y), z) = plus (x, plus (y, z))
 - etc
 Hopefully, this is useless if mocac is correct: the construction functions
 respect all the declared invariants and relations.

To prove these construction functions to be incorrect, you would have to
 - find an example that violates the relations.
Hopefully, this is not possible (or please, report it!)

And, if you needed maximum sharing for peano values, you just have to compile
peano.mlm with the "--sharing" option of the mocac compiler:

$ mocac --sharing peano.mlm

would do the trick !

Moca is still evolving and a lot of proofs has still to be done about the
compiler and its algorithms.

Anyhow, we think Moca to be already usable and worth to give it a try.
Don't hesitate to send your constructive remarks and contributions !

GLCaml version 20080215 available


Elliott Oti announced:
GLCaml version 20080215 is now available at

GLCaml is a collection of three modules:

1. Glcaml, which offers dynamic bindings to OpenGL 1.1 through 2.1 plus all 
ARB and vendor specific extensions.

2. SDLCaml, which offers bindings to SDL (, a graphics 

3. Win, which allows OpenGL calls to be used from an Ocaml Graphics window
without requiring other libraries such as SDL or GTK.

This version of GLCaml has major API changes with respect to the previous
versions. The following changes have been made:

1. Bigarrays are no longer necessary for using OpenGL functions. Standard
Ocaml types (ints, floats, bools and strings, and corresponding arrays) are
now used.

2. Enumerated constants (glenums) have been replaced by ints. As a result,
there are no more GL_ALL_CAPS constants; these have been replaced by
gl_no_caps ints

3. An exception is now always thrown if an OpenGL call is not available. This
is because silent fails can leave mutable parameters in an undefined state.

Extra examples have been added that make use of the Win module, including an 
example demonstrating the use of OpenGL shaders.

Using folding to read the cwn in vim 6+

Here is a quick trick to help you read this CWN if you are viewing it using vim (version 6 or greater).

:set foldmethod=expr
:set foldexpr=getline(v:lnum)=~'^=\\{78}$'?'<1':1

If you know of a better way, please let me know.

Old cwn

If you happen to miss a CWN, you can send me a message and I'll mail it to you, or go take a look at the archive or the RSS feed of the archives.

If you also wish to receive it every week by mail, you may subscribe online.

Alan Schmitt