Comment author: administrator

Full_Name: Dr Andrew A. Adams
Version: Caml Light 0.75/0.75
OS: RedHat Linux 7.3
Submission from: viwc1.rdg.ac.uk (134.225.16.91)

I have an application I'm developing to teach first year students. It involves
implementing types for Binary, Octal and Hexadecimal numbers and defining
conversions between them, integers and string representations of the Binary,
Octal and Hex numbers. When I cam to write the final part of this I wanted to
translate a list of string representations between two number systems leading to
the expression:

(map string_of_Octal (map Octal_of_Binary (map Binary_of_string strs)))

which leads to an error:

File "translation.ml", line 16, characters 8-33:

			  (map Binary_of_string strs))));
			   ^^^^^^^^^^^^^^^^^^^^^^^^^

This expression has type Binary list,
but is used with type Binary list.

A gzipped tar file with all the code is available at:

http://www.personal.rdg.ac.uk/~sis00aaa/BODH.tgz

include "translation";;

will show the error.

Your problem is due to multiple redefinitions of types, since some
files that define basic types of the application are loaded more than
once (hence redefining over and over again the types they already
defined). This problem is explained in long in the FAQ of the
language: it is the first question about typing

* Error message: a type is not compatible with itself ?

Have a look to http://pauillac.inria.fr/caml/FAQ/FAQ_EXPERT-eng.html

The solution is to clear all the include directives into your files
(except for the last one). Somewhat better, you should add a new
main.ml file to contain the set of include directives necessary to
build your application:

(* File main.ml *)
include "binary";;
include "octal";;
include "hex";;
include "chunk";;
include "translate";;
include "transdec";;
include "dectrans";;
include "reading";;
include "writing";;
include "translation";;

(* End of file main.ml *)

This completely clarifies the situation :)

Then a new type error is reported:

File "translation.ml", line 11, characters 17-34:

                                  (map Decimal_of_Binary
                                       ^^^^^^^^^^^^^^^^^

The value identifier Decimal_of_Binary is unbound.

in effect:

$ grep Decimal_of_Binary *.ml
translation.ml: (map Decimal_of_Binary

But this one is yours ...

Even better, you could use modules that would be compiled separately and
build your entire system using a Makefile (the FAQ gives examples of
Makefile where you just have to list the files to get your application
automatically built). This is easy and scalable ...

Hope this helps.

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://pauillac.inria.fr/~weis/

Comment author: administrator

FAQ (type redefinition).