Measures

Measures

[Jon Harrop]

This latest post about statically typing constraints beyond mere 
floating-point values reminds me that the F# programming language just got 
another new feature called "measures" that lets you add phantom types 
representing units of measure and even handles arithmetic over them for you.

I have not used measures yet myself but I was just wondering if the OCaml 
world had already seen anything like this?

I had been under the impression that this could not be made to work but, 
obviously, I was wrong!

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e

Re: [Caml-list] Measures

[Hezekiah M. Carty]

On Sun, Sep 21, 2008 at 7:30 PM, Jon Harrop
<jonathandeanharrop@googlemail.com> wrote:
>
> This latest post about statically typing constraints beyond mere
> floating-point values reminds me that the F# programming language just got
> another new feature called "measures" that lets you add phantom types
> representing units of measure and even handles arithmetic over them for you.
>
> I have not used measures yet myself but I was just wondering if the OCaml
> world had already seen anything like this?
>
> I had been under the impression that this could not be made to work but,
> obviously, I was wrong!

Jon,

The OSP Delimited Overloading project has an example which does a very
simple version of something similar to F# measures.  The relevant
example files can be viewed here:

https://forge.ocamlcore.org/plugins/scmsvn/viewcvs.php/trunk/examples/length/?root=pa-do

The underlying Length library code is based on a post by Richard
Jones' (http://camltastic.blogspot.com/2008/05/phantom-types.html) and
the syntactic sugar comes from the work done by the Delimited
Overloading folks.  It does not provide the very cool "x meters per
second times y seconds gives z meters" that the F# feature seems to
provide, but it does provide a start - meters + feet will throw a
compile-time error, for example.

Hez

-- 
Hezekiah M. Carty
Graduate Research Assistant
University of Maryland
Department of Atmospheric and Oceanic Science