Re: [Caml-list] Ocaml, Objective-c, and XCode
John Whitington
On 11/02/2010 01:28, Andrew Webb wrote:
> Hi there,
>
> I have a few questions relating to using Ocaml with objective-c for anyone who programs on a Mac. I am aware that there aren't any real bindings between ocaml and objective-c/cocoa, so I am investigating rolling my own. So:
>
> 1) Does anyone have experience in interfacing ocaml and objc? Is it difficult?
> 2) Does anyone have a small example project that does mix these two languages? I have looked at unison, but it is too big for me to get my head around. I am thinking more on the scale of the ubiquitous Currency Converter...
> 3) Does anyone who is mixing these languages use Xcode to do so? If so, what steps do you need to go through to set that up?
>
> A big thanks to anyone who can answer (some of) these questions. I am trying to decide whether to use haskell or ocaml for my next cocoa application, as these are the two languages I am most comfortable. I have recently found an excellent description of how to do this using haskell (http://tscheff.blogspot.com/2010/02/currync-converter-using-haskell-with.html) and was wondering if there were such resources for ocaml.
I've just released a product written in this way:
http://www.coherentpdf.com/proview.html
I just have a normal makefile which builds a .a library from the ocaml
code and its C wrapper as per the instructions in the ocaml manual.
The xcode project then uses the .a and the .h of the wrapper and a few
extra compilation and linking flags. Doubtless with a little bit more
effort, Xcode could be made to call the ocaml makefile.
Here's the OCaml makefile:
mklib:
ocamlc cpdf.mli;
ocamlopt -c -I . unix.cmxa str.cmxa bigarray.cmxa cgutil.cmxa
camlpdf.cmxa cpdf.ml;
ocamlc cpdflib.mli;
ocamlopt -c -I . unix.cmxa str.cmxa bigarray.cmxa cgutil.cmxa
camlpdf.cmxa cpdf.cmx cpdflib.ml;
ocamlc cpdflibc.mli;
ocamlopt -c -I . unix.cmxa str.cmxa bigarray.cmxa cgutil.cmxa
camlpdf.cmxa cpdf.cmx cpdflib.cmx cpdflibc.ml;
ocamlc cpdflibwrapper.c;
ocamlopt -output-obj -o cpdflibc.o unix.cmxa str.cmxa
bigarray.cmxa cgutil.cmxa camlpdf.cmxa cpdf.cmx cpdflib.cmx cpdflibc.cmx;
cp /usr/local/lib/ocaml/libasmrun.a cpdflib.a;
ar r cpdflib.a cpdflibc.o cpdflibwrapper.o
test: zlibstubs.o cpdflib.a
cc -m32 -c cpdflibc-test.c -o cpdflibc-test.o; \
cc -m32 -L'/usr/local/lib/ocaml' -lunix -lbigarray -lstr -lz -o
test cpdflibc-test.o zlibstubs.o cpdflib.a
(The 'test' target shows you the kind of compiler and linker flags you'd
need to put into XCode).
Basically, once you've got the usual ocaml/c interface done, the Xcode
part is no problem.
Cheers,
--
John Whitington
Director, Coherent Graphics Ltd
http://www.coherentpdf.com/
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Andrew
Thanks for the information!
>
> I've just released a product written in this way:
>
> http://www.coherentpdf.com/proview.html
>
Indeed, and I posted a similar question on your blog at about the same
time as I posted this question. :-)
> I just have a normal makefile which builds a .a library from the ocaml
> code and its C wrapper as per the instructions in the ocaml manual.
>
> The xcode project then uses the .a and the .h of the wrapper and a few
> extra compilation and linking flags. Doubtless with a little bit more
> effort, Xcode could be made to call the ocaml makefile.
>
> Basically, once you've got the usual ocaml/c interface done, the Xcode
> part is no problem.
>
Thank you, that is all excellent information!
Ta,
Andrew
dynas...@mac.com
> I have a few questions relating to using Ocaml with objective-c for
> anyone who programs on a Mac.
We've been working with OCaml/ObjC/Cocoa on the iPhone for a while. We
also have a small subset working on the Mac and have built Mac apps with
it.
> I am aware that there aren't any real bindings between ocaml and
> objective-c/cocoa, so I am investigating rolling my own.
This is what we did. There was some work on an OCaml/Cocoa bridge, but
it doesn't appear to be finished, and doesn't look like an active
project. The home page is here:
http://code.google.com/p/objective-c-caml-bridge
> 1) Does anyone have experience in interfacing ocaml and objc? Is it
> difficult?
The things that make it easier than it could be are:
(a) There is good documentation on interfacing OCaml and C, and ObjC is
a clean superset of C. So the language tools all work together
quite well.
(b) The OO subsystem of OCaml is a pretty good match for the Cocoa
design. With some work, you can use OCaml objects to represent
Cocoa objects, and vice versa.
The hard parts are:
(a) Cocoa is a very large system, too large for a small number of people
to build an interface by hand. A mechanical interface generator
would be best, but is also a big project.
(b) There's a mismatch between the ObjC reference counting and OCaml GC.
For our work, we just add bits to our interface as we need them. Memory
management issues are tricky but only need to be solved once in the
lowest layer. We don't have any experience with the ObjC GC; this might
make things a little trickier.
One thing to note is that we like OCaml because it's very flexible and
expressive. If you mechanically translate all Cocoa objects and structs
into their obvious OCaml corollaries, you lose a lot of the advantage of
using OCaml. For example, we map Cocoa NSPoint values into OCaml
2-tuples, not into OCaml records. And we often use OCaml lists (with
the correct base type) to represent NSArray objects. Because of this,
we don't think a direct mechanical translation of Cocoa into OCaml is
going to work. But a mechanical translation with sufficient overrides
probably would.
> 2) Does anyone have a small example project that does mix these two
> languages? I have looked at unison, but it is too big for me to get my
> head around. I am thinking more on the scale of the ubiquitous
> Currency Converter...
I don't know of anything.
> 3) Does anyone who is mixing these languages use Xcode to do so? If
> so, what steps do you need to go through to set that up?
To be honest, we don't currently use Xcode in any non-trivial way. We
just use its built-in knowledge about packaging up applications. There
was a project to integrate OCaml into Xcode, but again it doesn't look
like an active project. The home page is here:
http://maxao.free.fr/xcode-ocaml-plugin
Jeff Scofield
Seattle