making OPAM work with system compiler under MacOS X

Question

I am trying to do a very basic installation of OPAM under MacOS. Using macports I've installed following packages:

1. opam @1.2.0
2. ocaml-findlib @1.5.5
3. ocaml-camlp4 @4.02.0.1_1

when I did opam init (not as root, since I only need it for one user). opam switch shows me that I am using system compiler:

system C system System compiler (4.02.1)

Then I tried to install 'lwt' via opam it failed halfway with errors:

# ocamlfind: Package `camlp4' not found
# W: Failure("Command ''/Users/lord/.opam/system/bin/ocamlfind' query -format %d camlp4 > '/var/folders/hh/h6kt24208xj44z0059_xd9rh0000gn/T/oasis-ca8248.txt'' terminated with error code 2")

This is my opam list:

# Installed packages for system:
base-bigarray           base  Bigarray library distributed with the OCaml compil
base-threads            base  Threads library distributed with the OCaml compile
base-unix               base  Unix library distributed with the OCaml compiler
camlp4         4.02.1+system  Camlp4 is a system for writing extensible parsers
ocamlfind              1.5.5  A library manager for OCaml

I have noticed that it has it own ocamlfind, not system one. Perhaps this is what is causing error:

$ /Users/lord/.opam/system/bin/ocamlfind query -format %d camlp4
ocamlfind: Package `camlp4' not found

$ /opt/local/bin/ocamlfind query -format %d camlp4
/opt/local/lib/ocaml/camlp4

I tried before installing OCAML compiler and CAMLP via OPAM and it this case it works, but it bothers me that I have two compiler installations for the same version. I would rather use system OCAML compiler and CAMLP, if possible.

Answer 1

I'm not sure what goes wrong on your installation, maybe you shouldn't install ocaml-findlib as they may conflict in some manner. I will look at this later. Currently, the following works

$ sudo port install ocaml ocaml-camlp4 opam
$ opam init
$ opam install ocamlfind

This will lead to a working installation:

$ ocamlfind query camlp4
/opt/local/lib/ocaml/camlp4
$ which ocamlfind
/Users/ivg/.opam/system/bin/ocamlfind

Update

I've checked my hypothesis that system's ocamlfind may conflict with the opam's one. It doesn't get any evidence. Even if you install both of them everything works fine:

$ sudo port install ocaml-findlib
$ opam init

System's ocamlfind works pretty well:

$ ocamlfind query camlp4
/opt/local/lib/ocaml/camlp4
$ which ocamlfind
/opt/local/bin/ocamlfind

Now let's try to install it from opam:

$ opam install ocamlfind

It also works pretty well:

$ ocamlfind query camlp4
/opt/local/lib/ocaml/camlp4
$ which ocamlfind
/Users/ivg/.opam/system/bin/ocamlfind

And

$ opam install lwt

worked pretty fine too.

So, maybe you moved somewhere in a wrong direction, and you can just remove your ~/.opam and start from scratch. And also, I hope that you didn't forget to activate your opam with magical:

$ eval `opam config env`

command.