$ opam install camlp4
The following actions will be performed:
 - install   camlp4.4.02.1+system
=== + 1 ===

=-=- Synchronizing package archives -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=  🐫

=-=- Installing packages =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=  🐫
Copying ~/.opam/repo/default/packages/camlp4/camlp4.4.02.1+system/files/install to ~/.opam/system/build/camlp4.4.02.1+system/
Copying ~/.opam/repo/default/packages/camlp4/camlp4.4.02.1+system/files/check-camlp4.sh to ~/.opam/system/build/camlp4.4.02.1+system/
Building camlp4.4.02.1+system:
  sh ./check-camlp4.sh
[ERROR] The compilation of camlp4.4.02.1+system failed.
Removing camlp4.4.02.1+system.
  Nothing to do.


#=== ERROR while installing camlp4.4.02.1+system ==============================#
# opam-version 1.2.0
# os           darwin
# command      sh ./check-camlp4.sh
# path         $home/.opam/system/build/camlp4.4.02.1+system
# compiler     system (4.02.1)
# exit-code    1
# env-file     $home/.opam/system/build/camlp4.4.02.1+system/camlp4-94259-58c514.env
# stdout-file   $home/.opam/system/build/camlp4.4.02.1+system/camlp4-94259-58c514.out
# stderr-file  $home/.opam/system/build/camlp4.4.02.1+system/camlp4-94259-58c514.err
### stdout ###
# ...[truncated]
# 4.02 by switching to a local installation via `opam switch 4.02.1`.
#
# Here are some installation instructions for camlp4 if you obtained OCaml
# via the OPAM binary packages:
#
# http://software.opensuse.org/download.html?project=home%3Aocaml&package=ocaml
#
# * Debian/Ubuntu: sudo apt-get install camlp4-extra
# * RHEL/CentOS/Fedora: sudo yum install ocaml-camlp4
#
### stderr ###
# ./check-camlp4.sh: line 3: camlp4orf: command not found

sudo port install ocaml-camlp4

opam switch 4.02.1
 eval `opam config env`