Gobi

A boilerplate based on JBuilder and opam-cross-ios for creating static iOS libraries with OCaml and Reason.

The name comes from the Gobi Desert, which is the only desert with wild camels (Thank you to wokalski to let me take over this awesome name :))

Getting started

Requirements:

• You must have OPAM installed.
• You must have the Xcode command line tools installed (e.g. with xcode-select --install)

1. Clone this repo.
2. There is a script gobi.sh in the root of this project. Checkout the variables at the top of the script and see if you have to adapt them for your needs.
3. Source the bash script gobi.sh (e.g. with source gobi.sh)
4. Run gobi_setup. This will create a set of different switches, install the necessary compilers and dependencies.
5. Install some packages with gobi_install. For the example project we need to instal re. This can be done with gobi_install re-ios.
6. Create the static library with gobi_create_library
7. Open the CrossIOSTest project and run it :)

Note: The install for reason seems to fail undeterministically. If it happens just try again with gobi_install reason.

Details

Okay here a lot of things going on and I try to explain the different parts. Generally, any native iOS library would have to be compiled four times: for 64-bit (and 32-bit) device and simulator. OPAM offers no help here; due to the way OPAM packages currently work, the only realistic option is to create four switches, one switch per target, and build everything four times

JBuilder

JBuilder is a build system for OCaml and Reason for details take look into the excellent [documentation]((http://jbuilder.readthedocs.io/en/latest/). But that is not the complete truth. Currently JBuilder doesn't support creating object files nor cross-compilation. I implemented these features in a fork of mine and installed this version previously. I try to upstream my changes, but they are also on the Roadmap for 1.1 so soon we get a stable version! In order to configure everything there are two ne stanzas available. A jbuild-workspace context now additionally has an optional host field which enables toolchains like iOS. And the executable now has additionally a targets stanza which takes (<targets>) where <targets is a subset from object and executable. If object is set now additionally you can build myFile.exe.o for on object-file (with the -output-obj flag).

gobi.sh

gobi.sh is actually just a bunch of helper scripts which took inspiration from opam-cross-ios. The following functions are available:

• gobi_working_switch sets opam to the defined working switch (by default 64-bit simulator)
• gobi_create_switches creates all necessary switches
• gobi_foreach <your_command> iterates over all switches and executes each command once per switch
• gobi_install <packages> is just an alias for gobi_foreach opam install <packages>.
• gobi_remove <packages> is just an alias for gobi_foreach opam remove <packages>.
• gobi_create_library will create a fat static library (with lipo), i.e. all architectures in one.

Packages

The best would be to just read the description from whitequark. Here is a list of already ported packages. re-ios is one example of these.

Bindings / C-Interop

In order to call OCaml from Objective-C we have to do two things:

1. Register callbacks, this is done in hello_world.re
2. Write some thin C-wrappers. You can find examples in bindings. The best guide for the c-bindings is probably the official manual. A good way to start would propbably be to look at the examples in this repo and then search the functions in the manual to understand what happens. Note: The better way would actually to use ctypes to generate the functions, but I wasn't able to get that compiled for iOS ... Any help would be appreciated!

JBuild configuration

The jbuild file in src has the following rule

(rule
 ((targets (libgobi.a))
  (deps    (hello_world.exe.o ../bindings/bindings.o))
  (action  (bash "\
    cp ${ocaml_where}/libasmrun.a libgobi.a && chmod +w libgobi.a;\
    ar r libgobi.a hello_world.exe.o ../bindings/bindings.o;\
    "))))

This rule combines our OCaml code hello_world.exe.o and our bindings ../bindings/bindings.o together with the ocaml (libasmrun.a) runtime to a static archive.

Acknowledgements

Opam-cross-ios is based on the work by whitequark. The OCaml cross-compiler in opam-cross-ios is based on a patchset by Gerd Stolpmann.

JBuilder is built by the fine folks at Jane Street