OCaml Getting started with OCaml Installation on Windows (native)

Example

Premise

These instruction shows a procedure to install native OCaml binaries in Windows. If your operative system is Windows 10 (Insider Preview) build 14316 or later you can also install OCaml through Bash on Ubuntu on Windows. In this case, follow the instruction to install OCaml on Ubuntu.

Install OCaml and Opam

Download OCaml official distribution. It contains both OCaml compilers and Opam packet manager. Suppose you have installed the software in C:/OCaml. To be sure you've correcly installed OCaml open cmd.exe and type ocaml.

If you see the message 'ocaml' is not recognized as an internal or external command, operable program or batch file you need to add C:/OCaml/bin to your Path (Environment Variable).

Add OCaml binaries to path

in Control Panel > System and Security > System > Advanced system settings (on the left) > Environment Variables and then select Path in System Variable tab, then Edit.

Add C:/OCaml/bin; to the list.

Install Cygwin

Without Cygwin you can't use Opam. In fact, if you try to open Opam typing opam in cmd.exe it shows a message: Fatal error: exception Unix.Unix_error(20, "create_process", "cygcheck").

Download Cygwin and start the installer. Be sure to check the following packages:

• automake
• diffutils
• libreadline
• make
• m4
• mingw64-x86_64-gcc-core
• mingw64-x86_64-gmp
• mingw64-x86_64-openssl
• mingw64-x86_64-pkg-config
• mingw64-x86_64-sqlite3
• patch
• rlwrap
• unzip
• wget

Suppose you have installed the software in C:/cygwin (C:/cygwin64 for 64bit version). Open cmd and type wget (or one of the executable present in C:/cygwin/bin) to check if you can use the Cygwin executables. If the executable won't open, add C:/cygwin/bin to your Path (Environment Variable).

Configure Opam

Open cmd.exe and type opam init to configure Opam.

Then install ocamlfind (part of the OCaml compiler) with

opam install ocamlfind
opam config env

Check if ocamlfind is installed typing it in cmd.exe.

The command opam config env is used to add opam's executables directory to the enviroment path. If after logout you cannot reach ocamlfind anymore, you can manually add it adding to path the following line: C:/Users/<your user>/Documents/.opam/system/bin/.

Installing packages

Packages are installed through Opam with the command opam install xyz where xyz is the name of the package.

Install UTop

Try running the command opam install utop. If you have no errors, then typing utop will open the executable.

If you see the message

[ERROR] The compilation of zed failed at "ocaml setup.ml -build".

you have to manually install the single packages. Try again typing:

opam install zed
opam install lambda-term
opam install utop

Both lambda-term and utop might not install. See Troubleshoot section.

Installing Core

You can install core package with opam install core. On Windows 64bit version (and 64bit Cygwin) you will see the following error:

[ERROR] core is not available because your system doesn't comply with os != "win32" & ocaml-version = "4.02.3".

Troubleshoot: cannot create regular file

If package with name xyz.10.1 fails to install (where xyz is the name of the package, and 10.1 its version) with the following message:

install: cannot create regular file '/cygdrive/c/Users/<your user>/Documents/.opam/system/bin/<something>': File exists

You have to go in this directory:

C:\Users\<your user>\Documents\.opam\repo\default\packages\<xyz>\<xyz.10.1>\files 

and delete the file xyz.10.1.install.

Troubleshoot: cannot load shared library

If you try to open some Opam's package (eg: utop) and you see this error:

Fatal error: cannot load shared library dlllwt-unix_stubs
Reason: The specified module could not be found.

Run opam config env again and try to reopen the executable.