OCaml: How to build mirage-tcpip using dune?

Question

I'm trying to build the examples at https://github.com/mirage/mirage-tcpip in the folder "examples".

First I did opam install. in the root directory to install all dependencies. Then I did dune build and it build everything in _build , lots of .a, .cma, .cmx, .cmi, .cmxa files that I don't know what are for ( can somebody explain ?).

Anyways, I think the examples have to be built separately, because they have their own dune files. But I tried running dune build on them and got:

root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# dune build
Entering directory '/workspaces/ocaml_env/mirage-tcpip'
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# ls
dune  ping.ml
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# cat dune 
(executables
 (names ping)
 (libraries cmdliner logs logs.fmt tcpip.icmpv4-socket))
root@66f08fd7c55b:/workspaces/ocaml_env/mirage-tcpip/examples/ping# dune build ping
Entering directory '/workspaces/ocaml_env/mirage-tcpip'
Error: Don't know how to build ping

Answer 1

Explanation of OCaml file types:

Regarding the file types in the _build directory ( reference 1 , reference 2 ):

• .a are standard archive files (also known as static libraries) containing native code:

  Arguments ending in.o or.a (.obj or.lib under Windows) are assumed to be C object files and libraries. They are passed to the C linker when linking in -custom mode (see the description of -custom below).

• .cma are the OCaml byte code equivalent of .a files, so static libraries, but with platform-independent OCaml byte code instead of machine-dependent native code:

  Arguments ending in.cma are taken to be libraries of object bytecode. A library of object bytecode packs in a single file a set of object bytecode files (.cmo files).

• .cmx contain meta-data for how to link native code object files together:

  Arguments ending in.ml are taken to be source files for compilation unit implementations. ... From the file x.ml, the ocamlopt compiler produces two files: xo, containing native object code, and x.cmx, containing extra information for linking and optimization of the clients of the unit.

• .cmi are compiled interface definition files:

  Arguments ending in.mli are taken to be source files for compilation unit interfaces. Interfaces specify the names exported by compilation units: they declare value names with their types, define public data types, declare abstract data types, and so on. From the file x.mli, the ocamlopt compiler produces a compiled interface in the file x.cmi.

• .cmxa are native code library files that combine .a / .o and and .cmx files, so like .a but with additional linking information from the .cmx files:

  Arguments ending in.cmxa are taken to be libraries of object code.

Building the example

Regarding the build of the ping example, to build an executable target with dune , you have to append .exe to the target name ( reference ):

Note that native code executables will have the.exe extension on all platforms (including non-Windows systems).

So the full sequence of build commands would be:

• Install dependencies:

   $ opam install.

• Build mirage-tcpip :

   $ dune build

• Build the ping example:

   $ cd example/ping $ dune build ping.exe

• Run the binary:

   # dune exec./ping.exe 8.8.8.8

  Alternatively, from the mirage-tcpip directory:

   #./_build/default/examples/ping/ping.exe 8.8.8.8