Compiling

aclocal && autoconf && automake && ./configure
make

That first line should be run whenever Makefile.am is edited.

Using MPFR

First, install MPFR: brew install mpfr

Then, install the Ocaml bindings to it: opam install mlgmpidl

In src/marshall.ml, change the code to

module Marshall_bignum = Main.Make(Dyadic_mpfr)

In Makefile.am, add -pkgs gmp to MARSHALLOCAMLBUILD. Whenever you edit Makefile.am, the next step is then to run

aclocal && autoconf && automake && ./configure

before running make.