Can't open Llvm in ocaml - functional-programming

Question

I'm trying to use llvm binding in ocaml, in my file test.ml, I have one line of code:
open Llvm
When I run the command
ocamlbuild -use-ocamlfind test.byte -package llvm
I get this result:
+ ocamlfind ocamldep -package llvm -modules test.ml > test.ml.depends
ocamlfind: Package `llvm' not found
Command exited with code 2.
Compilation unsuccessful after building 1 target (0 cached) in 00:00:00.
What did I do wrong in this? Thanks.
BTW, the _tag file contains:
"src": traverse
<src/{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
myocamlbuild.ml contains:
open Ocamlbuild_plugin;;
ocaml_lib ~extern:true "llvm";;
ocaml_lib ~extern:true "llvm_analysis";;
flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;

Answer 1

I don't know why the instructions that you're using are so complex. You don't have to do anything like this to use llvm bindings in OCaml, provided you have installed them via opam.
Here is the recipe:
Install llvm bindings via opam.
it could be as simple as
opam install llvm
However, opam may try to install the latest version that is not available on your system, so pick a particular version, that you have and do the following (suppose you have llvm-3.8):
opam install conf-llvm.3.8
opam install llvm --criteria=-changed
(The -criteria flag will prevent opam from upgrading conf-llvm to the newest version)
Once it succeeds, you can easily compile your programs without any additional scaffolding.
Create and build your project
create a fresh new folder, e.g.,
mkdir llvm-project
cd llvm-project
create a sample application (borrowed from some tutorial, that I've found online):
cat >test.ml<<EOF
open Llvm
let _ =
let llctx = Llvm.global_context () in
let llmem = Llvm.MemoryBuffer.of_file Sys.argv.(1) in
let llm = Llvm_bitreader.parse_bitcode llctx llmem in
Llvm.dump_module llm ;
()
EOF
compile it for bytecode
ocamlbuild -pkgs llvm,llvm.bitreader test.byte
or to the native code
ocamlbuild -pkgs llvm,llvm.bitreader test.native
run it
./test.native mycode.bc