The problem is that executable `ppx_forest` and library `forest_ppx` both refer to the same compilation unit `ppx_forest`. So the solution is easy, just remove the `Ppx_forest` module from the library (indeed, it is not part of the library, it is the executable implementation). Here is the PR with the fix: https://github.com/padsproj/oforest/pull/9. # Details Just in case if you're interested why the resulting error was so confusing :) The error message came from the following compilation command: ocamlfind ocamlopt -linkpkg -g -linkpkg -thread -package threads -package str -package re.str -package re.glob -package re -package ppx_tools.metaquot -package ppx_let -package ppx_deriving.show -package pads.ppx -package pads -package core -package compiler-libs.common ppx/forest_ppx.cmxa parsing/forest_parser.cmxa lib/forest.cmxa ppx/ppx_forest.cmx -o ppx/ppx_forest.native It is obvious that the command is incorrect (pun intended). Let's, actually, remove all the packages so that we can see the libraries: ocamlfind ocamlopt -linkpkg ppx/forest_ppx.cmxa parsing/forest_parser.cmxa lib/forest.cmxa ppx/ppx_forest.cmx -o ppx/ppx_forest.native In fact, the problem is in library ordering. Modules and libraries must be sorted in topological order, so the first should be `lib/forest.cmxa`, then `parsing/forest_parser.cmxa` and finally `forest_ppx.cmxa`. And, yes, this is how this command looks after the fix: ocamlfind ocamlopt -linkpkg lib/forest.cmxa parsing/forest_parser.cmxa ppx/forest_ppx.cmxa ppx/ppx_forest.cmx -o ppx/ppx_forest.native So how the toposort can be broken? My assumption, that this was because you introduced a loop into a dependency graph, when you added ppx_forest to both: the library and the executable. If my assumption is true, then probably we should add to ocamlbuild toposort routine an easy check that will detect loops and output a proper diagnostic message if a dependency graph contains cycles. Regards, Ivan Gotovchits On Fri, Oct 28, 2016 at 2:14 AM, Jonathan DiLorenzo < dilorenzo@cs.cornell.edu> wrote: > Hmm, sadly this seems to still produce the same error after cleaning up > all the oasis generated files and everything: > > File "_none_", line 1: > Error: No implementations provided for the following modules: > Forest_parser_helper referenced from ppx/forest_ppx.cmxa(Skins) > Command exited with code 2. > > Maybe notable (or maybe obvious) that if I switch oasis to use ocamlc > instead of ocamlopt, I instead get: > > File "_none_", line 1: > Error: Error while linking ppx/forest_ppx.cma(Skins): > Reference to undefined global `Forest_parser_helper' > Command exited with code 2. > > New _oasis file (not with best -> byte change): > > Library forest_parser > Path: parsing > BuildTools: ocamlbuild, menhir, ocamllex > Findlibparent: forest > Findlibname: forest_parser > BuildDepends: forest, ppx_deriving.show, compiler-libs.common > CompiledObject: best > Modules: Forest_parser_helper, Forest_types > InternalModules: Forest_lexer, Forest_parser > > Library forest_ppx > Path: ppx > BuildTools: ocamlbuild > Findlibparent: forest > Findlibname: forest_ppx > BuildDepends: re, re.str, forest.forest_parser, forest, > ppx_tools.metaquot > CompiledObject: best > Modules: Ppx_forest > InternalModules: Ppx_forest_lib, Utility, Skins > XMETAEnable: true > XMETADescription: Syntax extension library for OCaml Forest > XMETARequires: str re core threads ppx_tools.metaquot > XMETAExtraLines: ppx = "ppx_forest" > > Executable ppx_forest > Path: ppx > MainIs: ppx_forest.ml > BuildDepends: forest, forest.forest_parser, forest.forest_ppx, > pads.ppx, ppx_tools.metaquot > CompiledObject: best > > > On Thu, Oct 27, 2016 at 2:24 PM, Ivan Gotovchits wrote: > >> The problem is in a name clashing between `$opam-switch/lib/ocaml/compiler-libs/parser` >> and the `parser` library that is compiled from your internal library named >> `parser.cmxa`. >> The compiler-lib is added to the search path by the `ppx_tools` library, >> and when you're trying to link your final executable, it takes the wrong >> archive, that definitely doesn't have >> `Forest_parser_helper` module. >> >> The reason, why it is still able to see that there is no `bad_func` in >> `Forest_parser_helper` is because the interfaces are not contained in the >> `cmxa` file, but are looked up directly in >> the `cmi`. Compiler is looking for a file named >> `forest_parser_helper.cmi` and can see that there are not `bad_func` there. >> >> The solution is to rename your library, e.g., use `Library forest_parser` >> instead of `Library parser` >> >> On Thu, Oct 27, 2016 at 1:44 PM, Jonathan DiLorenzo < >> dilorenzo@cs.cornell.edu> wrote: >> >>> Hey, >>> >>> Ok, now the next step would be the following. Carefully check that all >>>> modules, that you're using in libraries are included in `Modules` or >>>> `InternalModules`. It is the case >>>> that sometimes when you forgot to include a module, oasis (actually >>>> `ocamlbuild`), may produce a strange, and on a first glance, irrelevant >>>> error message. >>>> >>> >>> I checked and sadly the modules I'm trying to access are all in >>> `Modules`. Perhaps interestingly, it can still clearly detect statically if >>> the function exists or not because if I try to use a function that doesn't >>> exist it instead gives me this error (which is what I would normally >>> expect): >>> >>> File "ppx/skins.ml", line 39, characters 8-37: >>> Error: Unbound value Forest_parser_helper.bad_func >>> Command exited with code 2. >>> >>> >>>> If it doesn't help then the `_build/_log` file might help us to debug >>>> the issue. >>>> >>> >>> Attached. Thanks so much for helping with this again. I'm at a total >>> loss. >>> >>> >>>> >>>> On Thu, Oct 27, 2016 at 10:59 AM, Jonathan DiLorenzo < >>>> dilorenzo@cs.cornell.edu> wrote: >>>> >>>>> Hey Ivan, >>>>> >>>>> Thanks for your response. >>>>> >>>>> The first one is that you didn't run `oasis setup` after you made the >>>>>> changes, so I would suggest cleaning current state >>>>>> and starting from scratch. (I usually just do `git clean -idx` just >>>>>> to be sure that I got rid of any generated files, like setup.data, et alas, >>>>>> but be careful, >>>>>> don't delete something that you need). >>>>>> >>>>> >>>>> I tried cleaning up all the generated files. Same error unfortunately >>>>> >>>>> >>>>>> Another idea is that you're using oasis 0.4.7 with >>>>>> ocaml-4.03.0+flambda, they are currently incompatible, and can produce >>>>>> weird bugs. If that so, then consider switching >>>>>> either a compiler or oasis to different versions. >>>>>> >>>>> >>>>> I am using oasis 0.4.7 and ocaml-4.03.0, but I don't appear to be >>>>> using flambda. I tried passing in -config and it said that flambda was >>>>> false at least, but I admit, I'm not especially familiar with it, so if >>>>> there's some other way I should be checking for this please let me know. >>>>> Hopefully, they're compatible sans flambda? >>>>> >>>>> >>>>> On Thu, Oct 27, 2016 at 1:01 AM, Jonathan DiLorenzo < >>>>>> dilorenzo@cs.cornell.edu> wrote: >>>>>> >>>>>>> Hey all, >>>>>>> >>>>>>> I'm trying to build my system using Oasis and OCamlbuild. I have 3 >>>>>>> different libraries and for some reason I seem to only be able to refer >>>>>>> from one to the other in seemingly random files. For example, I want my >>>>>>> 'ppx' library to be able to use functions from my 'parser' library. One >>>>>>> file (ppx_forest.ml) can use functions from it, while another in >>>>>>> the same library (skins.ml) cannot, giving me this error: >>>>>>> >>>>>>> File "_none_", line 1: >>>>>>> Error: No implementations provided for the following modules: >>>>>>> Forest_parser_helper referenced from ppx/ppx.cmxa(Skins) >>>>>>> Command exited with code 2. >>>>>>> >>>>>>> They can all refer to types I've defined therein though. >>>>>>> >>>>>>> I'm not fantastic at Oasis so maybe I'm just missing something >>>>>>> basic? Any ideas? Any more information I can gather to give more context >>>>>>> otherwise? >>>>>>> >>>>>>> Thanks in advance, >>>>>>> Jonathan >>>>>>> >>>>>>> Excerpt of my Oasis file that may possibly be relevant: >>>>>>> >>>>>>> Library forest >>>>>>> Path: lib >>>>>>> BuildTools: ocamlbuild >>>>>>> BuildDepends: pads, str, re, re.glob, core, threads, ppx_let >>>>>>> CompiledObject: best >>>>>>> Modules: Forest, PadsInterface >>>>>>> >>>>>>> Library parser >>>>>>> Path: parsing >>>>>>> BuildTools: ocamlbuild, menhir, ocamllex >>>>>>> Findlibparent: forest >>>>>>> Findlibname: parser >>>>>>> BuildDepends: forest, ppx_deriving.show, compiler-libs.common >>>>>>> CompiledObject: best >>>>>>> Modules: Forest_parser_helper >>>>>>> InternalModules: Forest_lexer, Forest_parser, Forest_types >>>>>>> >>>>>>> Library ppx >>>>>>> Path: ppx >>>>>>> BuildTools: ocamlbuild >>>>>>> Findlibparent: forest >>>>>>> Findlibname: ppx >>>>>>> BuildDepends: re, re.str, forest.parser, forest, >>>>>>> ppx_tools.metaquot >>>>>>> CompiledObject: best >>>>>>> Modules: Ppx_forest >>>>>>> InternalModules: Ppx_forest_lib, Utility, Skins >>>>>>> XMETAEnable: true >>>>>>> XMETARequires: str re core threads ppx_tools.metaquot >>>>>>> XMETAExtraLines: ppx = "ppx_forest" >>>>>>> >>>>>>> Executable ppx_forest >>>>>>> Path: ppx >>>>>>> MainIs: ppx_forest.ml >>>>>>> BuildDepends: forest, forest.parser, forest.ppx, pads.ppx, >>>>>>> ppx_tools.metaquot >>>>>>> CompiledObject: best >>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>> >> >