haskell - Flexibility of the hierarchy of module sources allowed in cabal project -

i have project source tree:

src/ src/a/ src/a/a.hs src/b/ src/b/c/ src/b/c/c.hs ... 

the 2 haskell files divide source code modules:

-- file a/a.hs module ... 

and

-- file b/c/c.hs module b.c ... 

the cabal file contains:

other-modules: a, b.c, ... hs-source-dirs: src/, src/a/, src/b/, src/b/c/, ... 

but while module a can found, cabal complains b.c:

cabal: can't find source b/c in ... 

i see no rational explanation why placing file defining module a under a/a.hs ok placing b.c under b/c/c.hs isn't. there workaround other placing c.hs directly under b (i maintain separation of sources)?

the reason error module b.c should defined in file b/c.hs, not b/c/c.hs (that module b.c.c). error have appeared if had 1 source dir 1 source file, not because of parts have put in.

also, dir appears in hs-source-dirs directive should root of dir tree, doubtful need of parts put in, instance, src/b/c (which treat src/b/c root.... meaning can define top level modules in dir. if doing that, consider mistake).

what want define multiple top level source dirs, this

a_src/a.hs b_src/b/c.hs  hs-source-dirs: a_src, b_src 

even better, suggest use stack, allows separate different modules own source dirs, called src, , independent .cabal files, allowing richer dependencies between each module.