stack install elm-export fails - elm

Question

I would like to install elm-export package using stack. It needs to be imported in a servant-elm example.
It's like:
shell> stack install elm-export
shell>
No error message. So I thought it's installed.
But when I stack build,
Error message shows:
test-0.1.0.0: build (exe)
Preprocessing executable 'test' for test-0.1.0.0..
Building executable 'test' for test-0.1.0.0..
[1 of 1] Compiling Main ( src\Main.hs, .stack-
work\dist\5c8418a7\build\test\test-tmp\Main.o )
C:\Code\Haskell\11_Stack-Projects-That-Need-Dependency\test\src\Main.hs:6:1:
error:
Could not find module ▒▒Elm▒▒
Use -v to see a list of the files searched for.
|
6 | import Elm (Spec (Spec), specsToDir, toElmDecoderSource,
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
My question is, Where can I check if the package is installed? And how do I fix this?
ps. Cabal successfully installed elm-export and servant-export and runghc successfully run example code. Now I am trying to use stack to install package to prevent from ruining some dependency.

Answer 1

If you want to use this library in a haskell stack package you don't need to run stack install. Instead you need to add it to your project dependencies.
See the HaskellStack User Guide (adding dependencies)
Depending on the version of stack you have this might be in one of two places I think:
if you have a packages.yaml, add it in the section 'dependencies'
dependencies:
- base >= 4.7 && < 5
- elm-export >= 0.6 && < 1.0
if you don't have packages.yaml, add it to you cabal file directly
library
hs-source-dirs:
src
build-depends:
base >=4.7 && <5
, elm-export >= 0.6 && < 1.0
FYI: stack install is used to install executables which you can then use on the command line. It can be used inside or outside of haskell stack projects.
I don't think elm-export declares any executables, which is why it didn't output anything. Some examples are pandoc, hindent, etc. These are haskell libraries which also provides executables that you can install using stack.
$ stack install pandoc
...
Copied executables to /Users/<me>/.local/bin:
- pandoc
$ pandoc --help
pandoc [OPTIONS] [FILES]
-f FORMAT, -r FORMAT --from=FORMAT, --read=FORMAT