I'm trying to do a basic stack project named http-lesson (Chapter 39 from *Get Programming with Haskell) *which starts out with this in Main.hs module Main where import qualified Data.ByteString as B import qualified Data.ByteString.Char8 as BC import qualified Data.ByteString.Lazy as L import qualified Data.ByteString.Lazy.Char8 as LC import Network.HTTP.Simple After doing stack new http-lesson, the books says to modify the http-lesson.cabal file in the project, adding bytestring and http-conduit for the imports noted above executable http-lesson-exe main-is: Main.hs other-modules: Paths_http_lesson hs-source-dirs: app ghc-options: -threaded -rtsopts -with-rtsopts=-N build-depends: base >=4.7 && <5 , http-lesson , bytestring , http-conduit default-language: Haskell2010 Being a beginner, I follow the cookbook-like directions, i.e., I next run stack build . . . and it errors out, not finding the imported stuff. But then when I check the http-lesson.cabal file, the extra packages I added have been removed. Hunting around, I find this https://schooloffp.co/2020/12/05/whirlwind-tour-of-stack-for-beginners.html that tells me to put the extra packages in package.yaml. Very confused at this point. ⨽ Lawrence Bottorff Grand Marais, MN, USA borgauf@gmail.com