CODEWITHSUNDEEP
haskellhaskell-stack
Mark Karavan
Mark Karavan

Reputation: 2674

Importing sub-packages with stack

I don't understand how to import "sub-packages" in stack (if this is not the correct term, please let me know so I can edit).

Here's the top of a simple file: 

{-# LANGUAGE OverloadedStrings #-}

module Conduit where

import Data.Conduit
import qualified Data.Conduit.List as CL
import qualified Data.Conduit.Binary as CB

Two dependencies are listed. In myproject.cabal, I have:

executable myproject
  hs-source-dirs:      src
  main-is:             Main.hs
  default-language:    Haskell2010
  build-depends:       base >= 4.7 && < 5,
                       conduit

stack build -v gives me this error:

2018-02-08 13:28:06.923836: [warn] 7 | import qualified Data.Conduit.Binary as CB

I am not sure what to include in the cabal executable directive, each of these throws errors:

  build-depends:       base >= 4.7 && < 5,
                       conduit,
                       conduit.list,
                       conduit.binary

  build-depends:       base >= 4.7 && < 5,
                       conduit,
                       conduit-list
                       conduit-binary

Upvotes: 0

Views: 212

Answers (1)

duplode
duplode

Reputation: 34378

Data.Conduit.Binary is a module. It is part of a package called conduit-extra. Packages are what Stack (and cabal-install, were you using that instead) installs, and what you should add to the build-depends of the .cabal file:

  build-depends:       base >= 4.7 && < 5,
                       conduit,
                       conduit-extra

As for Data.Conduit.List, it is part of the conduit package, so you don't need another entry for it. One quick way of clarifying such things is doing a Hoogle search for the module (the package it belongs to will be pointed out in the top bar of the documentation page).

See also: What's the difference between module, package and library in Haskell?; Packages, modules and import in Haskell.

Upvotes: 3

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