gistfile1.hs

streamFiles ::  IO () -> [FilePath] -> Source IO (Flush Builder)
streamFiles ready filepaths  = do
  --liftIO $ ready
  yield $ Chunk $ fromLazyByteString "{"
  mapM_ (\x -> do
            DCC.sourceFile x $= transducer
            yield $ Chunk $ fromLazyByteString ",\n")
    filepaths
  yield $ Chunk $ fromLazyByteString "}"

transducer :: ConduitM Text (Flush Builder) m1 a0
transducer = undefined

gistfile2.txt

src/Net/Tribe.hs:264:13:
    No instance for (MonadResource IO)
      arising from a use of ‘DCC.sourceFile’
    In the first argument of ‘($=)’, namely ‘DCC.sourceFile x’
    In a stmt of a 'do' block: DCC.sourceFile x $= transducer
    In the expression:
      do { DCC.sourceFile x $= transducer;
           yield $ Chunk $ fromLazyByteString "," }

gistfile3.hs

{-# LANGUAGE OverloadedStrings #-}
module Test where

import           Blaze.ByteString.Builder  (Builder)
import           Blaze.ByteString.Builder  (fromLazyByteString)
import           Conduit                   (Flush)
import           Conduit                   (Source)
import           Conduit                   (Flush (..))
import           Conduit                   (yield)
import           Conduit                   (($=))
import           Conduit                   (ConduitM)
import qualified Conduit                   as DCC
import           Data.Text                 (Text)
import           Filesystem.Path.CurrentOS (FilePath)
import           Prelude                   hiding (FilePath)

streamFiles ::  IO () -> [FilePath] -> Source IO (Flush Builder)
streamFiles ready filepaths  = do
  --liftIO $ ready
  yield $ Chunk $ fromLazyByteString "{"
  mapM_ (\x -> do
            DCC.sourceFile x $= transducer
            yield $ Chunk $ fromLazyByteString ",\n")
    filepaths
  yield $ Chunk $ fromLazyByteString "}"

transducer :: ConduitM Text (Flush Builder) m1 a0
transducer = undefined

streamFiles ::  IO () -> [FilePath] -> Source IO (Flush Builder)
streamFiles ready filepaths  = do
  --liftIO $ ready
  yield $ Chunk $ fromLazyByteString "{"
  mapM_ (\x -> do
            -- my god this is a huge hack, but i cannot for the life
            -- of me make DCC.sourceFile do something useful.
            f <- liftIO $ BL.readFile (show x)
            yield $ Chunk $ fromLazyByteString f
            yield $ Chunk $ fromLazyByteString ",\n")
    filepaths
  yield $ Chunk $ fromLazyByteString "}"

does what i want, but not relying on lazy bytestrings is half the reason to use conduit in the first place.

{-# LANGUAGE OverloadedStrings #-}
module Test where

import Blaze.ByteString.Builder (Builder)
import Blaze.ByteString.Builder (fromLazyByteString)
import Data.Conduit (Flush)
import Data.Conduit (Source)
import Data.Conduit (Flush (..))
import Data.Conduit (yield)
import Data.Conduit (($=))
import Data.Conduit (ConduitM)
import qualified Data.Conduit.Binary as DCC
import Data.ByteString (ByteString)
import Control.Monad.Trans.Resource


streamFiles :: MonadResource m => IO () -> [FilePath] -> Source m (Flush Builder)
streamFiles ready filepaths  = do
  --liftIO $ ready
  yield $ Chunk $ fromLazyByteString "{"
  mapM_ (\x -> do
            _ <- DCC.sourceFile x $= transducer
            yield $ Chunk $ fromLazyByteString ",\n")
        filepaths
  yield $ Chunk $ fromLazyByteString "}"

transducer :: ConduitM ByteString (Flush Builder) m1 a0
transducer = undefined