https://github.com/nikita-volkov/hasql/issues/79

Main.hs

import qualified Data.Text
import qualified Data.Text.Encoding
import qualified Hasql.Batch
import qualified Hasql.Connection
import qualified Hasql.DecodeResult
import qualified Hasql.Statement

main :: IO ()
main = do

  let utf8 = Data.Text.Encoding.encodeUtf8 . Data.Text.pack
  let host = utf8 "127.0.0.1"
  let port = 5432
  let settings = Hasql.Connection.TCPConnectionSettings host port
  let username = utf8 "postgres"
  let password = mempty
  let database = Just (utf8 "postgres")
  let handler = print

  putStrLn "Connecting ..."
  connectionResult <- Hasql.Connection.open settings username password database handler
  connection <- case connectionResult of
    Left problem -> fail (show problem)
    Right connection -> pure connection
  putStrLn "Connected."

  let template = utf8 "select 1"
  let encoder = mempty
  let decoder = Hasql.DecodeResult.ignore
  let statement = Hasql.Statement.prepared template encoder decoder
  let batch = Hasql.Batch.statement statement ()

  putStrLn "Querying ..."
  -- This statement hangs forever.
  sessionResult <- Hasql.Connection.batch connection batch
  case sessionResult of
    Left problem -> fail (show problem)
    Right unit -> pure unit
  putStrLn "Queried."

  putStrLn "Closing ..."
  Hasql.Connection.close connection
  putStrLn "Closed."

package.yaml

name: hasql-example
version: 0.0.0

executables:
  hasql-example:
    dependencies:
      - base
      - hasql
      - text
    ghc-options:
      - -rtsopts
      - -threaded
      - -Wall
    main: Main.hs

stack.yaml

resolver: ghc-8.2.1

extra-deps:
  - aeson-1.2.3.0
  - attoparsec-0.13.2.0
  - base-compat-0.9.3
  - base-orphans-0.6
  - base-prelude-1.2.0.1
  - basement-0.0.3
  - bifunctors-5.4.2
  - binary-parser-0.5.5
  - bug-1.0.1
  - bytestring-strict-builder-0.4.5
  - cabal-doctest-1.0.2
  - case-insensitive-1.2.0.10
  - cereal-0.5.4.0
  - charset-0.3.7.1
  - comonad-5.0.2
  - contravariant-1.4
  - cryptohash-md5-0.11.100.1
  - cryptohash-sha1-0.11.100.1
  - cryptonite-0.22
  - data-bword-0.1.0.1
  - data-checked-0.3
  - data-default-class-0.1.2.0
  - data-dword-0.3.1.1
  - data-endian-0.1.1
  - data-serializer-0.3
  - data-textual-0.3.0.2
  - deque-0.2
  - distributive-0.5.3
  - dlist-0.8.0.3
  - entropy-0.3.8
  - exceptions-0.8.3
  - focus-0.1.5.2
  - foldl-1.3.2
  - foundation-0.0.16
  - free-4.12.4
  - hashable-1.2.6.1
  - hasql-0.20.0.1
  - integer-logarithms-1.0.2
  - list-t-1.0.0.1
  - loch-th-0.2.1
  - managed-1.0.5
  - math-functions-0.2.1.0
  - memory-0.14.8
  - mmorph-1.1.0
  - monad-control-1.0.2.2
  - mtl-2.2.1
  - mwc-random-0.13.6.0
  - network-2.6.3.2
  - network-info-0.2.0.8
  - network-ip-0.3.0.2
  - parsec-3.1.11
  - parsers-0.12.7
  - partial-handler-1.0.2
  - persistent-vector-0.1.1
  - placeholders-0.1
  - postgresql-binary-0.12.1
  - prelude-extras-0.4.0.3
  - primitive-0.6.2.0
  - profunctors-5.2.1
  - random-1.1
  - scanner-0.2
  - scientific-0.3.5.2
  - semigroupoids-5.2.1
  - semigroups-0.18.3
  - slave-thread-1.0.2
  - StateVar-1.1.0.4
  - stm-2.4.4.1
  - stm-containers-0.2.16
  - tagged-0.8.5
  - text-1.2.2.2
  - text-latin1-0.3
  - text-printer-0.5
  - th-abstraction-0.2.6.0
  - time-locale-compat-0.1.1.3
  - transformers-base-0.4.4
  - transformers-compat-0.5.1.4
  - type-hint-0.1
  - unordered-containers-0.2.8.0
  - uuid-1.3.13
  - uuid-types-1.0.3
  - vector-0.12.0.1
  - vector-builder-0.3.3.1
  - vector-th-unbox-0.2.1.6
  - void-0.7.2

flags:
  time-locale-compat:
    old-locale: false