hasql-demo.hs

#!/usr/bin/env stack
-- stack --install-ghc runghc --package hasql

{-# LANGUAGE OverloadedStrings #-}

import           Data.Monoid            ((<>))
import           Hasql.Connection       (acquire, release, settings)
import           Hasql.Decoders         (int8, singleRow, value)
import           Hasql.Encoders         (unit)
import           Hasql.Query            (statement)
import           Hasql.Session          (query, run)

main :: IO ()
main = do
  let host      = "localhost"
      port      = 5432
      user      = "andrew"
      pass      = "supersecret"
      db        = "postgres"
      settings' = settings host port user pass db
      q         = statement "SELECT COUNT(*) FROM foo"
                            unit -- we have no parameters to encode
                            (singleRow (value int8)) -- we decode an int8 (Int64) from a single row
                            False -- don't prepare the statement
      session   = query () q
      printResult n = putStrLn $ "Have " <> show n <> " rows"
  connE <- acquire settings'
  case connE of
    Left e -> print e
    Right conn -> do
      rE <- run session conn
      either print printResult rE
      release conn