Safe Haskell	Safe-Inferred
Language	GHC2021

Database.DuckDB.Internal

Contents

Error reporting
Monad
Version

Synopsis

type DuckDBError = String
isDuckDBError :: DuckDBState -> Bool
newtype DuckDBMonad a = DuckDBMonad {
- runDuckDBMonad :: ExceptT DuckDBError IO a
}
liftIO :: MonadIO m => IO a -> m a
liftIOEither :: IO (Either DuckDBError a) -> DuckDBMonad a
runDuckDB :: DuckDBMonad a -> IO (Either DuckDBError a)
version :: DuckDBMonad String

Error reporting

type DuckDBError = String Source #

isDuckDBError :: DuckDBState -> Bool Source #

Monad

newtype DuckDBMonad a Source #

Constructors

DuckDBMonad
Fields runDuckDBMonad :: ExceptT DuckDBError IO a

Instances

Instances details

MonadIO DuckDBMonad Source #
Instance details Defined in Database.DuckDB.Internal Methods liftIO :: IO a -> DuckDBMonad a #
Applicative DuckDBMonad Source #
Instance details Defined in Database.DuckDB.Internal Methods pure :: a -> DuckDBMonad a # (<>) :: DuckDBMonad (a -> b) -> DuckDBMonad a -> DuckDBMonad b # liftA2 :: (a -> b -> c) -> DuckDBMonad a -> DuckDBMonad b -> DuckDBMonad c # (>) :: DuckDBMonad a -> DuckDBMonad b -> DuckDBMonad b # (<*) :: DuckDBMonad a -> DuckDBMonad b -> DuckDBMonad a #
Functor DuckDBMonad Source #
Instance details Defined in Database.DuckDB.Internal Methods fmap :: (a -> b) -> DuckDBMonad a -> DuckDBMonad b # (<$) :: a -> DuckDBMonad b -> DuckDBMonad a #
Monad DuckDBMonad Source #
Instance details Defined in Database.DuckDB.Internal Methods (>>=) :: DuckDBMonad a -> (a -> DuckDBMonad b) -> DuckDBMonad b # (>>) :: DuckDBMonad a -> DuckDBMonad b -> DuckDBMonad b # return :: a -> DuckDBMonad a #
MonadError DuckDBError DuckDBMonad Source #
Instance details Defined in Database.DuckDB.Internal Methods throwError :: DuckDBError -> DuckDBMonad a # catchError :: DuckDBMonad a -> (DuckDBError -> DuckDBMonad a) -> DuckDBMonad a #

liftIO :: MonadIO m => IO a -> m a #

Lift a computation from the IO monad. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

Expand

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

Had we omitted liftIO, we would have ended up with this error:

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

The important part here is the mismatch between StateT s IO () and IO ().

Luckily, we know of a function that takes an IO a and returns an (m a): liftIO, enabling us to run the program and see the expected results:

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

liftIOEither :: IO (Either DuckDBError a) -> DuckDBMonad a Source #

runDuckDB :: DuckDBMonad a -> IO (Either DuckDBError a) Source #

Version

version :: DuckDBMonad String Source #