withState -package:massiv

withState f m executes action m on a state modified by applying f.

• withState f m = modify f >> m

>>> runPureEff $ withState 10 $ \st -> do
n <- get st
pure (s -> (2 * n, s))
(20,10)

>>> runPureEff $ withState 10 $ \st -> do
n <- get st
pure (s -> (2 * n, s))
(20,10)

withStateT f m executes action m on a state modified by applying f.

• withStateT f m = modify f >> m

withStateT f m executes action m on a state modified by applying f.

• withStateT f m = modify f >> m

Opens a prepared statement, executes an action using this statement, and closes the statement, even in the presence of exceptions.

Bracket prepare and finalize. Useful for stepping multiple times through a Statement

runPureEff $ withStateSource $ \source -> do
n <- newState source 5
total <- newState source 0

withJump $ \done -> forever $ do
n' <- get n
modify total (+ n')
when (n' == 0) $ jumpTo done
modify n (subtract 1)

get total
15

runPureEff $ withStateSource $ \source -> do
n <- newState source 5
total <- newState source 0

withJump $ \done -> forever $ do
n' <- get n
modify total (+ n')
when (n' == 0) $ jumpTo done
modify n (subtract 1)

get total
15

Set a flag in the parser to True before running a parser, then set the flag's value to False.

Evaluate the inner monad of a stream using the supplied stateful runner function and the initial state. The state returned by an invocation of the runner is supplied as input state to the next invocation.

Run a stateful parser with some initial state on a text. See also: runTextParser, runJournalParser.