:: Monad m => m Bool -> m () -> m () -package:IfElse

Monadic version of when, taking the condition in the monad

Monadic version of unless, taking the condition in the monad

Like when, but where the test can be monadic.

Like unless, but where the test can be monadic.

Monadic version of unless. Reverse of whenM. Conditionally don't execute the provided action.

>>> unlessM (pure False) $ putTextLn "No text :("
No text :(

>>> unlessM (pure True) $ putTextLn "Yes text :)"

Monadic version of when. Conditionally executes the provided action.

>>> whenM (pure False) $ putTextLn "No text :("

>>> whenM (pure True)  $ putTextLn "Yes text :)"
Yes text :)

>>> whenM (Just True) (pure ())
Just ()

>>> whenM (Just False) (pure ())
Just ()

>>> whenM Nothing (pure ())
Nothing

Run the second value if the first value returns True

Run the second value if the first value returns False

A monadic-conditional version of the when guard.

A monadic-conditional version of the unless guard.

Only perform the action if the predicate returns True. Since 0.9.2

Only perform the action if the predicate returns False. Since 0.9.2

Monadic version of unless.

>>> unlessM (pure False) $ putTextLn "No text :("
No text :(

>>> unlessM (pure True) $ putTextLn "Yes text :)"

Monadic version of when.

>>> whenM (pure False) $ putTextLn "No text :("

>>> whenM (pure True)  $ putTextLn "Yes text :)"
Yes text :)

>>> whenM (Just True) (pure ())
Just ()

>>> whenM (Just False) (pure ())
Just ()

>>> whenM Nothing (pure ())
Nothing

when with a monadic predicate.

unless with a monadic predicate.

Variant of when that takes a monadic action for the condition.

Variant of unless that takes a monadic action for the condition.

This is the whenM operator, With it you can write doesItExists ?> removeIt instead of do {e <- doesItExists; when e removeIt}. There's not unlessM version, so you have to use not.

not <$> doesItExists ?> createIt

Execute an action repeatedly as long as the given boolean expression returns True. The condition is evaluated before the loop body. Discards results.

p --> x. If p returns True, execute the ManageHook.

(-->) :: Monoid m => Query Bool -> Query m -> Query m -- a simpler type

A whenX/whenM that accepts a monoidal return value.

Run the action if the given monadic condition becomes True.