Mini.Transformers.WriterT

Extension of a monad with a write-only environment

Type

data WriterT w m a

A monad with monoidal write-only type w, inner monad m, and return type a

Instances

Monoid w => MonadTrans (WriterT w)

Defined in Mini.Transformers.WriterT

Methods

lift :: Monad m => m a -> WriterT w m a

(Monad m, Alternative m, Monoid w) => Alternative (WriterT w m)

Defined in Mini.Transformers.WriterT

Methods

empty :: WriterT w m a

(<|>) :: WriterT w m a -> WriterT w m a -> WriterT w m a

some :: WriterT w m a -> WriterT w m [a]

many :: WriterT w m a -> WriterT w m [a]

(Monad m, Monoid w) => Applicative (WriterT w m)

Defined in Mini.Transformers.WriterT

Methods

pure :: a -> WriterT w m a

(<*>) :: WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b

liftA2 :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c

(*>) :: WriterT w m a -> WriterT w m b -> WriterT w m b

(<*) :: WriterT w m a -> WriterT w m b -> WriterT w m a

(Monad m, Monoid w) => Functor (WriterT w m)

Defined in Mini.Transformers.WriterT

Methods

fmap :: (a -> b) -> WriterT w m a -> WriterT w m b

(<$) :: a -> WriterT w m b -> WriterT w m a

(Monad m, Monoid w) => Monad (WriterT w m)

Defined in Mini.Transformers.WriterT

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b

return :: a -> WriterT w m a

Writing

tell :: Monad m => w -> WriterT w m ()

Append the given value to the output

Runners

runWriterT :: WriterT w m a -> m (a, w)

Unwrap a WriterT