**Packages**- mtl
- transformers

A monad transformer that combines ReaderT, WriterT and StateT. This version is strict; for a lazy version, see Control.Monad.Trans.RWS.Lazy, which has the same interface.

Strict state monads, passing an updatable state through a computation. See below for examples.
In this version, sequencing of computations is strict. For a lazy version, see Control.Monad.Trans.State.Lazy, which has the same interface.
Some computations may not require the full power of state transformers:
* For a read-only state, see Control.Monad.Trans.Reader.
* To accumulate a value without using it on the way, see Control.Monad.Trans.Writer.

The strict WriterT monad transformer, which adds collection of outputs (such as a count or string output) to a given monad.
This version builds its output strictly; for a lazy version, see Control.Monad.Trans.Writer.Lazy, which has the same interface.
This monad transformer provides only limited access to the output during the computation. For more general access, use Control.Monad.Trans.State instead.