What are some examples of using transformers in Haskell?

Can you give me some examples of using transformers in Haskell?

Sure! Haskell transformers are used to combine different monads. For example, you can use the StateT transformer to add stateful computations to an existing monad.

How does the StateT transformer work?

The StateT transformer takes a state and a computation, allowing you to pass the state through the computation. It can be used with other monads like IO or Maybe.

Can you show me a simple code example?

Absolutely! Here's a simple example:

import Control.Monad.Trans.State

type Counter = State Int

increment :: Counter ()
increment = do
    n <- get
    put (n + 1)

This code defines a stateful computation that increments an integer.

What other transformers are commonly used?

Other commonly used transformers include MaybeT for handling optional values and ExceptT for error handling.