I don’t use ST much, but sometimes it is just the best solution. This can be in many scenarios: There are already well-known, efficient ways to solve a problem. Quicksort is a perfect example of this. It is known for its speed and in-place behavior, which cannot be imitated by pure code very well. You … Read more
I’ve written multiple compilers in Haskell, and a state monad is a reasonable solution to many compiler problems. But you want to keep it abstract—don’t make it obvious you’re using a monad. Here’s an example from the Glasgow Haskell Compiler (which I did not write; I just work around a few edges), where we build … Read more
I assume, scalaz 7.0.x and the following imports (look at answer history for scalaz 6.x): import scalaz._ import Scalaz._ The state type is defined as State[S, A] where S is type of the state and A is the type of the value being decorated. The basic syntax to create a state value makes use of … Read more
The State Monad : a model of mutable state The State monad is a purely functional environment for programs with state, with a simple API: get put Documentation in the mtl package. The State monad is commonly used when needing state in a single thread of control. It doesn’t actually use mutable state in its … Read more