Fresh.hs

{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{- | This effect provides source to an infinite source of 'Int' values, suitable for generating "fresh" values to uniquely identify data without needing to invoke random numbers or impure IO.

Predefined carriers:

* "Control.Carrier.Fresh.Church"
* "Control.Carrier.Fresh.Strict"
-}
module Control.Effect.Fresh
( -- * Fresh effect
  Fresh(..)
, fresh
  -- * Re-exports
, Algebra
, Has
, run
) where

import Control.Algebra
import Data.Kind (Type)

-- | @since 0.1.0.0
data Fresh (m :: Type -> Type) k where
  Fresh :: Fresh m Int


-- | Produce a fresh (i.e. unique) 'Int'.
--
-- @
-- m '>>' 'fresh' ≠ m '>>' 'fresh' '>>' 'fresh'
-- @
--
-- @since 0.1.0.0
fresh :: Has Fresh sig m => m Int
fresh = send Fresh
{-# INLINE fresh #-}