compiler/Unique.hs · elk

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elk/compiler/Unique.hs

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1{-# LANGUAGE GeneralizedNewtypeDeriving #-}

2module Unique (guid, set, run, runAt, Unique) where

4import Control.Monad.State (evalState, State, get, put)

6-- Wrapper around State monad.

7newtype Unique a = U { runU :: State Int a }

8 deriving (Monad)

10-- Get the next GUID, incrementing the counter.

11guid :: Unique Int

12guid = U $ do n <- get

13 put (n + 1)

14 return n

16set n = U (put n)

18run = runAt 0

19runAt n x = evalState (runU x) n