compiler/Model/Guid.hs · elk

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1{-# LANGUAGE GeneralizedNewtypeDeriving #-}

2module Guid (guid, set, run, runAt, GuidCounter) where

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

6-- Wrapper around State monad.

7newtype GuidCounter a = GC { runGC :: State Int a }

8 deriving (Monad)

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

11guid :: GuidCounter Int

12guid = GC $ do n <- get

13 put (n + 1)

14 return n

16set n = GC (put n)

18run = runAt 0

19runAt n x = evalState (runGC x) n