From 4e987026148fe65c323afbc93cd560c07bf06b3f Mon Sep 17 00:00:00 2001
From: Yale AI Dept <ai@nebula.cs.yale.edu>
Date: Wed, 14 Jul 1993 13:08:00 -0500
Subject: Import to github.

---
 progs/prelude/PreludeIOMonad.hs | 60 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 progs/prelude/PreludeIOMonad.hs

(limited to 'progs/prelude/PreludeIOMonad.hs')

diff --git a/progs/prelude/PreludeIOMonad.hs b/progs/prelude/PreludeIOMonad.hs
new file mode 100644
index 0000000..9a45606
--- /dev/null
+++ b/progs/prelude/PreludeIOMonad.hs
@@ -0,0 +1,60 @@
+module IOMonad (State, IO(..)) where
+
+import IOMonadPrims
+
+{- I use data instead of type so that IO can be abstract. For efficiency,
+   IO can be annotated as a strict constructor.
+-}
+
+type IO a = State -> (State, a)
+
+data State = State
+
+-- The rest of this file is unnecessary at the moment since
+-- unitIO & bindIO are primitives and we're not using the rest of this
+
+{- Implemented as a primitives: 
+bindIO :: IO a -> (a -> IO b) -> IO b
+bindIO (IO m) (IO k) = IO (\s0 -> let (s1, a) = m s0 in k a s1) -}
+
+unitIO :: a -> IO a
+unitIO x = IO (\s -> (s, x))
+
+-}
+
+{-  Not currently used:
+pureIO :: IO a -> a
+pureIO (IO m) = let (s, x) = m State in x
+
+-- execIO executes a program of type IO ().
+execIO :: IO () -> State
+execIO (IO m) = let (s, x) = m State in s
+
+infixr  1 =:
+infixr  1 ?
+
+-- assignment
+(=:)      :: a -> Var a -> IO ()
+x =: v  = IO (\s -> (update v x s, ()))
+
+-- reader
+(?)       :: Var a -> (a -> IO b) -> IO b
+v ? k   = IO (\s -> (s, readVar v s)) `bindIO` k
+
+-- new
+newvar    :: IO (Var a)
+newvar = IO allocVar
+
+instance Eq (Var a) where
+   x == y = eqVar x y
+-}
+
+
+
+
+
+
+
+
+
+
-- 
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