diff -ru3 IOSpec-0.2.5-old/src/Test/IOSpec/STM.hs IOSpec-0.2.5/src/Test/IOSpec/STM.hs
--- IOSpec-0.2.5-old/src/Test/IOSpec/STM.hs	2015-04-17 21:32:51.062498481 +0300
+++ IOSpec-0.2.5/src/Test/IOSpec/STM.hs	2015-04-17 21:39:50.451032159 +0300
@@ -23,6 +23,7 @@
 import Data.Dynamic
 import Data.Maybe (fromJust)
 import Control.Monad.State
+import Control.Monad (ap)
 
 -- The 'STMS' data type and its instances.
 --
@@ -67,14 +68,18 @@
   fmap _ Retry              = Retry
   fmap f (OrElse io1 io2)   = OrElse (fmap f io1) (fmap f io2)
 
+instance Applicative STM where
+  pure  = STMReturn
+  (<*>) = ap
+
 instance Monad STM where
-    return                = STMReturn
-    STMReturn a >>= f     = f a
-    NewTVar d g >>= f     = NewTVar d (\l -> g l >>= f)
-    ReadTVar l g >>= f    = ReadTVar l (\d -> g d >>= f)
-    WriteTVar l d p >>= f = WriteTVar l d (p >>= f)
-    Retry >>= _           = Retry
-    OrElse p q >>= f      = OrElse (p >>= f) (q >>= f)
+  return                = STMReturn
+  STMReturn a >>= f     = f a
+  NewTVar d g >>= f     = NewTVar d (\l -> g l >>= f)
+  ReadTVar l g >>= f    = ReadTVar l (\d -> g d >>= f)
+  WriteTVar l d p >>= f = WriteTVar l d (p >>= f)
+  Retry >>= _           = Retry
+  OrElse p q >>= f      = OrElse (p >>= f) (q >>= f)
 
 -- | A 'TVar' is a shared, mutable variable used by STM.
 newtype TVar a = TVar Loc
diff -ru3 IOSpec-0.2.5-old/src/Test/IOSpec/Types.hs IOSpec-0.2.5/src/Test/IOSpec/Types.hs
--- IOSpec-0.2.5-old/src/Test/IOSpec/Types.hs	2015-04-17 21:32:51.062498481 +0300
+++ IOSpec-0.2.5/src/Test/IOSpec/Types.hs	2015-04-17 21:37:02.306575081 +0300
@@ -15,6 +15,8 @@
   , inject
   ) where
 
+import Control.Monad (ap)
+
 -- | A value of type 'IOSpec' @f@ @a@ is either a pure value of type @a@
 -- or some effect, determined by @f@. Crucially, 'IOSpec' @f@ is a
 -- monad, provided @f@ is a functor.
@@ -26,6 +28,10 @@
   fmap f (Pure x)   = Pure (f x)
   fmap f (Impure t) = Impure (fmap (fmap f) t)
 
+instance (Functor f) => Applicative (IOSpec f) where
+  pure             = Pure
+  (<*>)            = ap
+
 instance (Functor f) => Monad (IOSpec f) where
   return           = Pure
   (Pure x) >>= f   = f x
@@ -61,4 +67,4 @@
     inj = Inr . inj
 
 inject :: (g :<: f) => g (IOSpec f a) -> IOSpec f a
-inject = Impure . inj
\ No newline at end of file
+inject = Impure . inj
diff -ru3 IOSpec-0.2.5-old/src/Test/IOSpec/VirtualMachine.hs IOSpec-0.2.5/src/Test/IOSpec/VirtualMachine.hs
--- IOSpec-0.2.5-old/src/Test/IOSpec/VirtualMachine.hs	2015-04-17 21:32:51.062498481 +0300
+++ IOSpec-0.2.5/src/Test/IOSpec/VirtualMachine.hs	2015-04-17 21:39:47.222044580 +0300
@@ -43,6 +43,7 @@
 import qualified Data.Stream as Stream
 import Test.IOSpec.Types
 import Test.QuickCheck
+import Control.Monad (ap)
 
 type Data         = Dynamic
 type Loc          = Int
@@ -211,6 +212,10 @@
   fmap f (Print c t) = Print c (fmap f t)
   fmap _ (Fail msg) = Fail msg
 
+instance Applicative Effect where
+  pure = Done
+  (<*>) = ap
+
 instance Monad Effect where
   return = Done
   (Done x) >>= f = f x