Add AVar.modify helper function

Author: errfrom

src/Internal/Lib/AVar.purs

@@ -0,0 +1,23 @@
+module HydraSdk.Internal.Lib.AVar
+  ( modify
+  ) where
+
+import Prelude
+
+import Control.Monad.Error.Class (class MonadError, catchError, throwError)
+import Effect.AVar (AVar)
+import Effect.Aff.AVar (put, take) as AVar
+import Effect.Aff.Class (class MonadAff, liftAff)
+
+modify
+  :: forall (m :: Type -> Type) (e :: Type) (a :: Type)
+   . MonadAff m
+  => MonadError e m
+  => (a -> m a)
+  -> AVar a
+  -> m a
+modify f avar = do
+  prev <- liftAff $ AVar.take avar
+  new <- catchError (f prev) \err -> liftAff (AVar.put prev avar) *> throwError err
+  liftAff $ AVar.put new avar
+  pure new

src/Lib.purs

@@ -1,7 +1,10 @@
 module HydraSdk.Lib
-  ( module ExportCodec
+  ( module ExportAVar
+  , module ExportCodec
   ) where
 
+import HydraSdk.Internal.Lib.AVar (modify) as ExportAVar
+
 import HydraSdk.Internal.Lib.Codec
   ( class FromVariantGeneric
   , class ToVariantGeneric