feat: Pipes.Node.FS, Pipes.Node.Buffer, etc.

src/Pipes.Util.purs

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+module Pipes.Util where
+
+import Prelude
+
+import Control.Monad.Rec.Class (whileJust)
+import Control.Monad.ST.Class (liftST)
+import Control.Monad.ST.Ref as STRef
+import Data.Maybe (Maybe(..))
+import Effect.Class (class MonadEffect, liftEffect)
+import Pipes (await, yield)
+import Pipes.Core (Pipe)
+
+-- | Yields a separator value `sep` between received values
+-- |
+-- | ```purescript
+-- | toList $ (yield "a" *> yield "b" *> yield "c") >-> intersperse ","
+-- | -- "a" : "," : "b" : "," : "c" : Nil
+-- | ```
+intersperse :: forall m a. MonadEffect m => a -> Pipe (Maybe a) (Maybe a) m Unit
+intersperse sep = do
+  isFirst <- liftEffect $ liftST $ STRef.new true
+  whileJust do
+    ma <- await
+    isFirst' <- liftEffect $ liftST $ STRef.read isFirst
+    case ma of
+      Just a
+        | isFirst' -> do
+          void $ liftEffect $ liftST $ STRef.write false isFirst
+          yield $ Just a
+        | otherwise -> yield (Just sep) *>  yield (Just a)
+      Nothing -> yield Nothing
+    pure $ void ma