Test cleanup: make 1-to-1 correspondence between source modules and test modules

core/docs/Changelog.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+* Fixed `Stream.postscanl` to omit the output of a scan that terminates without
+  consuming any input (e.g. `Scanl.take 0`).
 * Breaking: In `FileSystem.Path` module the default for `eqPath` changed
   on Windows to case-sensitive comparison.
 * Breaking: A leading "." component (e.g. "." or "./x") is no longer

core/src/Streamly/Internal/Data/Stream/Transform.hs

@@ -537,17 +537,24 @@ data ScanState s f = ScanInit s | ScanDo s !f | ScanDone
 -- Unfortunately, we cannot define lazy scans because the Partial constructor
 -- itself is strict.
 
--- | Postscan a stream using the given fold. A postscan omits the initial
--- (default) value of the accumulator and includes the final value.
+-- | Postscan a stream using the given scan. A postscan emits one output per
+-- input element, omitting the initial value of the accumulator. Equivalently,
+-- @postscanl s = 'Data.List.drop' 1 . 'scanl' s@.
 --
 -- >>> Stream.toList $ Stream.postscanl Scanl.latest (Stream.fromList [])
 -- []
 --
--- Compare with 'scan' which includes the initial value as well:
+-- Compare with 'scanl' which additionally emits the initial value:
 --
 -- >>> Stream.toList $ Stream.scanl Scanl.latest (Stream.fromList [])
 -- [Nothing]
 --
+-- A scan that terminates at the initial step (e.g. @Scanl.take 0@) consumes no
+-- input, so the postscan is empty:
+--
+-- >>> Stream.toList $ Stream.postscanl (Scanl.take 0 Scanl.toList) (Stream.fromList [1,2,3::Int])
+-- []
+--
 -- The following example extracts the input stream up to a point where the
 -- running average of elements is no more than 10:
 --
@@ -575,7 +582,12 @@ postscanl (Scanl fstep initial extract final) (Stream sstep state) =
         return
             $ case res of
                   FL.Partial fs -> Skip $ ScanDo st fs
-                  FL.Done b -> Yield b ScanDone
+                  -- A scan that is Done at the initial step has consumed no
+                  -- input, so a postscan (one output per consumed input) emits
+                  -- nothing. This keeps the invariant
+                  -- @postscanl s = drop 1 . scanl s@: the initial value is
+                  -- always dropped, whether it comes from a Partial or a Done.
+                  FL.Done _ -> Stop
     step gst (ScanDo st fs) = do
         res <- sstep (adaptState gst) st
         case res of

streamly.cabal

@@ -129,7 +129,9 @@ extra-source-files:
     test/Streamly/Test/Data/*.hs
     test/Streamly/Test/Data/Array/*.hs
     test/Streamly/Test/Data/MutArray/*.hs
+    test/Streamly/Test/Data/Parser/*.hs
     test/Streamly/Test/Data/ParserK/*.hs
+    test/Streamly/Test/Data/RingArray/*.hs
     test/Streamly/Test/Data/Stream/*.hs
     test/Streamly/Test/Data/Stream/MkType/*.hs
     test/Streamly/Test/Data/Stream/Prelude/*.hs
@@ -145,7 +147,6 @@ extra-source-files:
     test/Streamly/Test/Prelude.hs
     test/Streamly/Test/Prelude/*.hs
     test/Streamly/Test/Unicode/*.hs
-    test/Streamly/Test/Serialize/*.hs
     test/Streamly/Test/Data/Scanl/*.hs
     test/Streamly/Test/Data/Fold/*.hs
     test/Streamly/Test/Unicode/ucd/NormalizationTest.txt
@@ -154,8 +155,7 @@ extra-source-files:
     test/lib/Streamly/Test/Common.hs
     test/lib/Streamly/Test/Control/Exception/Common.hs
     test/lib/Streamly/Test/Prelude/Common.hs
-    test/lib/Streamly/Test/Data/Parser/CommonTests.hs
-    test/lib/Streamly/Test/Data/Parser/CommonUtilities.hs
+    test/lib/Streamly/Test/Data/Parser/*.hs
     test/streamly-tests.cabal
     test/version-bounds.hs
 

test/Streamly/Test/Serialize/Serializable.hs → test/Streamly/Test/Data/Binary.hs

@@ -194,7 +194,7 @@ charLatin1 = forAll (chooseChar (unsafeChr 0, unsafeChr 255)) $ \x ->
         monadicIO $ action x Encoder.charLatin1  Decoder.charLatin1
 
 moduleName :: String
-moduleName = "Serialize.Serializable"
+moduleName = "Data.Binary"
 
 main :: IO ()
 main =

test/Streamly/Test/Data/Fold.hs

@@ -13,13 +13,10 @@ import qualified Streamly.Test.Data.Fold.Container as Container
 import qualified Streamly.Test.Data.Fold.Exception as Exception
 import qualified Streamly.Test.Data.Fold.Tee as Tee
 import qualified Streamly.Test.Data.Fold.Type as Type
-import qualified Streamly.Test.Data.Fold.Window as Window
-
 main :: IO ()
 main = do
     Type.main
     Combinators.main
     Container.main
-    Window.main
     Exception.main
     Tee.main