Make the inject function of Unfold pure

.github/workflows/freebsd.yml

@@ -0,0 +1,89 @@
+# FreeBSD CI
+#
+# FreeBSD is not a native GitHub Actions runner, so this workflow runs
+# the build inside a VM via vmactions/freebsd-vm. It is kept separate
+# from haskell.yml because the cache/restore step model in that
+# workflow (hackage index, ghcup, deps caches) does not apply inside
+# the VM.
+
+name: FREEBSD
+
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    name: >-
+      freebsd-${{ matrix.release }}
+      ${{ matrix.command }}
+      ${{ matrix.ghc_version }}
+    runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.ignore_error }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - release: "14.3"
+            command: cabal
+            ghc_version: 9.14.1
+            ignore_error: true
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Build on FreeBSD
+      uses: vmactions/freebsd-vm@v1
+      env:
+        PACKCHECK_COMMAND: ${{ matrix.command }}
+        GHCVER: ${{ matrix.ghc_version }}
+        # For updating see: https://downloads.haskell.org/~ghcup/
+        GHCUP_VERSION: 0.1.50.2
+        LC_ALL: C.UTF-8
+        CABAL_REINIT_CONFIG: y
+        CABAL_CHECK_RELAX: y
+        CABAL_PROJECT: cabal.project
+        DISABLE_BENCH: "y"
+        DISABLE_DOCS: "y"
+        DISABLE_SDIST_BUILD: "y"
+        DISABLE_DIST_CHECKS: "y"
+        PACKCHECK: "./packcheck.sh"
+        PACKCHECK_GITHUB_URL: "https://raw.githubusercontent.com/composewell/packcheck"
+        PACKCHECK_GITHUB_COMMIT: "b3743510c7c26f83254ffd9ef91bcd71560cff05"
+      with:
+        release: ${{ matrix.release }}
+        usesh: true
+        copyback: false
+        envs: >-
+          PACKCHECK_COMMAND GHCVER GHCUP_VERSION LC_ALL
+          CABAL_REINIT_CONFIG CABAL_CHECK_RELAX CABAL_PROJECT
+          DISABLE_BENCH DISABLE_DOCS DISABLE_SDIST_BUILD DISABLE_DIST_CHECKS
+          PACKCHECK PACKCHECK_GITHUB_URL PACKCHECK_GITHUB_COMMIT
+        prepare: |
+          pkg update
+          pkg install -y gmake
+          pkg install -y bash
+          pkg install -y git
+          pkg install -y gmp
+        run: |
+          if test ! -e "$PACKCHECK"
+          then
+            if test -z "$PACKCHECK_GITHUB_COMMIT"
+            then
+              echo "PACKCHECK_GITHUB_COMMIT is not specified." >&2
+              exit 1
+            fi
+            PACKCHECK_URL=${PACKCHECK_GITHUB_URL}/${PACKCHECK_GITHUB_COMMIT}/packcheck.sh
+            curl --fail -sL -o "$PACKCHECK" $PACKCHECK_URL || exit 1
+            chmod +x $PACKCHECK
+          elif test ! -x "$PACKCHECK"
+          then
+            chmod +x $PACKCHECK
+          fi
+          # Use "bash -c" instead of invoking directly to preserve quoted
+          # arguments in PACKCHECK_COMMAND e.g. DOCSPEC_OPTIONS="--timeout 60".
+          # Direct invocation would word-split on spaces inside quoted values.
+          bash -c "$PACKCHECK $PACKCHECK_COMMAND"

.hlint.yaml

@@ -48,6 +48,7 @@
     [ --cpp-include=src
     , --cpp-include=src/Streamly/Internal/Data/Stream
     , --cpp-include=core/src/Streamly/Internal/Data/Array
+    , --cpp-include=core/src/doctest
     , --cpp-include=test
     , --cpp-define=CABAL_OS_LINUX
     , --cpp-define=linux_HOST_OS

benchmark/streamly-benchmarks.cabal

@@ -260,8 +260,8 @@ benchmark Data.Array.Generic
     buildable: False
   else
     buildable: True
-  if flag(limit-build-mem) && !flag(fusion-plugin)
-    ghc-options: +RTS -M500M -RTS
+  if flag(limit-build-mem)
+    ghc-options: +RTS -M600M -RTS
 
 benchmark Data.Array.Stream
   import: bench-options

core/docs/Changelog.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+### Breaking
+
 * 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
@@ -12,7 +14,25 @@
   default. Literally identical relative paths (e.g. `./x` and `./x`, or
   `c:` and `c:` on Windows) now compare equal. Pass
   `allowRelativeEquality False` to restore the previous strict behaviour.
+
+### Enhancements
+
+* `Streamly.Data.Stream.unfold` no longer requires an `Applicative` constraint
+  and produces a smaller fused loop (one fewer state constructor and Skip on
+  the first pull) for unfolds with a pure inject.
+
+### Bug Fixes
+
 * Bug fix: Fixed `followSymlinks` option not working correctly on macOS.
+* `Streamly.Internal.Data.Unfold.before` previously did not actually run the
+  supplied action due to the wrong `>>` instance being resolved; it now runs
+  as documented.
+
+### Internal
+
+* Unfold constructor's inject changed from monadic to pure. Public APIs
+  unaffected. Direct users of the `Unfold` constructor with a monadic
+  inject should switch to `mkUnfoldM` in `Streamly.Internal.Data.Unfold.Type`.
 
 ## 0.3.0
 

core/src/Streamly/Data/Unfold.hs

@@ -65,9 +65,9 @@ module Streamly.Data.Unfold
     -- ** Mapping on Input
     , lmap
     , lmapM
-    , first
-    , second
-    , carry
+    , supplyFirst
+    , supplySecond
+    , carryInput
 
     -- ** Mapping on Output
     , mapM
@@ -93,6 +93,9 @@ module Streamly.Data.Unfold
 
     -- * Deprecated
     , many
+    , first
+    , second
+    , carry
 
     )
 where

core/src/Streamly/Internal/Data/Array/Type.hs

@@ -1016,7 +1016,7 @@ unsafeReader = Unfold step inject
     where
 
     inject (Array contents start end) =
-        return (MA.ArrayUnsafe contents end start)
+        MA.ArrayUnsafe contents end start
 
     {-# INLINE_LATE step #-}
     step (MA.ArrayUnsafe contents end p) = do

core/src/Streamly/Internal/Data/Fold/Combinators.hs

@@ -2224,7 +2224,7 @@ unfoldMany (Unfold ustep inject) (Fold fstep initial extract final) =
             StreamD.Stop -> return $ Partial fs
 
     {-# INLINE_LATE consume #-}
-    consume s a = inject a >>= produce s
+    consume s a = produce s (inject a)
 
 -- | Get the bottom most @n@ elements using the supplied comparison function.
 --

core/src/Streamly/Internal/Data/MutArray.hs

@@ -97,7 +97,7 @@ indexerFromLen from len =
     let fromThenTo n = (from, from + len, n - 1)
         mkSlice n i = return (i, min len (n - i))
      in Unfold.lmap length
-        $ Unfold.mapM (uncurry mkSlice) . Unfold.carry
+        $ Unfold.mapM (uncurry mkSlice) . Unfold.carryInput
         $ Unfold.lmap fromThenTo Unfold.enumerateFromThenTo
 RENAME(sliceIndexerFromLen,indexerFromLen)
 
@@ -121,7 +121,7 @@ splitterFromLen, slicerFromLen :: forall m a. (Monad m, Unbox a)
 splitterFromLen from len =
     let mkSlice arr (i, n) = return $ unsafeSliceOffLen i n arr
      in Unfold.mapM (uncurry mkSlice)
-        $ Unfold.carry (indexerFromLen from len)
+        $ Unfold.carryInput (indexerFromLen from len)
 RENAME(slicerFromLen,splitterFromLen)
 
 {-# DEPRECATED getSlicesFromLen "Please use splitterFromLen instead." #-}

core/src/Streamly/Internal/Data/MutArray/Type.hs

@@ -1628,7 +1628,7 @@ indexReaderWith liftio (D.Stream stepi sti) = Unfold step inject
     where
 
     inject (MutArray contents start end _) =
-        return $ GetIndicesState contents start end sti
+        GetIndicesState contents start end sti
 
     {-# INLINE_LATE step #-}
     step (GetIndicesState contents start end st) = do
@@ -2215,7 +2215,7 @@ readerRevWith liftio = Unfold step inject
 
     inject (MutArray contents start end _) =
         let p = INDEX_PREV(end,a)
-         in return $ ArrayUnsafe contents start p
+         in ArrayUnsafe contents start p
 
     {-# INLINE_LATE step #-}
     step (ArrayUnsafe _ start p) | p < start = return D.Stop

core/src/Streamly/Internal/Data/Producer.hs

@@ -39,7 +39,7 @@ where
 import Streamly.Internal.Data.Stream.Step (Step(..))
 import Streamly.Internal.Data.Stream.Type (Stream(..))
 import Streamly.Internal.Data.SVar.Type (defState)
-import Streamly.Internal.Data.Unfold.Type (Unfold(..))
+import Streamly.Internal.Data.Unfold.Type (Unfold, mkUnfoldM)
 
 import Streamly.Internal.Data.Producer.Source
 import Streamly.Internal.Data.Producer.Type
@@ -56,8 +56,8 @@ import Prelude hiding (concat)
 --
 -- /Pre-release/
 {-# INLINE simplify #-}
-simplify :: Producer m a b -> Unfold m a b
-simplify (Producer step inject _) = Unfold step inject
+simplify :: Functor m => Producer m a b -> Unfold m a b
+simplify (Producer step inject _) = mkUnfoldM step inject
 
 -------------------------------------------------------------------------------
 -- Unfolds

core/src/Streamly/Internal/Data/RingArray.hs

@@ -465,7 +465,7 @@ reader = Unfold step inject
 
     where
 
-    inject rb = return (rb, ringSize rb)
+    inject rb = (rb, ringSize rb)
 
     step (rb, n) = do
         if n <= 0
@@ -483,7 +483,7 @@ readerRev = Unfold step inject
 
     where
 
-    inject rb = return (moveReverse rb, ringSize rb)
+    inject rb = (moveReverse rb, ringSize rb)
 
     step (rb, n) = do
         if n <= 0

core/src/Streamly/Internal/Data/Scanl/Combinators.hs

@@ -2207,7 +2207,7 @@ unfoldMany (Unfold ustep inject) (Scanl fstep initial extract final) =
             StreamD.Stop -> return $ Partial fs
 
     {-# INLINE_LATE consume #-}
-    consume s a = inject a >>= produce s
+    consume s a = produce s (inject a)
 
 -- | Get the bottom most @n@ elements using the supplied comparison function.
 --