Enhance parallel building (#58)

Move the `keysQueue` implementation out of `Data.PQueue.Internals`.
This allows that module to build in parallel with
`Data.PQueue.Prio.Internals`. It looks like [Cabal can't yet make use of
this](haskell/cabal#976), but work to make
it do so is under way.

Author: treeowl

src/Data/PQueue/Internals.hs

@@ -37,7 +37,6 @@ module Data.PQueue.Internals (
   foldrU,
   foldlU,
 --   traverseU,
-  keysQueue,
   seqSpine,
   unions
   ) where
@@ -48,8 +47,6 @@ import Data.Foldable (foldl')
 import Data.Semigroup (Semigroup(..), stimesMonoid)
 #endif
 
-import qualified Data.PQueue.Prio.Internals as Prio
-
 #ifdef __GLASGOW_HASKELL__
 import Data.Data
 import Text.Read (Lexeme(Ident), lexP, parens, prec,
@@ -690,19 +687,6 @@ seqSpineF Nil z          = z
 seqSpineF (Skip ts') z   = seqSpineF ts' z
 seqSpineF (Cons _ ts') z = seqSpineF ts' z
 
--- | Constructs a priority queue out of the keys of the specified 'Prio.MinPQueue'.
-keysQueue :: Prio.MinPQueue k a -> MinQueue k
-keysQueue Prio.Empty = Empty
-keysQueue (Prio.MinPQ n k _ ts) = MinQueue n k (keysF (const Zero) ts)
-
-keysF :: (pRk k a -> rk k) -> Prio.BinomForest pRk k a -> BinomForest rk k
-keysF f ts0 = case ts0 of
-  Prio.Nil       -> Nil
-  Prio.Skip ts'  -> Skip (keysF f' ts')
-  Prio.Cons (Prio.BinomTree k _ ts) ts'
-    -> Cons (BinomTree k (f ts)) (keysF f' ts')
-  where  f' (Prio.Succ (Prio.BinomTree k _ ts) tss) = Succ (BinomTree k (f ts)) (f tss)
-
 class NFRank rk where
   rnfRk :: NFData a => rk a -> ()
 

src/Data/PQueue/Min.hs

@@ -91,6 +91,7 @@ import Data.Semigroup (Semigroup((<>)))
 import qualified Data.List as List
 
 import Data.PQueue.Internals
+import qualified Data.PQueue.Prio.Internals as Prio
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Exts (build)
@@ -213,3 +214,16 @@ fromDescList xs = foldl' (flip insertMinQ') empty xs
 -- | Equivalent to 'toListU'.
 elemsU :: MinQueue a -> [a]
 elemsU = toListU
+
+-- | Constructs a priority queue out of the keys of the specified 'Prio.MinPQueue'.
+keysQueue :: Prio.MinPQueue k a -> MinQueue k
+keysQueue Prio.Empty = Empty
+keysQueue (Prio.MinPQ n k _ ts) = MinQueue n k (keysF (const Zero) ts)
+
+keysF :: (pRk k a -> rk k) -> Prio.BinomForest pRk k a -> BinomForest rk k
+keysF f ts0 = case ts0 of
+  Prio.Nil       -> Nil
+  Prio.Skip ts'  -> Skip (keysF f' ts')
+  Prio.Cons (Prio.BinomTree k _ ts) ts'
+    -> Cons (BinomTree k (f ts)) (keysF f' ts')
+  where  f' (Prio.Succ (Prio.BinomTree k _ ts) tss) = Succ (BinomTree k (f ts)) (f tss)