deferred-folds 0.4 → 0.4.0.1

raw patch · 2 files changed

+22/−2 lines, 2 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• deferred-folds.cabal +1/−1
• library/DeferredFolds/Unfold.hs +21/−1

@@ -1,7 +1,7 @@ name:   deferred-folds version:-  0.4+  0.4.0.1 category:   Folding synopsis:

@@ -34,8 +34,28 @@  Then we get to this simple morphism: ->foldl' :: [a] -> Unfold a+>list :: [a] -> Unfold a+>list list = Unfold (\ step init -> foldl' step init list) +We can do the same with say "Data.Text.Text":++>text :: Text -> Unfold Char+>text text = Unfold (\ step init -> Data.Text.foldl' step init text)++And then we can use those both to concatenate with just an @O(1)@ cost:++>abcdef :: Unfold Char+>abcdef = list ['a', 'b', 'c'] <> text "def"++Please notice that up until this moment no actual data materialization has happened and+hence no traversals have appeared.+All that we've done is just composed a function,+which only specifies which parts of data structures to traverse to perform a left-fold.+Only at the moment where the actual folding will happen will we actually traverse the source data.+E.g., using the "fold" function:++>abcdefLength :: Int+>abcdefLength = fold Control.Foldl.length abcdef -} newtype Unfold input =   Unfold (forall output. (output -> input -> output) -> output -> output)