foldMap package:streamly-core

Definition:

>>> foldMap f = Fold.lmap f Fold.mconcat

Make a fold from a pure function that folds the output of the function using mappend and mempty.

>>> sum = Fold.foldMap Data.Monoid.Sum

>>> Stream.fold sum $ Stream.enumerateFromTo 1 10
Sum {getSum = 55}

Definition:

>>> foldMap f = Scanl.lmap f Scanl.mconcat

Make a scan from a pure function that scans the output of the function using mappend and mempty.

>>> sum = Scanl.foldMap Data.Monoid.Sum

>>> Stream.toList $ Stream.scanl sum $ Stream.enumerateFromTo 1 3
[Sum {getSum = 0},Sum {getSum = 1},Sum {getSum = 3},Sum {getSum = 6}]

Definition:

>>> foldMapM f = Fold.lmapM f Fold.mconcat

Make a fold from a monadic function that folds the output of the function using mappend and mempty.

>>> sum = Fold.foldMapM (return . Data.Monoid.Sum)

>>> Stream.fold sum $ Stream.enumerateFromTo 1 10
Sum {getSum = 55}

Definition:

>>> foldMapM f = Scanl.lmapM f Scanl.mconcat

Make a scan from a monadic function that scans the output of the function using mappend and mempty.

>>> sum = Scanl.foldMapM (return . Data.Monoid.Sum)

>>> Stream.toList $ Stream.scanl sum $ Stream.enumerateFromTo 1 3
[Sum {getSum = 0},Sum {getSum = 1},Sum {getSum = 3},Sum {getSum = 6}]