239cff3 · streamly · git.iko.soy

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Add some explanatory notes to Unfold/Fold types.

239cff3Harendra Kumar5 years ago

src/Streamly/Internal/Data/Fold/Type.hs+4

@@ -350,6 +350,10 @@ mapMStep f res =

350-- The Fold type

351------------------------------------------------------------------------------

352

353+-- An fold is akin to a writer. It is the streaming equivalent of a writer.

354+-- The type @b@ is the accumulator of the writer. That's the reason the

355+-- default folds in various modules are called "write".

356+

353-- | The type @Fold m a b@ having constructor @Fold step initial extract@

357-- | The type @Fold m a b@ having constructor @Fold step initial extract@

354-- represents a fold over an input stream of values of type @a@ to a final

358-- represents a fold over an input stream of values of type @a@ to a final

355-- value of type @b@ in 'Monad' @m@.

359-- value of type @b@ in 'Monad' @m@.

src/Streamly/Internal/Data/Unfold/Type.hs+4

@@ -85,6 +85,10 @@ import Prelude hiding (map, concatMap, zipWith, takeWhile)

85-- The order of arguments allows 'Category' and 'Arrow' instances but precludes

86-- contravariant and contra-applicative.

87--

88+-- An unfold is akin to a reader. It is the streaming equivalent of a reader.

89+-- The argument @a@ is the environment of the reader. That's the reason the

90+-- default unfolds in various modules are called "read".

91+--

88-- | An @Unfold m a b@ is a generator of a stream of values of type @b@ from a

92-- | An @Unfold m a b@ is a generator of a stream of values of type @b@ from a

89-- seed of type 'a' in 'Monad' @m@.

93-- seed of type 'a' in 'Monad' @m@.

90--

94--