239cff3 · streamly · git.iko.soy

git.iko.soy/streamly

Add some explanatory notes to Unfold/Fold types.

commit239cff3606375fa5e6057c3917c2ec4e7ca6fde2 authorHarendra Kumar <harendra@composewell.com> dateSun 22 Aug 2021, 04:41 (5 years ago) parentd5a8ebe

2 files changed+8

unifiedsplit

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

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

350350-- The Fold type

351351------------------------------------------------------------------------------

352352

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+

353357-- | The type @Fold m a b@ having constructor @Fold step initial extract@

354358-- represents a fold over an input stream of values of type @a@ to a final

355359-- 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)

8585-- The order of arguments allows 'Category' and 'Arrow' instances but precludes

8686-- contravariant and contra-applicative.

8787--

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+--

8892-- | An @Unfold m a b@ is a generator of a stream of values of type @b@ from a

8993-- seed of type 'a' in 'Monad' @m@.

9094--