From 98329e0a3dd4f78b5d815ac3896272ec70904901 Mon Sep 17 00:00:00 2001 From: Eugen Wissner Date: Thu, 11 Dec 2025 10:28:11 +0100 Subject: Add remaining haskell book exercises --- Haskell-book/26/Embedded/src/OuterInner.hs | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) create mode 100644 Haskell-book/26/Embedded/src/OuterInner.hs (limited to 'Haskell-book/26/Embedded/src') diff --git a/Haskell-book/26/Embedded/src/OuterInner.hs b/Haskell-book/26/Embedded/src/OuterInner.hs new file mode 100644 index 0000000..edc31c1 --- /dev/null +++ b/Haskell-book/26/Embedded/src/OuterInner.hs @@ -0,0 +1,30 @@ +module OuterInner where + +import Control.Monad.Trans.Except +import Control.Monad.Trans.Maybe +import Control.Monad.Trans.Reader + +-- We only need to use return once +-- because it's one big Monad +embedded :: MaybeT + (ExceptT String + (ReaderT () IO)) + Int +--embedded = return 1 +embedded = MaybeT . ExceptT . ReaderT $ return . (const (Right (Just 1))) + +-- We can sort of peel away the layers one by one: +maybeUnwrap :: ExceptT String + (ReaderT () IO) (Maybe Int) +maybeUnwrap = runMaybeT embedded + +-- Next +eitherUnwrap :: ReaderT () IO + (Either String (Maybe Int)) +eitherUnwrap = runExceptT maybeUnwrap + +-- Lastly +readerUnwrap :: () + -> IO (Either String + (Maybe Int)) +readerUnwrap = runReaderT eitherUnwrap \ No newline at end of file -- cgit v1.2.3