Skip to content

Add MonadFix instance for Codensity #74

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
finnteegen wants to merge 1 commit into
base: master
Choose a base branch
from
Open

Add MonadFix instance for Codensity #74

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 4 additions & 0 deletions src/Control/Monad/Codensity.hs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@ module Control.Monad.Codensity
import Control.Applicative
import Control.Monad (MonadPlus(..))
import qualified Control.Monad.Fail as Fail
import Control.Monad.Fix
import Control.Monad.Free
import Control.Monad.IO.Class
import Control.Monad.Reader.Class
Expand Down Expand Up @@ -168,6 +169,9 @@ instance MonadPlus v => MonadPlus (Codensity v) where
{-# INLINE mplus #-}
#endif

instance MonadFix v => MonadFix (Codensity v) where
mfix f = Codensity (\k -> mfix (lowerCodensity . f) >>= k)

-- |
-- This serves as the *left*-inverse (retraction) of 'lift'.
--
Expand Down