Rewrite CPSy code as do-code using QualifiedDoqualified-contdo

Credits for this trick go to Leary on IRC:
https://ircbrowse.tomsmeding.com/browse/lchaskell?id=1691743#trid1691743

Advantage: all the binders are on the left-hand side.
Disadvantages:
- all continuations need to pass exactly one value, i.e. tuples are
  required
- wacky shit

1 files changed, 15 insertions, 0 deletions

diff --git a/src/ContDo.hs b/src/ContDo.hs
new file mode 100644
index 0000000..255e21a
--- /dev/null
+++ b/src/ContDo.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MonoLocalBinds #-}
+module ContDo where
+
+import GHC.TypeLits
+
+(>>=) :: (a -> b) -> a -> b
+(>>=) = ($)
+
+class AlwaysFail a
+instance TypeError (Text "fail") => AlwaysFail a
+
+fail :: AlwaysFail a => String -> a
+fail = error