diff --git a/manuscript/backmatter.md b/manuscript/backmatter.md
index be994f30..64acedfd 100644
--- a/manuscript/backmatter.md
+++ b/manuscript/backmatter.md
@@ -634,6 +634,14 @@ explicitly, which is more boilerplate but makes the code easier to read:
                                      println line
 ~~~~~~~~
 
+Whereas in Scala this encoding may be called *Finally Tagless*, in Haskell it is
+known as MTL style. Without going into details, some Scala developers didn't
+understand a research paper about the performance benefits of [Generalised ADTs
+in Haskell](http://okmij.org/ftp/tagless-final/index.html#tagless-final).
+
+An alternative to MTL style are *Extensible Effects*, also known as [Free Monad
+style](http://okmij.org/ftp/Haskell/extensible/more.pdf).
+
 
 ## Modules
 
diff --git a/manuscript/book.org b/manuscript/book.org
index eebb6966..1020b09d 100644
--- a/manuscript/book.org
+++ b/manuscript/book.org
@@ -17026,6 +17026,14 @@ echo Console{readln, println} = do line <- readln
                                    println line
 #+END_SRC
 
+Whereas in Scala this encoding may be called /Finally Tagless/, in Haskell it is
+known as MTL style. Without going into details, some Scala developers didn't
+understand a research paper about the performance benefits of [[http://okmij.org/ftp/tagless-final/index.html#tagless-final][Generalised ADTs
+in Haskell]].
+
+An alternative to MTL style are /Extensible Effects/, also known as [[http://okmij.org/ftp/Haskell/extensible/more.pdf][Free Monad
+style]].
+
 *** Modules
 
 Haskell source code is arranged into hierarchical modules with the restriction