derived-instances.md

@@ -14,12 +14,13 @@ Automatic derivation of instances is jolly useful.  Current problems are:
   ```
 
   as an example.
-- Even in the absence of user-defined deriving, it should be easy for a 'newtype' decl to inherit some of the instances of its parent type, no matter where the class was defined, but this is currently only available as a ghc extension to haskell'98.
+- Even in the absence of user-defined deriving, it should be easy for a `newtype` declaration to inherit some of the instances of its parent type, no matter where the class was defined, but this is currently only available as a GHC extension to Haskell 98 (see [NewtypeDeriving](newtype-deriving)).
 
+## User-specified derived instances
 
-There are various extant proposals to enable the user-specification of the derivation of class instances.
 
-- [NewtypeDeriving](newtype-deriving)
+There are various extant proposals to enable the user-specification of the derivation of class instances:
+
 - PolyP ([ Jeuring and Jansson](http://www.cs.uu.nl/~johanj/publications/notes.ps), AFP 1996)
 - ghc -fgenerics (Hinze, [ PoPL 2000](http://www.informatik.uni-bonn.de/~ralf/publications/POPL00.ps.gz), [ Haskell Workshop 1999](http://www.informatik.uni-bonn.de/~ralf/publications/HW99.ps.gz), [ Haskell Workshop 2000](http://www.informatik.uni-bonn.de/~ralf/publications/HW00.ps.gz))
 - Lightweight Generics ([ Cheney and Hinze](http://www.informatik.uni-bonn.de/~ralf/publications/HW2002.pdf), Haskell Workshop 2002)
@@ -30,3 +31,15 @@ There are various extant proposals to enable the user-specification of the deriv
 - external tools: [ DrIFT](http://repetae.net/~john/computer/haskell/DrIFT/), [ Strafunski](http://www.cs.vu.nl/Strafunski/)
 - [ Generic Haskell](http://www.generic-haskell.org/) preprocessor
 - fill out this list with some more…?
+
+## Standalone derived instances
+
+
+The development version of GHC adds a top-level declaration on the form:
+
+```wiki
+'deriving' qtycls 'for' qtycon
+```
+
+
+which produces the same instance as would be produced by a `deriving` clause in a `data` or `newtype` declaration, but allows this derivation to be decoupled from the datatype declaration, e.g. in another module.