$ cabal get optparse-generic
Downloading optparse-generic-1.3.0...
Unpacking to optparse-generic-1.3.0/
$ cd optparse-generic-1.3.0/
$ cabal new-build -w ~/src/ghc-hh-8.6/inplace/bin/ghc-stage2
$ ~/src/ghc-hh-8.6/inplace/bin/ghc-stage2 --interactive
GHCi, version 8.5.20180530: http://www.haskell.org/ghc/  :? for help
Loaded package environment from
/home/simon/tmp/tmp2/optparse-generic-1.3.0/.ghc.environment.x86_64-linux-8.5.20180530
Loaded GHCi configuration from /home/simon/.ghci
λ :load src/Options/Generic.hs
[1 of 1] Compiling Options.Generic  ( src/Options/Generic.hs, interpreted )
Ok, one module loaded.
λ :doc getRecord
ghc-stage2: Can't find any documentation for Options.Generic.
This is probably because the module was loaded without '-haddock',
but it's also possible that the module contains no documentation.

Try running ':set -haddock' and :load the file again.
λ :set -haddock
λ :load src/Options/Generic.hs
[1 of 1] Compiling Options.Generic  ( src/Options/Generic.hs, interpreted )
Ok, one module loaded.
λ :doc getRecord
 Marshal any value that implements `ParseRecord` from the command line

 If you need to modify the top-level 'ParserInfo' or 'ParserPrefs'
 use the 'getRecordWith' function.
λ :doc Only
ghc-stage2: Can't find any documentation for Data.Tuple.Only.
This is probably because the module was compiled without '-haddock',
but it's also possible that the module contains no documentation.

Try re-compiling with '-haddock'.
λ
Leaving GHCi.
$ cabal new-build -w ~/src/ghc-hh-8.6/inplace/bin/ghc-stage2
--ghc-options "-haddock"
$ ~/src/ghc-hh-8.6/inplace/bin/ghc-stage2 --interactive
GHCi, version 8.5.20180530: http://www.haskell.org/ghc/  :? for help
Loaded package environment from
/home/simon/tmp/tmp2/optparse-generic-1.3.0/.ghc.environment.x86_64-linux-8.5.20180530
Loaded GHCi configuration from /home/simon/.ghci
λ :load src/Options/Generic.hs
[1 of 1] Compiling Options.Generic  ( src/Options/Generic.hs, interpreted )
Ok, one module loaded.
λ :doc Only
<has no documentation>

 The 1-tuple type or single-value "collection".

 This type is structurally equivalent to the
 'Data.Functor.Identity.Identity' type, but its intent is more
 about serving as the anonymous 1-tuple type missing from Haskell for attaching
 typeclass instances.

 Parameter usage example:

 @encodeSomething ('Only' (42::Int))@

 Result usage example:

 @xs <- decodeSomething
forM_ xs $ \\('Only' id) -> {- ... -}@

λ :doc x

<interactive>:1:1: error: Not in scope: ‘x’
λ x = ()
λ :doc x
Docs are unavailable for interactive declarations.
λ :doc Monad
 The 'Monad' class defines the basic operations over a /monad/,
a concept from a branch of mathematics known as /category theory/.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an /abstract datatype/ of actions.
Haskell's @do@ expressions provide a convenient syntax for writing
monadic expressions.

Instances of 'Monad' should satisfy the following laws:

* @'return' a '>>=' k  =  k a@
* @m '>>=' 'return'  =  m@
* @m '>>=' (\\x -> k x '>>=' h)  =  (m '>>=' k) '>>=' h@

Furthermore, the 'Monad' and 'Applicative' operations should relate as follows:

* @'pure' = 'return'@
* @('<*>') = 'ap'@

The above laws imply:

* @'fmap' f xs  =  xs '>>=' 'return' . f@
* @('>>') = ('*>')@

and that 'pure' and ('<*>') satisfy the applicative functor laws.

The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
defined in the "Prelude" satisfy these laws.