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src/Language/Haskell/Generate/Monad.hs

@@ -38,16 +38,22 @@ import           Language.Haskell.Generate.Expression
 --------------------------------------------------------------------------------
 -- Generate expressions
 
+-- | This monad keeps track of a counter for generating unique names and the set of modules
+-- that are needed for the expression.
 newtype Generate a = Generate { unGenerate :: StateT Integer (Writer (S.Set ModuleName)) a } deriving (Functor, Applicative, Monad)
 
+-- | Extract the set of modules and the value from a Generate action.
 runGenerate :: Generate a -> (a, S.Set ModuleName)
 runGenerate (Generate a) = runWriter $ evalStateT a 0 
 
+-- | This is a type alias for a Generate action that returns an expression of type 't'.
 type ExpG t = Generate (Expression t)
 
+-- | Use a haskell-src-exts Exp as the result of a Generate action.
 returnE :: Exp -> ExpG t
 returnE = return . Expression
 
+-- | Pretty print the expression generated by a given action.
 generateExp :: ExpG t -> String
 generateExp = prettyPrint . runExpression . fst . runGenerate
 
@@ -88,7 +94,16 @@ newName pref = Generate $ do
   i <- get <* modify succ
   return $ Ident $ pref ++ show i
 
--- | Generate a expression from a haskell value. 
+-- | Generate a expression from a haskell value. This can for example be used to create lambdas:
+-- 
+-- >>> putStrLn $ generateExp $ expr (\x f -> f <>$ x)
+-- \ pvar_0 -> \ pvar_1 -> pvar_1 pvar_0
+--
+-- Or string literals:
+--
+-- >>>  putStrLn $ generateExp $ expr "I'm a string!"
+-- ['I', '\'', 'm', ' ', 'a', ' ', 's', 't', 'r', 'i', 'n', 'g', '!']
+--
 class GenExp t where
   type GenExpType t :: *
 
@@ -129,7 +144,6 @@ instance GenExp x => GenExp (ExpG a -> x) where
 --------------------------------------------------------------------------------
 -- Apply functions
 
-
 -- | Apply a function in a haskell expression to a value.
 applyE :: ExpG (a -> b) -> ExpG a -> ExpG b
 applyE a b = wrap $ liftM (foldl1 App) $ sequence [unwrap a, unwrap b]