Add support for infix applications

This was released on hackage in version 0.1.0.3 by accident.

It's fairly simplistic; effects are sequenced operator-left-right,
somewhat arbitrarily.

Control/Applicative/QQ/Idiom.hs

@@ -4,7 +4,8 @@
 
 module Control.Applicative.QQ.Idiom (i) where
 
-import Control.Applicative
+import Control.Applicative ((<*>), pure)
+import Control.Monad ((<=<))
 import Language.Haskell.Meta (parseExp)
 import Language.Haskell.TH.Lib
 import Language.Haskell.TH.Quote
@@ -13,18 +14,12 @@ import Language.Haskell.TH.Syntax
 -- ghci> [$i| (,) "foo" "bar" |]
 -- [('f','b'),('f','a'),('f','r'),('o','b'),('o','a'),('o','r'),('o','b'),('o','a'),('o','r')]
 i :: QuasiQuoter
-i = QuasiQuoter { quoteExp = applicateQ }
+i = QuasiQuoter { quoteExp = applicate <=< either fail return . parseExp }
 
-applicateQ :: String -> ExpQ
-applicateQ s = case either fail unwindE (parseExp s) of
-                  x:y:xs -> foldl
-                              (\e e' -> [|$e <*> $e'|])
-                              [|$(return x) <$> $(return y)|]
-                              (fmap return xs)
-                  _ -> fail "applicateQ fails."
-
-unwindE :: Exp -> [Exp]
-unwindE = go []
-  where go acc (e `AppE` e') = go (e':acc) e
-        go acc e = e:acc
+applicate :: Exp -> ExpQ
+applicate (AppE f x) =
+  [| $(applicate f) <*> $(return x) |]
+applicate (InfixE (Just left) op (Just right)) =
+  [| pure $(return op) <*> $(return left) <*> $(return right) |]
+applicate x = [| pure $(return x) |]