From c1b7f370daece2016a325d9439275140c6325874 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Nowak?= <pawel834@gmail.com>
Date: Thu, 30 Oct 2014 16:36:55 +0100
Subject: [PATCH] Add proper parsing of applications (using a bifold!).

---
 Main.hs              | 13 +++++++++----
 syntax-example.cabal |  4 ++--
 test.txt             |  2 ++
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/Main.hs b/Main.hs
index 6b2ed72..b014e4d 100644
--- a/Main.hs
+++ b/Main.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 
 import           Control.Applicative
+import           Control.Lens.SemiIso
 import           Control.Lens.TH
 import qualified Data.Attoparsec.Text as AP
 import           Data.Char
@@ -11,6 +12,7 @@ import           Data.Syntax (Syntax)
 import qualified Data.Syntax as S
 import qualified Data.Syntax.Attoparsec.Text as S
 import qualified Data.Syntax.Char as S
+import qualified Data.Syntax.Combinator as S
 import qualified Data.Syntax.Pretty as S
 import           Data.Text (Text)
 import qualified Data.Text.IO as T
@@ -37,14 +39,17 @@ atom :: Syntax syn Text => syn AST
 atom =  _Var /$/ name
     /|/ parens expr
 
+-- | Parsers a list of applications.
+apps :: Syntax syn Text => syn AST
+apps = bifoldl1 (attemptAp_ _App) /$/ S.sepBy1 atom S.spaces1
+
 -- | An expression of our lambda calculus.
 expr :: Syntax syn Text => syn AST
-expr =  _App /$/ atom /* S.spaces1 /*/ atom
-    /|/ _Abs /$/ S.char '\\'   /* S.spaces_
+expr =  _Abs /$/ S.char '\\'   /* S.spaces_
               */ name          /* S.spaces
              /*  S.string "->" /* S.spaces
-             /*/ expr 
-    /|/ atom
+             /*/ expr
+    /|/ apps
 
 main :: IO ()
 main = do
diff --git a/syntax-example.cabal b/syntax-example.cabal
index edbe482..122f966 100644
--- a/syntax-example.cabal
+++ b/syntax-example.cabal
@@ -16,7 +16,7 @@ source-repository head
 
 executable syntax-example
   main-is:             Main.hs
-  build-depends:       base >= 4 && < 5, lens, semi-iso,
-                       syntax, syntax-attoparsec, syntax-pretty,
+  build-depends:       base >= 4 && < 5, lens, semi-iso >= 0.3,
+                       syntax >= 0.1.1, syntax-attoparsec, syntax-pretty,
                        attoparsec, pretty, text
   default-language:    Haskell2010
diff --git a/test.txt b/test.txt
index 7cf178a..8014942 100644
--- a/test.txt
+++ b/test.txt
@@ -3,3 +3,5 @@
       -> f     (x x)) (\x 
 -> f  (x x)
 )
+(\x -> x)
+(\y -> y y)