From fea361cfbb6d1409d31f612a816030216c05b516 Mon Sep 17 00:00:00 2001
From: Martijn van Steenbergen <martijn@van.steenbergen.nl>
Date: Wed, 30 Nov 2011 00:35:43 +0100
Subject: [PATCH 1/2] Explicit type signature for `c` in function `derive`.
 Fixes https://github.com/sebastiaanvisser/fclabels/issues/4

---
 src/Data/Label/Derive.hs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Data/Label/Derive.hs b/src/Data/Label/Derive.hs
index 8330d55..7a12644 100644
--- a/src/Data/Label/Derive.hs
+++ b/src/Data/Label/Derive.hs
@@ -5,6 +5,7 @@
   , FlexibleContexts
   , FlexibleInstances
   , TypeOperators
+  , RankNTypes
   #-}
 module Data.Label.Derive
 ( mkLabels
@@ -101,7 +102,7 @@ derive signatures concrete tyname vars total ((field, _, fieldtyp), ctors) =
       where
         mono = forallT prettyVars (return []) [t| $(inputType) :~> $(return prettyFieldtyp) |]
         poly = forallT forallVars (return []) [t| (ArrowChoice $(arrow), ArrowZero $(arrow)) => Lens $(arrow) $(inputType) $(return prettyFieldtyp) |]
-        body = [| let c = zeroArrow ||| returnA in lens (c . $(getter)) (c . $(setter)) |]
+        body = [| let c :: forall b d (~>). Either b d ~> d; c = zeroArrow ||| returnA in lens (c . $(getter)) (c . $(setter)) |]
           where
             getter    = [| arr (\    p  -> $(caseE [|p|] (cases (bodyG [|p|]      ) ++ wild))) |]
             setter    = [| arr (\(v, p) -> $(caseE [|p|] (cases (bodyS [|p|] [|v|]) ++ wild))) |]

From 5533d3bcfa754560080624bfe3b0ca605b5448dc Mon Sep 17 00:00:00 2001
From: Martijn van Steenbergen <martijn@van.steenbergen.nl>
Date: Wed, 30 Nov 2011 00:44:44 +0100
Subject: [PATCH 2/2] Fix for more complicated cases

---
 src/Data/Label/Derive.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Data/Label/Derive.hs b/src/Data/Label/Derive.hs
index 7a12644..145e408 100644
--- a/src/Data/Label/Derive.hs
+++ b/src/Data/Label/Derive.hs
@@ -102,7 +102,7 @@ derive signatures concrete tyname vars total ((field, _, fieldtyp), ctors) =
       where
         mono = forallT prettyVars (return []) [t| $(inputType) :~> $(return prettyFieldtyp) |]
         poly = forallT forallVars (return []) [t| (ArrowChoice $(arrow), ArrowZero $(arrow)) => Lens $(arrow) $(inputType) $(return prettyFieldtyp) |]
-        body = [| let c :: forall b d (~>). Either b d ~> d; c = zeroArrow ||| returnA in lens (c . $(getter)) (c . $(setter)) |]
+        body = [| let c :: forall b d (~>). (ArrowChoice (~>), ArrowZero (~>)) => Either b d ~> d; c = zeroArrow ||| returnA in lens (c . $(getter)) (c . $(setter)) |]
           where
             getter    = [| arr (\    p  -> $(caseE [|p|] (cases (bodyG [|p|]      ) ++ wild))) |]
             setter    = [| arr (\(v, p) -> $(caseE [|p|] (cases (bodyS [|p|] [|v|]) ++ wild))) |]