From 565236d0577a55af9dfd546e444d7bc5424827d1 Mon Sep 17 00:00:00 2001
From: Ryan Scott <ryan.gl.scott@gmail.com>
Date: Tue, 28 Nov 2023 07:59:03 -0500
Subject: [PATCH] Add Data instances for BigFloat, Sign, BFRep, BFNum

Fixes #28.
---
 CHANGELOG.md          |  4 ++++
 src/LibBF.hs          | 10 ++++++++++
 src/LibBF/Mutable.hsc |  8 +++++---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b53fffb..0ff92fa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Revision history for libBF-hs
 
+## next -- TBA
+
+* Add `Data` instances for `BigFloat`, `Sign`, `BFRep`, and `BFNum`.
+
 ## 0.6.6 -- 2023.07.17
 
 * Update the vendored version of `libbf` to include the changes from the
diff --git a/src/LibBF.hs b/src/LibBF.hs
index b2a1022..3ace56e 100644
--- a/src/LibBF.hs
+++ b/src/LibBF.hs
@@ -61,6 +61,7 @@ module LibBF
 
 
 import Data.Bits
+import Data.Data (Data(..))
 import Data.Hashable
 import Data.Word
 import Data.Int
@@ -73,6 +74,15 @@ import Control.DeepSeq
 -- | Arbitrary precision floating point numbers.
 newtype BigFloat = BigFloat BF
 
+instance Data BigFloat where
+  -- BigFloat is exported as an abstract data type, so we intentionally define
+  -- the Data instance in a simplistic way so as to avoid leaking the BF
+  -- internals.
+  gfoldl _ z = z
+  gunfold _ _ = error "Data.Data.gunfold(BigFloat)"
+  toConstr _ = error "Data.Data.toConstr(BigFloat)"
+  dataTypeOf _ = error "Data.Data.dataTypeOf(BigFloat)"
+
 instance NFData BigFloat where
   rnf x = x `seq` ()
 
diff --git a/src/LibBF/Mutable.hsc b/src/LibBF/Mutable.hsc
index 50e6cb9..f9810d8 100644
--- a/src/LibBF/Mutable.hsc
+++ b/src/LibBF/Mutable.hsc
@@ -2,6 +2,7 @@
 {-# Language PatternSynonyms #-}
 {-# Language MultiWayIf #-}
 {-# Language BlockArguments #-}
+{-# Language DeriveDataTypeable #-}
 -- | Mutable big-float computation.
 module LibBF.Mutable
   ( -- * Allocation
@@ -69,6 +70,7 @@ import Foreign.Ptr(Ptr,FunPtr,minusPtr)
 import Foreign.ForeignPtr
 import Foreign.C.Types
 import Foreign.C.String
+import Data.Data (Data)
 import Data.Word
 import Data.Int
 import Data.Bits
@@ -175,7 +177,7 @@ bf3 f (BF fin1) (BF fin2) (BF fout) =
 
 -- | Indicates if a number is positive or negative.
 data Sign = Neg {-^ Negative -} | Pos {-^ Positive -}
-             deriving (Eq,Ord,Show)
+             deriving (Data,Eq,Ord,Show)
 
 
 foreign import ccall "bf_set_nan"
@@ -553,7 +555,7 @@ toString radix (ShowFmt ds flags) =
 -- | An explicit representation for big nums.
 data BFRep  = BFRep !Sign !BFNum    -- ^ A signed number
             | BFNaN                 -- ^ Not a number
-              deriving (Eq,Ord,Show)
+              deriving (Data,Eq,Ord,Show)
 
 instance Hashable BFRep where
   hashWithSalt s BFNaN           = s `hashWithSalt` (0::Int)
@@ -564,7 +566,7 @@ instance Hashable BFRep where
 data BFNum  = Zero                 -- ^ zero
             | Num Integer !Int64   -- ^ @x * 2 ^ y@
             | Inf                  -- ^ infinity
-              deriving (Eq,Ord,Show)
+              deriving (Data,Eq,Ord,Show)
 
 instance Hashable BFNum where
   hashWithSalt s Zero         = s `hashWithSalt` (0::Int)