Special case for 'build' on minBound of Integral types. Fixes #18

Data/Text/Buildable.hs

@@ -25,7 +25,7 @@ import Data.Int (Int8, Int16, Int32, Int64)
 import Data.Fixed (Fixed, HasResolution, showFixed)
 import Data.Ratio (Ratio, denominator, numerator)
 import Data.Text.Format.Functions ((<>))
-import Data.Text.Format.Int (decimal, hexadecimal)
+import Data.Text.Format.Int (decimal, hexadecimal, integer)
 import Data.Text.Format.Types (Hex(..), Shown(..))
 import Data.Text.Lazy.Builder
 import Data.Time.Calendar (Day, showGregorian)
@@ -91,7 +91,7 @@ instance Buildable Int64 where
     {-# INLINE build #-}
 
 instance Buildable Integer where
-    build = decimal
+    build = integer 10
     {-# INLINE build #-}
 
 instance (HasResolution a) => Buildable (Fixed a) where

Data/Text/Format/Int.hs

@@ -12,6 +12,7 @@
 module Data.Text.Format.Int
     (
       decimal
+    , integer
     , hexadecimal
     , minus
     ) where
@@ -39,7 +40,7 @@ import GHC.Integer.GMP.Internals
 # define PAIR(a,b) (a,b)
 #endif
 
-decimal :: Integral a => a -> Builder
+decimal :: (Bounded a, Integral a)=> a -> Builder
 {-# SPECIALIZE decimal :: Int -> Builder #-}
 {-# SPECIALIZE decimal :: Int8 -> Builder #-}
 {-# SPECIALIZE decimal :: Int16 -> Builder #-}
@@ -52,6 +53,10 @@ decimal :: Integral a => a -> Builder
 {-# SPECIALIZE decimal :: Word64 -> Builder #-}
 {-# RULES "decimal/Integer" decimal = integer 10 :: Integer -> Builder #-}
 decimal i
+    | i == minBound =
+        -- special case, since (-i) would not be representable assuming two's
+        -- compliment:
+        minus <> integer 10 (negate $ fromIntegral i)
     | i < 0     = minus <> go (-i)
     | otherwise = go i
   where

text-format.cabal

@@ -1,5 +1,5 @@
 name:           text-format
-version:        0.3.1.1
+version:        0.3.1.2
 license:        BSD3
 license-file:   LICENSE
 homepage:       https://github.com/bos/text-format