Use NonEmpty to clean up errors in integerDec (#655)

Data/ByteString/Builder/ASCII.hs

@@ -85,6 +85,7 @@ import Data.ByteString.Builder.RealFloat (floatDec, doubleDec)
 
 import Foreign
 import Foreign.C.Types
+import Data.List.NonEmpty (NonEmpty(..))
 
 ------------------------------------------------------------------------------
 -- Decimal Encoding
@@ -276,37 +277,31 @@ integerDec i
  | i < 0 = P.primFixed P.char8 '-' `mappend` go (-i)
  | otherwise = go i
  where
- errImpossible fun =
- error $ "integerDec: " ++ fun ++ ": the impossible happened."
-
  go :: Integer -> Builder
  go n | n < maxPow10 = intDec (fromInteger n)
  | otherwise =
  case putH (splitf (maxPow10 * maxPow10) n) of
- (x:xs) -> intDec x `mappend` P.primMapListBounded intDecPadded xs
- [] -> errImpossible "integerDec: go"
+ x:|xs -> intDec x `mappend` P.primMapListBounded intDecPadded xs
 
- splitf :: Integer -> Integer -> [Integer]
+ splitf :: Integer -> Integer -> NonEmpty Integer
  splitf pow10 n0
- | pow10 > n0 = [n0]
+ | pow10 > n0 = n0 :| []
  | otherwise = splith (splitf (pow10 * pow10) n0)
  where
- splith [] = errImpossible "splith"
- splith (n:ns) =
+ splith (n:|ns) =
  case n `quotRem` pow10 of
- (q,r) | q > 0 -> q : r : splitb ns
- | otherwise -> r : splitb ns
+ (q,r) | q > 0 -> q :| r :  splitb ns
+ | otherwise ->  r :| splitb ns
 
  splitb [] = []
  splitb (n:ns) = case n `quotRem` pow10 of
  (q,r) -> q : r : splitb ns
 
- putH :: [Integer] -> [Int]
- putH [] = errImpossible "putH"
- putH (n:ns) = case n `quotRem` maxPow10 of
+ putH :: NonEmpty Integer -> NonEmpty Int
+ putH (n:|ns) = case n `quotRem` maxPow10 of
  (x,y)
- | q > 0 -> q : r : putB ns
- | otherwise -> r : putB ns
+ | q > 0 -> q :| r :  putB ns
+ | otherwise ->  r :| putB ns
  where q = fromInteger x
  r = fromInteger y