Only convert Scientific to Integer for nonnegative exponents

src/Language/GraphQL/Draft/Parser.hs

@@ -33,7 +33,7 @@ import           Data.Attoparsec.Text          (Parser, anyChar, char, many1,
 import qualified Data.Attoparsec.Text          as AT
 import           Data.Char                     (isAsciiLower, isAsciiUpper,
                                                 isDigit)
-import           Data.Scientific               (Scientific)
+import           Data.Scientific               (Scientific, base10Exponent)
 import           Data.Text                     (find)
 
 import qualified Language.GraphQL.Draft.Syntax as AST
@@ -189,8 +189,20 @@ number :: Parser (Either Scientific Integer)
 number = do
   (numText, num) <- match (tok scientific)
   pure $ case Data.Text.find (== '.') numText of
+      -- Number specified with decimals, so store as a 'Scientific'
     Just _ -> Left num
-    Nothing -> Right (floor num)
+      -- Even if there is no '.' in the text, the number may still not
+      -- be integral (e.g. in 3E-7).  Conversely, even a number with a
+      -- negative exponent may still be integral, e.g. 300E-2.  But
+      -- the careful thing to do is to only convert to an 'Integer'
+      -- for numbers with nonnegative exponents.  Note that we can't
+      -- simply delegate this decision to
+      -- 'Data.Scientific.floatingOrInteger' since 'Scientific' does
+      -- not have a 'RealFloat' instance.
+    Nothing ->
+      if base10Exponent num >= 0
+      then Right (floor num)
+      else Left num
 
 -- This will try to pick the first type it can runParser. If you are working with
 -- explicit types use the `typedValue` parser.