Deriving show doesn't parenthesize negative numbers

[arucil]

When I define a data type with an integer member, the show_xx function doesn't add parenthesis around a negative integer member, hence I can't just copy the output and paste into my code to construct an identical value (I use this functionality to write tests).

For example, I wrote

type a = T of int [@@deriving show]

And invoke show_a (T (-20)), the output is (T -20).

By the way, I found Haskell's deriving Show handle negative integers correctly.