Minor bug fixes for yaml-to-dhall error messages

[robbiemcmichael]

Fixes a type mismatch error message which mentions JSON.

---

Fixes an "arithmetic overflow" exception which occurs when attempting to parse a negative number as a Natural.

Current behaviour:

$ yaml-to-dhall Natural <<< -1

arithmetic underflow

With fix applied:

$ yaml-to-dhall Natural <<< -1

Error: Dhall type expression and YAML value do not match:

Expected Dhall type:
Natural

YAML:
-1

[sjakobi]

Nice catch! It would be great to have a regression test for this, but we don't have a test setup for testing errors right now.

Note that this broke the build due to a warning though:

src/Dhall/JSONToDhall.hs:239:1: error: [-Wunused-imports, -Werror=unused-imports]
    The qualified import of ‘Dhall’ is redundant
      except perhaps to import instances from ‘Dhall’
    To import instances alone, use: import Dhall()
    |
239 | import qualified Dhall
    | ^^^^^^^^^^^^^^^^^^^^^^

[Gabriella439]

Also, to fix the build failure, just remove the now-unused import qualified Dhall from the JSONToDhall module:

https://hydra.dhall-lang.org/build/32689/nixlog/4/tail

[robbiemcmichael]

Thanks @sjakobi and @Gabriel439, I've removed the redundant import.

[Gabriella439]

@robbiemcmichael: Thank you for fixing this! 🙂