Parsing errors location not helpful

[zmrocze]

Hey,

over the past few days with dhall oftentimes I encountered parsing errors with the error location very distant to the fix location. The debugging often gave me good few minutes of "find elmo" fun.

The location and description of parsing errors often seems in human terms unrelated to the error.

Below one such minimal unparsing example. Will add more. The parsing error occurs here at the m letter in map = with description: "expecting whitespace or }".

{ profiles.mk2_3by4 = {
  setting_note_0vel_is_noteoff = True,
  map =
    let config =
      ({
        intervals =
          let mkIntervals = \({ pressed_channel : Integer, played_channel : Integer  }) -> 
            lib.list-map Integer (lib.Pair lib.Note { intervals : List lib.Note})
              (\(i : Integer) -> { 
                key = { note = lib.int-add +60 i, channel = pressed_channel },
                val = { intervals = [ { note = i, channel = played_channel } ] }
              })
              (lib.range { from = -9, to = +4 })
          in
            [
              (mkIntervals { pressed_channel = +0, played_channel = +0 }),
              (mkIntervals { pressed_channel = +1, played_channel = +1 })
            ]
      })
    in lib.by_intervals config
  },
}

The error "really" happens in the definition of mkIntervals where the lambda lacks its argument name, there's only the argument type.

Another example is where usage of : instead of = in record values results in errors somewhere else completely.

[Gabriella439]

This is more of an issue with the Haskell implementation, so I'll move this to the Haskell repository's issue tracker

[Gabriella439]

Yeah, the Dhall parser has a few known issues with error reporting. Probably the most central issue relevant to this is: #1592

Basically, fixing this properly requires a bit of an overhaul to the parser