doesn't compile with ghc 8.2.1

[JakeWheat]

When compiling the latest version on hackage (0.9.22) with ghc 8.2.1, I get the following error:

src/UU/Parsing/Offside.hs:128:9: error:
    • Could not deduce (Position pos)
      from the context: (InputState t1 s p1, Position p1,
                         InputState t1 s1 t0, InputState t1 s pos)
        bound by the inferred type for ‘sameln’:
                   forall pos s1 p1.
                   (InputState t1 s p1, Position p1, InputState t1 s1 t0,
                    InputState t1 s pos) =>
                   t1 -> [a0] -> OffsideInput t1 s t0
        at src/UU/Parsing/Offside.hs:(128,9)-(145,37)
    • In the ambiguity check for the inferred type for ‘sameln’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the inferred type
        sameln :: forall pos s1 p.
                  (InputState t1 s p, Position p, InputState t1 s1 t0,
                   InputState t1 s pos) =>
                  t1 -> [a0] -> OffsideInput t1 s t0
      In an equation for ‘layoutL’:
          layoutL ln ts ms
            | ln /= sln = startln (column pos) ts ms
            | otherwise = sameln ts ms
            where
                sln = line pos
                pos = getPosition ts
                layout = layoutL ln
                implicit = implicitL ln
                ....
    |
128 |         sameln tts ms
    |         ^^^^^^^^^^^^^...

Adding 'AllowAmbiguousTypes' to the language pragma at the top of the file 'src/UU/Parsing/Offside.hs' seems to work, but I have no idea if this is the correct fix.