Fix parser swallowing whitespace in Src annotations

[EggBaconAndSpam]

The parser annotated application expressions incorrectly: whitespace
between function and argument was swallowed when constructing the Src
annotation. This bug resulted in strange behaviour in the hovering
functionality in dhall-lsp-server.

As an example, previously the Dhall expression 0 0 would be parsed as

Note (Src {..., srcText = "00"})
     (App (Note (Src {..., srcText = "0"}) (NaturalLit 0))
          (Note (Src {..., srcText = "0"}) (NaturalLit 0)))

while we now get

Note (Src {..., srcText = "0 0"})
     (App (Note (Src {..., srcText = "0"}) (NaturalLit 0))
          (Note (Src {..., srcText = "0"}) (NaturalLit 0)))

as expected.

[sjakobi]

Note that there are quite a few more
occurences of foldl where we don't actually need laziness, but I leave
that for someone else to fix :)

Can you make an issue so we don't forget about it?

[EggBaconAndSpam]

Good point ;)

[EggBaconAndSpam]

I made a separate pull request for using foldl' everywhere.

[sjakobi]

Maybe we should come up with a way to test the Notes that we parse directly: Find out what properties dhall-lsp-server relies on and try to put them into property tests…

[sjakobi]

| otherwise would work too, but it doesn't matter a lot.

[EggBaconAndSpam]

Maybe we should come up with a way to test the Notes that we parse directly: Find out what properties dhall-lsp-server relies on and try to put them into property tests…

Feel free! I don't think this is as trivial as one would hope, since we really want to test all Notes inside a parsed expression; the top-level parser wraps everything in a Note anyway, so just looking at the outermost Note wouldn't be too useful.

The only way I see to go about this is to construct a 'concatenative' pretty-printer and to compare the Notes inside a parsed, pretty-printed expression against the result of pretty-printing the sub-expressions. The problem is that our pretty-printer isn't concatenative...