[WIP] Adding Position Annotation

[zhujinxuan]

There will be a big change if we want to add position annotation as discussed in #75

We used to have schema :: a -> AST, then it will be schema :: a -> (Int, Int) -> AST

[zhujinxuan]

Sees that the coverage test fails because we do not test `position` in record explicitly. I am not sure whether we need to test this?

Update: Commit from d004986 the coverage test with ticks overlay.

[teh]

Quick question: Under what circumstances would position be Nothing? Would it make sense to add a brief comment about that?

[zhujinxuan]

Annotation added in 0023709. Nothing will be used for manually constructed ASTs. For example, when a client manually construct AST and encode the AST to query (for sending to server). When constructing the AST, the position information is missing.

[teh]

What does this do? Is it this https://wiki.haskell.org/Haskell_program_coverage?

[zhujinxuan]

Yes, it is an overlay of hpc. I did it because position is not intended to be tested as function. (Haskell will translate records@{position = x}torecords _ x`, and therefore is not considered tested in HPC)

One method is to add one in hpc python script, but I think it makes more sense to use a ticks file to explicitly tell those functions we do not need to test.

[zhujinxuan]

Close this PR because adding position directly to AST is not a good idea. I am checking about Free or CoFree to describe the position-annotated parser. (https://www.reddit.com/r/haskell/comments/4x22f9/labelling_ast_nodes_with_locations/)