Haskell: add --positions=range flag to include start and end position

[Commelina]

Fixes #461 .

This PR added a --positions=range flag to the --haskell backend. The flag generates AST nodes with both start and end position:

type BNFC'Position = C.Maybe ((C.Int, C.Int), (C.Int, C.Int))

The position is also stored in generated Agda AST. However, it is currently not supported for layout grammars (the end position is always the same as the start one).

There should be absolutely NO change on ANY generated file if --positions=range is not given.

Some snippets from #463 are used.

TODO:

1. Code cleanup (especially these with functor, withEndPos, hasFunctorOption, etc.)
2. Detailed docs
3. Add basic unit tests for --functor-v2
4. Add end-to-end tests to ensure the generated files are not changed without the new flag (maybe build an old version and compare, anyway there should be a framework for such kind of tests)
5. Support layout grammars

Item 1 and 2 are necessary before this PR can be merged.

[andreasabel]

How about organizing the option name like this: --positions=range|start|line. (Alternative for range: span but it seems that "range" is the more modern terminology.)

Legacy	Meaning
--line-numbers	--positions=line
--functor	--positions=start

--posititions=range is the new one (this PR).

Defaults if just --positions is passed:

• Haskell: range
• C/C++/Java the current only option: line

Internally:

data Positions
  = None
  | Range
  | Start
  | Line

[Commelina]

Finished the first step unifying the position-related options, and --positions=start|range should work as expected for the Haskell backend (--functor is an alias to --positions=start now). line is present only internally.

[andreasabel]

Thanks!

I tried this on one example for Haskell and Agda, and found no issues.

[fizruk]

So cool to have this merged! Thanks for picking this up @Commelina!