feat(pp): pretty print implementation draft

[lushoBarlett]

Compiles without warnings for now...

I will draft this because I need some suggestions:

1. Should I do the "missing case" bit? I don't think its necessary.
2. How can I test this? (where should I wire the pretty_print function?
3. What behavior is expected of this function regarding "width"?

Closes #136.

[SebastianMestre]

should be inside namespace CST to match with the definition in pretty_print.cpp

[SebastianMestre]

Looks like you implemented pretty-printing over std::ostream, so I would expose the slightly more efficient pretty_print(Cst&, ostream&) (while also keeping the string-returning pretty_print(Cst&) for convenience)

[SebastianMestre]

1. Should I do the "missing case" bit? I don't think its necessary.

I think assert() would be fine

2. How can I test this?

Round-tripping between pretty-printing and parsing (CST -> text -> same CST) is a good way to gain confidence in the printer, but it might be kind of arduous to write.

I'll be pragmatic and say that checking some specific input-output (cst, text) pairs is good enough. We can add regression tests if we find any bugs.

(where should I wire the pretty_print function?

I think we could use it in the playground executable. Also very low priority, so feel free to ignore/do in a separate PR.

• 3. What behavior is expected of this function regarding "width"?

You mean limiting the number of columns per line of code? It's famously pretty difficult. There is a famous paper by Philip Wadler outlining a pretty decent and simple approach.

Tbh I am happy with the printer in this PR (no column limit), but if you want to add that, a separate PR would be welcome.

[SebastianMestre]

Suggested change

	#include <sstream>
	#include "log/log.hpp"
	#include "pretty_print.hpp"
	#include "pretty_print.hpp"
	#include "log/log.hpp"
	#include <sstream>

as a general rule I try to always include the .hpp corresponding to the current .cpp as the first line

Also, stdlib includes after project includes

[SebastianMestre]

There are some minor style thingies but generally LGTM -- feel free to merge when you're happy with it