💡 Dream API for error reporting (2022/7/28 draft)

[favonia]

Changes:

• merge info and warning into print

Based on the Discord discussion:

E.tracef ?loc "when@ loading@ module@ %s" name @@ fun () -> ...
;;
E.printf ~code:`GalaxyNumber ?loc "number@ %i@ is@ too@ large" very_small_number
;;
E.fatalf ~code:`TypeError ?loc "%a@ does@ not@ have@ type@ %a" pp_tm tm pp_ty ty
;;
E.printf ~code:`EmojiError ?loc ~marks:all_occurrences
  "emoji@ %a@ is@ used@ more@ than@ %i@ times."
  pp_emoji emoji threshold
;;
E.messagef ~code:`TypeError ?loc
  "%s@ has@ type@ type@ %a,@ but@ we@ expected@ it@ to@ have@ type@ %a."
  var pp_tp actual pp_tp expected
|> E.mark [binding_loc1; binding_loc2]
|> E.fatal
;;
E.messagef ?loc ~code:`ChiError "variable@ name@ %s@ does@ not@ have@ any@ emojis." var
|> E.fatal ~marks:[]
;;
E.printf ?loc ~code:`ChiInfo "raise@ %s@ here." "CCHM"

In sum, we should have these functions

1. (repeated) tracef to construct a backtrace
2. messagef to construct a message
3. mark to add, well, marks
4. fatal(f) and print(f) to log something, and all four variants can take ?marks
5. fatal(f) intends to end the program after printing out the message.
6. The -f functions always take ?loc.
7. No significance of the ordering of marks (via ?marks and/or calls of E.mark).

[favonia]

Further notes on location inheritance: no inheritance except for the LSP protocol.

[favonia]

Note: we need to decide what location (or none) to use when loc is omitted.