Erlang's Maps:to_json Not Found

I have been wanting to learn Erlang for quite some time, and last spring I bought the book Programming Erlang: Software for a Concurrent World to begin that journey. I read about 70% of the book and then life handed me some curve balls that suspended this great journey until recently. I rebooted my learning with Erlang by going through the book and doing the exercises at the end of each chapter. (Bonus: those exercises are under git if you are interested programming_erlang .) All was fine until I got to chapter five and learned of this disconnect…

Joe Armstrong describes three BIFs, “built in function”, that ship with R17 of Erlang to convert JSON to maps

  • maps:to_json(Map) -> Bin
  • maps:from_json(Bin) -> Map
  • maps:safe_from_json(Bin) -> Map

Delving into that module from erl tells a different tale unfortunately…

R17 Maps method list
maps:module_info(exports).

% [{get,3},

%  {fold,3},

%  {map,2},

%  {size,1},

%  {without,2},

%  {with,2},

%  {module_info,0},

%  {module_info,1},

%  {values,1},

%  {update,3},

%  {remove,2},

%  {put,3},

%  {new,0},

%  {merge,2},

%  {keys,1},

%  {is_key,2},

%  {from_list,1},

%  {get,2},

%  {find,2},

%  {to_list,1}]

So, what gives?? Why the missing json methods? A bit of googling and you’ll find this:

I have not read Joes final book on the matter (several drafts though) .. and I’ve told him, twice I think, that there will not be any maps to json BIFs to in the maps module. It does not belong in the standard library.

Björn-Egil

This Bjorn seems like quite the hard-ass, with the power to lay down ultimate authority on these maters. Just who does he think he is?!?! Well it turns out he’s a dude who knows what he’s talking about. After a bit more digging into the issue it turns out that turning JSON into Erlang is not a strait solution. The keys can be represented in serveral different ways and there are already libraries out in the wild handling them in different ways.

TL;DR;

How do you want your keys? <<"key">>, [107,101,121], or key ? Rather than impose a single standard pick a library that works the way you need and expect it to.

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