Proposal: better negation syntax

[yrashk]

So, right now the syntax is really awkwardly hard:

-neg_rule({determine_engine_state, [{'working-state', engine, '__IGNORE_UNDERSCORE__'},
                                    {repair, '__IGNORE_UNDERSCORE__'}]}).
%% ...
determine_engine_state(Engine, {start, _})
  when not {rule, [{'working-state', engine, _}, {repair, _}]} ->

I was just thinking, and basing on my experience writing Exportie (https://github.com/spawngrid/exportie) I am pretty sure we can pack this above example to:

determine_engine_state(Engine,{start,_},not([{'working-state', engine, _}, {repair, _}]) ->
...

I am not sure I can use not there, but if I can't, we can't settle with another keyword, such as negative or unless

If you agree with this proposal I will implement this and send a pull request. Please let me know.

[ericbmerritt]

This seems reasonable to me. and its more inline with the direction I am thinking of going with the API rewrite. The only possible concern I have is making sure the negative is visible. however, I suspect its ok.

[yrashk]

Alright. I will implement this additional rewrite then.

[yrashk]

I am no longer sure this is a good idea. I mean, overall, it does seem to be interesting, but it will obscure rule's actual arity

[yrashk]

I guess what confuses me in the existing syntax is this {rule, []}

What we can do (at least) is to get rid of the list, and if somebody wants to match multiple not-rules, they should do when not {rule, A} andalso not {rule, B} kind of thing.

Also, since we're controlling the parse transformation in question, may be we can make this look this way: not rule(A)? I am pretty sure I can do that with applications on forms level. I do the same thing to function arguments in exportie.

[ericbmerritt]

I am ok with that I suspect.

[yrashk]

good, will try playing with this whenever I'll get around that.