Add native arithmetical expressions support

[Hywan]

A trivial merge of Hoa\Math in this library to get native arithmetical expressions support.

It will introduce a change (so a break) in the grammar. Array declarations will be [1, 2, 3] and no longer (1, 2, 3). The library has the RC state, so we can still introduce BC breaks. I particulary ask @stephpy, @shouze and @osaris to get their feedbacks :-).

Note: we should not add new features in the grammar in the future. If we want more power, we should focus on Hoathis\Lua which is a much better scripting language (imperative, procedural, functional etc.).

[stephpy]

I don't understand, you want to merge ruler and math grammar to support thinkgs like (2 + user.nb_vote) > context.minimum_vote_to_win ?

[Hywan]

“merge” is not really appropriated. I just would like to see the same features, i.e. native arithmetical expressions. And to reply to your question: yes :-).

[stephpy]

Ok, that would be a good point. But is “Ruler“ a good name ? May be it would be appropriated to make something more global like symfony\ExpressionLanguage ?

[Hywan]

No, as I said, if we need more features, we should focus on Lua which is a real scripting language (more powerful than Symfony\ExpressionLanguage). But are arithmetical operations a need in rules? That's the real question I think.

[shouze]

@Hywan I think that Ruler should stay a Rete rule algorithm like lib. I'm not very confortable with the fact you can assign a value to any variable in this lib. Should be immutable & read only system I think.

[Hywan]

@shouze Oh sure, it will be immutable. I propose the support of arithmetical expression, not assignation. The example of @stephpy is right: user.nb_vote + 2 > context.minimum_vote_to_win / 2 for example.

(thanks for the link)

[shouze]

ok, so I'm fully ok with that 👍

[Hywan]

Actually, it will not be so much difficult (I think). Arithmetical operators will be introduce in the grammar and treated as Hoa\Ruler\Model\Operator. Maybe we will need some tricks for the minus operator bu we will see. Anyone interesting for a PR?

[Hywan]

But what about the BC break it will introduce?

[stephpy]

Why (1,2,3) could not be supported ? The SQL like syntax of rule is interesting, if we can keep it, it would be better.

[stephpy]

Oh, due to conflicts with arythmetic operations (x + y) etc...

If we can't support it, let's go for []

[Hywan]

(7) is an array or just 7 ;-) ? This is ambiguous.