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From Daniel Sun <realblue...@hotmail.com>
Subject 答复: 答复: About the "implies" operator(GROOVY-2576)
Date Thu, 26 Jan 2017 10:01:15 GMT
Hi Guillaume,

      When we deal with logic, abstraction is very important to simplify reasoning. The “implies”
operator can give us a hand here 😊

Cheers,
Daniel.Sun

发件人: Guillaume Laforge [via Groovy]<mailto:ml-node+s329449n5738107h75@n5.nabble.com>
发送时间: 2017年1月26日 17:34
收件人: Daniel Sun<mailto:realbluesun@hotmail.com>
主题: Re: 答复: About the "implies" operator(GROOVY-2576)

I'm not super convinced either, and I'm wondering when I'd really use such an operator.
I'm kinda +0 as Cédric here.

Not that we should copy or not other languages, but are there others that have such an operator,
and if this is the case, do we know how (much) it's used?

On Thu, Jan 26, 2017 at 10:22 AM, Cédric Champeau <[hidden email]</user/SendEmail.jtp?type=node&node=5738107&i=0>>
wrote:
I know it's well known in mathematical logic, but I don't want Groovy to become Scalaz either.
The route is dangerous.

2017-01-26 10:18 GMT+01:00 Daniel Sun <[hidden email]</user/SendEmail.jtp?type=node&node=5738107&i=1>>:
Hi Cédric,

     Here is the background of the “implies” operator, which is well known in the mathematical
logic 😉
http://mathworld.wolfram.com/Implies.html


发件人: [hidden email]<http:///user/SendEmail.jtp?type=node&node=5738105&i=0>
发送时间: 2017年1月26日 17:12
收件人: [hidden email]<http:///user/SendEmail.jtp?type=node&node=5738105&i=1>
主题: Re: About the "implies" operator(GROOVY-2576)

I'm not convinced we should add more operators. Honestly, I had to read the description of
the "implies" operator to understand what it does. This is clearly not the case for || or
&&, which are "well known" operators.

I am also worried about code becoming ascii art:

{ a -> a => a <= c => d }

So I'm just +0, I don't see that I would use it often enough to mitigate the drawbacks.

2017-01-26 1:47 GMT+01:00 Daniel Sun <[hidden email]<http:///user/SendEmail.jtp?type=node&node=5738104&i=0>>:
Hi Jochen,

      Thanks for your analysis in detail :)

       => is a very expressive operator. if we could implement it as +(corresponding to
plus method) does and apply different business logic when necessary, it would be much more
useful. And the default implementation of "implies" method can be "!a||b".

        As to the association of the operator, I prefer the left association, i.e. a =>
b => c is equivalent to (a => b) => c.

       The above is the initial plan to implement the  "implies" operator.

Cheers,
Daniel.Sun


在 2017年1月26日 上午3:20,"Jochen Theodorou [via Groovy]" <ml-node+s329449n5738042h6
On 25.01.2017 17:50, Daniel Sun wrote:

> Hi all,
>
>        The "implies" operator "=>" was suggested many years ago, here is the
> replated JIRA issue( GROOVY-2576
> <https://issues.apache.org/jira/browse/GROOVY-2576>  ) .
>
>        Do you want it for Groovy 3? (+1: yes; -1: no; 0: not bad)
>
>        BTW, recently I have been going through the issues related to the old
> parser, many issues existing for many years do not exist in the new parser
> Parrot :)

If we do this (and I say +1) we should clear some things:
1) what does a=>b=>c mean, since (a=>b)=>c is not the same as a=>(b=>c)
2) use groovy truth and when to apply it? If we map a=>b to !a||b, then
it will use Groovy truth on a and b, but if we map to an implies method
it will get a and b, use groovy truth on them or not and we then maybe
use groovy truth on the result. I personally would be for not using
groovy truth here, thus make it more in line with | and &.
3) if a=>b is mapped to !a||b we will evaluate a, negate it, and
depending on the result maybe never evaluate b. As long as a and b are
free of side effects, that does not play an extremely important role,
but if we map it to a method a and b will be evaluated always. If we
would say it is more like !a|b, which would also require both being
evaluated, then there is still the fact that !a ensures we call here
always the boolean or function, never one defined by an arbitrary a
4) instead of using !a, which converts a to a boolean and negates it, we
can also use ~a, which is a binary negate also working on booleans, but
not converting a to a boolean if it is no boolean. Here we have to
especially think about ~a|b calling "or" on a Pattern if a is a String.
Also not many things besides boolean and numbers really support
something useful of the binary negate.

I mention those points so we can make a proper specification for the
behaviour of this operator ;)

bye Jochen


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Developer Advocate @ Google Cloud Platform

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