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: Cédric Champeau [via
Groovy]<mailto:[email protected]>
发送时间: 2017年1月26日 17:12
收件人: Daniel Sun<mailto:[email protected]>
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]</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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