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 "!ab".
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]" <mlnode+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( GROOVY2576
> <https://issues.apache.org/jira/browse/GROOVY2576> ) .
>
> 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 !ab, 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 !ab 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 !ab, 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 ~ab 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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