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## Re: Combining multiple "is..." traits into one?

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From:
yary
Date:
August 12, 2020 05:05
Subject:
Re: Combining multiple "is..." traits into one?
Message ID:
CAG2CFAaxZ1Zd8PKRuKhjCUif0RjZgj-vVirfYvRk5eYQ_ADCuw@mail.gmail.com
```I played with the "is" trait and I is puzzled. This example code

multi trait_mod:<is> (Routine \routine, :\$equality!) {
trait_mod:<is>(routine, :equiv(&infix:<==>));
}

sub is-eq is equality { ... }
say 'is-eq      ', &is-eq.prec;

multi trait_mod:<is> (Routine \routine, :\$chainable!) {
trait_mod:<is>(routine, :assoc<chain>);
}

sub chained is chainable { ... }
say 'chained    ', &chained.prec;

multi trait_mod:<is> (Routine \routine, :\$equivalence!) {
trait_mod:<is>(routine,:equality);
trait_mod:<is>(routine,:chainable);
}

# Uncomment these two lines
# sub trait-er is equality is chainable { ... }
# say 'trait-er   ', &trait-er.prec;

# or uncomment these two lines
# sub jolly-trait is equivalence { ... }
# say 'jolly-trait',&jolly-trait.prec;

run it as-is, and the results make sense to me
is-eq      {iffy => 1, pasttype => chain, prec => m=}
chained    {assoc => chain}

if I uncomment either of the two-line stanzas at the end, the output of
is-eq also changes.

is-eq      {*assoc => chain*, iffy => 1, pasttype => chain, prec => m=}
chained    {assoc => chain}
trait-er   {assoc => chain, iffy => 1, pasttype => chain, prec => m=}

is-eq      {*assoc => chain*, iffy => 1, pasttype => chain, prec => m=}
chained    {assoc => chain}
jolly-trait{assoc => chain, iffy => 1, pasttype => chain, prec => m=}

What is going on, why are the traits changing for 'is-eq' in the
uncommented examples?

-y

On Tue, Aug 11, 2020 at 5:38 PM Stuart Hungerford <
stuart.hungerford@gmail.com> wrote:

> On Wed, Aug 12, 2020 at 8:12 AM Tobias Boege <tobs@taboege.de> wrote:
>
> > [...]
> > > Would a custom version of the trait_mod:<is> routine do the trick?
> >
> > Yes:
> >
> >   multi trait_mod:<is> (Routine \$r, :\$equivalence!) {
> >       trait_mod:<is>(\$r, :equiv(&infix:<==>));
> >       trait_mod:<is>(\$r, :assoc<chain>);
> >   }
>
> As a supplementary question: is it possible to build up trait
> modifications from simpler ones? Something like:
>
> multi trait_mod:<is> (Routine \routine, :\$equality!) {
>   trait_mod:<is>(routine, :equiv(&infix:<==>));
> }
>
> multi trait_mod:<is> (Routine \routine, :\$chainable!) {
>   trait_mod:<is>(routine, :assoc<chain>);
> }
>
> multi trait_mod:<is> (Routine \routine, :\$equivalence!) {
>   {magic to ensure routine is equality and routine is chainable}
> }
>
> Although I'm not yet sure that's a good idea.
>
> Thanks,
>
> Stu
>

```
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