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From Kyle Richardson <kylerichards...@gmail.com>
Subject Re: Stellar support for switch/case style conditionals
Date Tue, 24 Oct 2017 15:34:06 GMT
I guess I read it as supporting both. As a user, I certainly would prefer
to use the less explicit syntax ( e.g. match { foo == 0: true, bar == 1:
false, default: false } ).

-Kyle

On Tue, Oct 24, 2017 at 11:30 AM, Casey Stella <cestella@gmail.com> wrote:

> So, I do like it.  My only issue is the explicit lambda syntax in the
> values there (e.g. foo == 0 : () -> true)  I'm afraid that when we migrate
> to a less explicit lambda syntax ( foo == 0 : true ), we will cause people
> to have to transition twice in a row.
>
> Also, it goes without saying, but the syntax must be short-circuiting IMO.
>
> Casey
>
> On Tue, Oct 24, 2017 at 11:26 AM, Kyle Richardson <
> kylerichardson2@gmail.com
> > wrote:
>
> > I like the way you have this laid out. Very useful to see it in test
> cases.
> > I'm +1 for this syntax addition.
> >
> > -Kyle
> >
> > On Mon, Oct 23, 2017 at 4:16 PM, Otto Fowler <ottobackwards@gmail.com>
> > wrote:
> >
> > > What I would like to do for the first PR is introduce match with the
> > > following syntax
> > >
> > >
> > > match{ logical expression   :  transformation expression, ….. ,
> default :
> > > transformation expression}
> > >
> > > Such that the following work  for example:
> > >
> > > @Test
> > > public void testMatch() {
> > >  Assert.assertTrue(runPredicate("match { 1 >= 0 : ()-> true }", new
> > > HashMap(){{
> > >    put("foo", 0);
> > >   }}));
> > >   Assert.assertTrue(runPredicate("match { foo == 0 : ()-> true,
> > > default : ()-> false }", new HashMap(){{
> > >     put("foo", 0);
> > >   }}));
> > >   Assert.assertFalse(runPredicate("match { foo == 0 : ()-> true,
> > > default : ()-> false }", new HashMap(){{
> > >     put("foo", 1);
> > >   }}));
> > >
> > >   Assert.assertTrue(runPredicate("match { foo == 0 : ()-> false, foo
> > > == 1 : ()-> true, default : ()-> false }", new HashMap(){{
> > >     put("foo", 1);
> > >   }}));
> > >
> > >   Assert.assertTrue(runPredicate("match { foo == 0 : ()-> bFalse, foo
> > > == 1 : ()-> bTrue, default : ()-> bFalse }", new HashMap(){{
> > >     put("foo", 1);
> > >     put("bFalse", new Boolean(false));
> > >     put("bTrue", new Boolean(true));
> > >   }}));
> > >
> > >   Assert.assertTrue(runPredicate("match { foo == 0 : ()-> bFalse, foo
> > > == 1 : ()-> bTrue, default : ()-> bFalse }", new HashMap(){{
> > >     put("foo", 1);
> > >     put("bFalse", new Boolean(false));
> > >     put("bTrue", new Boolean(true));
> > >   }}));
> > >
> > >   Assert.assertTrue(runPredicate("match { foo == 0 : bFalse, foo == 1
> > > : bTrue, default : false }", new HashMap(){{
> > >     put("foo", 1);
> > >     put("bFalse", new Boolean(false));
> > >     put("bTrue", new Boolean(true));
> > >   }}));
> > >
> > >   Assert.assertTrue(runPredicate("match { foo == 0  OR bar == 'yes' :
> > > ()-> true, default : ()-> false }", new HashMap(){{
> > >     put("foo", 1);
> > >     put("bar", "yes");
> > >   }}));
> > >
> > >   Assert.assertEquals("warning", run("match{ threat.triage.level < 10
> > > : 'info', threat.triage.level < 20 : 'warning', default : 'critical'
> > > }", new HashMap(){{
> > >     put("threat.triage.level", 15);
> > >   }}));
> > > }
> > >
> > >
> > > So, the transformation expression will include support for zero arg
> > lambda
> > > syntax.  The work to support the AS aliasing statement and lambda
> support
> > > for parameters may page in assignment and some other things,
> > > and I would like to make that a follow on with some discussion after
> > > review.
> > >
> > > Thoughts?
> > >
> > >
> > >
> > > On October 17, 2017 at 14:31:07, Otto Fowler (ottobackwards@gmail.com)
> > > wrote:
> > >
> > > OK
> > >
> > >
> > > On October 17, 2017 at 14:28:02, Casey Stella (cestella@gmail.com)
> > wrote:
> > >
> > > Yeah, default would be a keyword.  We could also do match(variable1 as
> x,
> > > variable2 as y) if you want to alias your fields *or* you could do
> match
> > {
> > > ... } if you dont' want to alias your variables.
> > >
> > > e.g. if you had a field threat.triage.level either of these would work:
> > >
> > > match(threat.triage.level -> x) { x < 10 : 'info', x < 20 : 'warning',
> > > default : 'critical' }
> > > OR
> > > match { threat.triage.level < 10 : 'info', threat.triage.level < 20 :
> > > 'warning, default : 'critical' }
> > >
> > >
> > >
> > > On Tue, Oct 17, 2017 at 2:24 PM, Otto Fowler <ottobackwards@gmail.com>
> > > wrote:
> > >
> > > > No that is it.
> > > >
> > > > So default would be a keyword?
> > > >
> > > > and a lambda that uses x can be used on the right side of the :
> > > >
> > > >
> > > >
> > > > On October 17, 2017 at 14:21:01, Casey Stella (cestella@gmail.com)
> > > wrote:
> > > >
> > > > So, just to map this onto the example, you mean:
> > > > match(longer_variable -> x) { x < 10 : 'info', x <= 20 : 'warn',
> > default:
> > > > 'critical' } ?  I took the liberty of adding a default keyword there
> > the
> > > > evaluation of the conditionals are considered lambda functions also.
> > > >
> > > > Did I catch the spirit of the suggestion or did I miss anything?
> > > >
> > > > On Tue, Oct 17, 2017 at 2:18 PM, Otto Fowler <
> ottobackwards@gmail.com>
> > > > wrote:
> > > >
> > > >> How about this:
> > > >>
> > > >> match(VAR_TO_VAL_ASSIGNMENT+) { BOOLEAN_STATEMENT(VALS) :
> > LAMBDA(VALS),
> > > >> BOOLEAN_STATEMENT(VALS) : LAMBDA(VALS) , LAMBDA(VALS)}
> > > >>
> > > >> * match = new keyword
> > > >> * match takes variable number of assignments, where the val assigned
> > to
> > > >> is available in the evaluation and the lambdas
> > > >> * match {} contains comma separated list of a statement that
> evaluates
> > > to
> > > >> a boolean and a lambda
> > > >> * LAMBDA is executed on match, and it’s value is returned
> > > >> * no matches returns null or return of optional final statement,
> which
> > > is
> > > >> a LAMBDA without a BOOLEAN_STATEMENT
> > > >>
> > > >>
> > > >> On October 17, 2017 at 12:06:05, Casey Stella (cestella@gmail.com)
> > > wrote:
> > > >>
> > > >> Ugh, I forgot to preface this with DISCUSS: Sorry!
> > > >>
> > > >> On Tue, Oct 17, 2017 at 12:05 PM, Casey Stella <cestella@gmail.com>
> > > >> wrote:
> > > >>
> > > >> > Hi All,
> > > >> >
> > > >> > It's high time that Stellar supports some form of conditional
that
> > is
> > > >> > beyond if/then/else. Right now, the way to do fall-through
> > > conditionals
> > > >> is:
> > > >> >
> > > >> > if x < 10 then 'info' else if x >= 10 && x <=
20 then 'warn' else
> > > >> > 'critical'
> > > >> >
> > > >> > That becomes non-scalable very quickly. I wanted to facilitate
a
> > > >> > discussion with the community on the syntax. I'll give a few
> options
> > > and
> > > >> > you guys/gals can come up with your own suggestions too, but
I
> > wanted
> > > to
> > > >> > frame teh conversation.
> > > >> >
> > > >> > *MAP-BASED SWITCH*
> > > >> >
> > > >> > With the advent of METRON-1254 (https://github.com/apache/met
> > > >> ron/pull/801),
> > > >> > we could enable (from a language perspective in Stellar)
> multi-part
> > > >> > conditionals or switch/case style statements. To wit:
> > > >> >
> > > >> > MAP_GET(true, { x < 10 : 'info', x >= 10 && x <=
20 : 'warn', x >
> > 20 :
> > > >> > 'critical' })
> > > >> >
> > > >> > Or, with a convenience function:
> > > >> >
> > > >> > CASE( { x < 10 : 'info', x >= 10 && x <= 20
: 'warn', x > 20 :
> > > >> 'critical'
> > > >> > } )
> > > >> >
> > > >> > The issue with this is that the last true condition wins because
> > we're
> > > >> > using a map.
> > > >> >
> > > >> > *LIST-BASED SWITCH*
> > > >> >
> > > >> > We could correct this by adding a list of pairs construction
to
> > > stellar:
> > > >> >
> > > >> > CASE( [ x < 10 : 'info', x <= 20 : 'warn'], 'critical')
> > > >> >
> > > >> > This would enable us to allow the first true condition to win,
so
> > the
> > > >> > second condition can be simpler and we could pass a default return
> > > >> value as
> > > >> > the final argument.
> > > >> > The downside to this, is that it requires a language enhancement
> > (the
> > > >> list
> > > >> > of pairs construction you see there).
> > > >> >
> > > >> > *LAMBDA FUNCTION-BASED SWITCH*
> > > >> >
> > > >> > Some of the problems with the previous statements are that every
> > > >> > conditional has to be evaluated and there is no opportunity to
> short
> > > >> > circuit. They're all evaluated at parse-time rather than execution
> > > time.
> > > >> > We could, instead, construct a lambda function approach to this
> and
> > > >> support
> > > >> > short-circuiting in even complex conditionals:
> > > >> >
> > > >> > CASE( real_variable_name, [ x -> x < 10 ? 'info', x ->
x <= 20 ?
> > > 'warn'
> > > >> ],
> > > >> > 'critical')
> > > >> > or
> > > >> > CASE( real_variable_name, [ x -> if x < 10 then 'info',
x -> if x
> <=
> > > 20
> > > >> > then 'warn' ], 'critical')
> > > >> >
> > > >> > This would require lessening ?: (if/then/else) syntax to support
> to
> > > >> enable
> > > >> > just if without else conditions. This also has the benefit of
> > allowing
> > > >> > simplifying the expression due to lambda function variable
> renaming
> > > >> > (real_variable_name can be much more complex (or even an
> expression)
> > > >> than
> > > >> > 'x'.
> > > >> >
> > > >> > Creative other approaches to this are appreciated!
> > > >> >
> > > >> > Thanks,
> > > >> >
> > > >> > Casey
> > > >> >
> > > >>
> > > >>
> > > >
> > >
> >
>

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