Re: **@args question

2019-01-03 Thread Brad Gilbert
On Thu, Jan 3, 2019 at 12:43 AM ToddAndMargo via perl6-users
 wrote:
>
> On 1/2/19 10:17 PM, ToddAndMargo via perl6-users wrote:
> >  > On Wed, Jan 2, 2019 at 8:41 PM ToddAndMargo via perl6-users
> >  >  wrote:
> >  >>
> >  >> Hi All,
> >  >>
> >  >> Looking at
> >  >>
> >  >>  https://docs.perl6.org/routine/print
> >  >>
> >  >> I see
> >  >>
> >  >>  multi sub print(**@args --> True)
> >  >>
> >  >> Question.  If I wanted to create my own print routine
> >  >> using **@args, how would I declare it?
> >  >>
> >  >>  sub printx( **@args data ) {...}
> >  >>
> >  >>
> >  >> Many thanks,
> >  >> -T
> >
> >
> > On 1/2/19 10:06 PM, Brad Gilbert wrote:
> >> The variable name in :(**@args) is @args, it could be any valid array
> >> identifier like @data
> >>
> >>  sub printx( **@data ){…}
> >>
> >> Note that there are several forms for slurpy positional arguments.
> >>
> >>  :(   @a ) # not slurpy at all, takes one Positional argument and
> >> aliases it as @a.
> >>
> >>  :(  *@a ) # flattening slurpy  (1,),2,3 → 1,2,3 and ((1,),2,3) →
> >> 1,2,3
> >>  :( **@a ) # structured slurpy (1,),2,3 → (1,),2,3 and ((1,),2,3) →
> >> ((1,),2,3) # note there is no change
> >>  :(  +@a ) # one-arg rule slurpy (1,),2,3 → (1,),2,3 and ((1,),2,3)
> >> → (1,),2,3 # note that the second one changes
> >>
> >> Note that itemized values do not get flattened for :(*@a), and that
> >> Array values are itemized.
> >>
> >> I like to consider the one-arg rule slurpy :(+@a) to be like a
> >> combination between non-slurpy :(@a) and structured slurpy :(**@a)
> >> That is a one-arg rule slurpy will sometimes be like an alias to a
> >> singular positional, otherwise it will act like a structured slurpy.
> >>
> >> Note that all but the [aliasing] non-slurpy :(@a) are [almost] always
> >> Array's.
> >>
> >> ---
> >>
> >> The one-arg rule slurpy is the oddest one of the bunch so here is some
> >> brief information:
> >>
> >> The one-arg rule slurpy can be sigiless :(+a), in which case it will
> >> be a List instead of an Array or an alias to the single argument
> >> depending on what it was.
> >>
> >>  sub one-arg-rule ( +args ){
> >>  say args.^name, " # ", args.perl;
> >>  }
> >>
> >>  one-arg-rule(  (1,),2,3  ); # List # ((1,), 2, 3)
> >>  one-arg-rule( ((1,),2,3) ); # List # ((1,), 2, 3) # one-arg rule
> >>  one-arg-rule( ((1,),2,3).Seq ); # Seq # ((1,), 2, 3).Seq #
> >> one-arg rule
> >>  one-arg-rule(  1..3   ); # List # (1, 2, 3)
> >>  one-arg-rule( (1..3,) ); # List # (1..3,)
> >>
> >>  sub one-arg-Array ( +@args ){
> >>  say @args.^name, " # ", @args.perl;
> >>  }
> >>
> >>  one-arg-Array(  (1,),2,3  ); # Array # [(1,), 2, 3]
> >>  one-arg-Array( ((1,),2,3) ); # Array # [(1,), 2, 3]
> >>  one-arg-Array( ((1,),2,3).Seq ); # List # ((1,), 2, 3)
> >>  one-arg-Array(  1..3   ); # Array # [1, 2, 3]
> >>  one-arg-Array( (1..3,) ); # Array # [1..3,]
> >>
> >> The one-arg rule exists because people tend to write the following:
> >>
> >>  my @a = [1,2,3];
> >>
> >> When the correct way to write it is:
> >>
> >>  my @a = 1,2,3;
> >>
> >> There are various other places where the one-arg rule is also used, so
> >> it was made available to everyone.
> >>
> >> ---
> >>
> >> Don't get too flustered if you don't understand all of the nuances, it
> >> take everybody a while to understand them.
> >>
> >
> > Thank you!
> >
> > The term "slurpy" did help a lot.
> >
> > :-)
> >
> > I am writing your explanation down for my records.
>
>
> Well Golly!
>
> $ p6 'sub printx(**@args){print(@args)}; printx("abc",1,"def\n");'
> abc 1 def
>
> $ p6 'sub printx(**@args){print @args, "\n"}; printx("abc",1,"def");'
> abc 1 def
>
> Question:
> $ p6 'sub printx(**@args){print(@args)}; printx("abc","xyz","def\n");'
> abc xyz def
>
> Are the spaces suppose to be there?

The spaces are there because you are passing `@args` to `print` as a
single value.
`print` coerces all its values to `Str` before printing, and an Array
adds spaces between elements when turned into a Str.

Simple fix use `|@args` to Slip it into the call to `print`

$ p6 'sub printx(**@args){print( |@args, "\n" )};
printx("abc","xyz","def");'
abcxyzdef


Re: **@args question

2019-01-03 Thread Richard Hainsworth




The term "slurpy" did help a lot.

:-)

I am writing your explanation down for my records.



Well Golly!

$ p6 'sub printx(**@args){print(@args)}; printx("abc",1,"def\n");'
abc 1 def

$ p6 'sub printx(**@args){print @args, "\n"}; printx("abc",1,"def");'
abc 1 def

Question:
$ p6 'sub printx(**@args){print(@args)}; printx("abc","xyz","def\n");'
abc xyz def

Are the spaces suppose to be there?


In each case you are using 'print @args', then `printx` adds on a "\n" 
either to the last item or the final string, which in each case results 
in exactly the same string. The way 'print' handles an array is to put a 
space between each item, which can be very confusing when dealing with 
items that are themselves strings with spaces.


For other "stringifications" of an array, try 'print @args.fmt("%s,")' 
if you want a comma, or 'print @args.perl'.


I find '.say for @args' is better because I get an item on each line.

Also 'dd @args' is quite useful.