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MyASPN >> Mail Archive >> perl6-language
perl6-language
Re: return() in pointy blocks
by =22TSa_=28Thomas_Sandla=DF=29=22 other posts by this author
Jun 8 2005 1:57AM messages near this date
Re: return() in pointy blocks | Re: return() in pointy blocks
Luke Palmer wrote:
>  Says not:
>  
>     Boo
>     Boo
>     Boo
>     ...

This is clear, but I would expect the output

    Boo
    42

because the return value of foo is a ref to a block that
makes the caller return 42. This is written in my current
Perl6 as

&foo:( : -->  Block --> 42)

The question is when exactly this call chain is invoked:

   1) when it is assigned to $code? Or,
   2) when &postfix:<( )>  is invoked on $code?

I prefer 2) because it better fits my understanding of
referential semantics. About the relationship to the lazy
versus eager trade-off I'm unsure. So 1) is also a good
choice.

With this in mind, I wonder how \ and ->  are related. Is

   $x = 3;
   $rw = ->  $x;

valid syntax? And does it mean that

   $rw = 7;
   say $x; # prints 7

This can be construed as the eager version of

   $x = 3;
   $rw = ->  { $x };

   $rw = 7;
   say $x; # means: say $x();

A block in a chain of references is a stop mark in a chain of refs.

   $x  = 3;
   $r  = ->  $x;
   $rr = ->  $r;

   say $rr();  # prints 3, because say $r; also prints 3

   $rr = 7;
   say $r;  # prints 7
   say $x;  # prints 3

Looks like we have found a candidate for the transparent ref creator!
And I hope Juerd likes it. After all it looks *pointy* :)

PS: A chain of refs can thus be reduced to the leaf lvalue with
     ([()] $rr) = 23; which stores a new value in $x. This might even
     warrant the special case of ([] $rr) = 23;
-- 
TSa (Thomas Sandlaß)
Thread:
Ingo Blechschmidt
Matt Fowles
Luke Palmer
=22TSa_=28Thomas_Sandla=DF=29=22
=22TSa_=28Thomas_Sandla=DF=29=22
Larry Wall
"TSa (Thomas Sandlaß)"
Larry Wall
Matt Fowles

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