error when binding variables

[random-bites]

The Binding section of the Container documentation has the following example.

You can also bind variables to other variables:

my $a = 0;
my $b = 0;
$a := $b;
$b = 42;
say $a; # OUTPUT: «42␤»

However, when I attempt to repeat this example in the rakudo REPL, I get the following error.

my $a = 0;
my $b = 0;
$a := $b;
===SORRY!=== Error while compiling:
Cannot use bind operator with this left-hand side
------> $a := $b;
$b = 42;
42
say $a;
0

Who is right? The documentation or the compiler?

[random-bites]

The binding operator documentation has this example.

my $a = 42;
my $b := $a;
$b++;
say $a;

So, perhaps the variable binding example, in the Container Binding section, should have been written as follows?

my $a = 0;
my $b := $a;
$b = 42;
say $a; # OUTPUT: «42␤»

[JJ]

I'll have to check. This is one of the cases where the REPL might behave in a slightly different way. Thanks anyway for the report.

[random-bites]

Okay, I compiled the following code from a .raku script without errors. Raku and rakudo are new to me, so I didn't realize that there might be different errors when compiling a .raku script vs. using the REPL. Especially, when the code appears so simple.

my $a = 0;
my $b = 0;
$a := $b;
$b = 42;
say $a; # OUTPUT: «42␤»

[JJ]

Any way, we should probably try and use code that works the same in the two places, or simply add a warning. Thanks for the report anyway.

[b2gills]

This is one of the problems with the REPL.

Which is why I often write the entirety of my code on a single line, in an enclosing block

> { my $a = 42; my $b := $a; $b++; say $a; }
43

Another such problem is that operators often don't work correctly either.

> sub postfix:<!> (UInt \n) {[×] 1..n}; say 5!
120
> say 5!
===SORRY!=== Error while compiling:
Negation metaoperator not followed by valid infix
------> say 5!⏏<EOL>
    expecting any of:
        infix
        infix stopper
> 

Every time you press enter it creates a new execution environment. The way it currently does it has its issues.

[coke]

Looking for a place to document the potential issue with the REPL (there isn't really a good one at the moment), I found a footnote here describing a similar problem:

https://docs.raku.org/language/variables#fn-ref-1

I don't think every example that has trouble in the REPL needs a footnote; my recommendation is to add a single warning to the REPL docs.