This program
my #bitfields;
for ^3 -> $i {
#bitfields[$i] = Bool.pick xx 3;
}
my #total = 0 xx 3;
for #bitfields -> #row {
#total Z+= #row;
}
say #total;
says [0 0 0]. If we add something to the loop, whatever:
my #bitfields;
for ^3 -> $i {
#bitfields[$i] = Bool.pick xx 3;
}
my #total = 0 xx 3;
for #bitfields -> #row {
#total Z+= #row;
say "foo";
}
say #total;
It will work correctly. Apparently, the last element of the block is thrown into sink context which in this case means it's simply ignored; this trap is related to that. However, that code above looks perfectly fine; and this
{#total Z+= #^þ} for #bitfields;
apparently works, although I don't see the real difference. Any other idea?
It looks like a bug to me.
This looks very closely related to Which context confuses this Perl 6 zip operator? which became a Rakudo repo issue Failure to sink for when Z+= used as last statement which was closed with roast tests Test sunk for sinks last statement sub calls .
The mystery is why there's a new bug. My suspicion is that someone needs to clean the kitchen sink, i.e. pick up where Zoffix left off with his Flaws in implied sinkage / &unwanted helper issue.
Here's my best golf shot so far for narrowing down the new problem or regression:
my $foo = 'a';
ok: for 1 { $foo X= 'b' }
notok: for 1 -> $_ { $foo X= 'c' }
say $foo; # b
halfok: 'd' ~ do for 1 -> $_ { $foo X= 'e' } # Useless use of "~"
say $foo; # e
The ok: line works because it omits the -> argument.
The notok: line is my golf of your problem.
The error message for the halfok: line is because the result of it is thrown away. But the do has forced the compiler to evaluate the $foo X= 'e' expression in the block, as it should, and as it had failed to in the notok: line.
{#total Z+= #^þ} for #bitfields;
Perhaps that's because that's the non-modifier version. And/or because it doesn't use the -> syntax (which is part of the regression or new bug per my golf above).
Or perhaps just luck. I think most of the sink handling code in Rakudo is Larry's work from long ago when he was trying to get things mostly working right.
Related
I was looking at REPL-like evaluation of code from here and here, and tried to make a very small version for it, yet it fails:
use nqp;
class E {
has Mu $.compiler;
has $!save_ctx;
method evaluate(#fragments) {
for #fragments -> $code {
my $*MAIN_CTX;
my $*CTXSAVE := self;
$!compiler.eval($code,
outer_ctx => nqp::ctxcaller(nqp::ctx()));
if nqp::defined($*MAIN_CTX) {
$!save_ctx := $*MAIN_CTX;
}
}
}
method ctxsave(--> Nil) {
say "*in ctxsave*";
$*MAIN_CTX := nqp::ctxcaller(nqp::ctx());
$*CTXSAVE := 0;
}
}
my $e := E.new(compiler => nqp::getcomp("Raku"));
nqp::bindattr($e, E, '$!save_ctx', nqp::ctx());
$e.evaluate: ('say my #vals = 12, 3, 4;', 'say #vals.head');
I pieced together this from the above links without very much knowing what I'm doing :) When run, this happens:
*in ctxsave*
[12 3 4]
===SORRY!=== Error while compiling file.raku
Variable '#vals' is not declared. Did you mean '&val'?
file.raku:1
------> say ⏏#vals.head
with Rakudo v2022.04. First fragment was supposed to declare it (and prints it). Is it possible to do something like this, so it recognizes #vals as declared?
You can do it in pure Raku code, although depending on the not-exactly-official context parameter to EVAL.
# Let us use EVAL with user input
use MONKEY;
loop {
# The context starts out with a fresh environment
state $*REPL-CONTEXT = UNIT::;
# Get the next line of code to run.
my $next-code = prompt '> ';
# Evaluate it; note that exceptions with line numbers will be
# off by one, so may need fixups.
EVAL "\q'$*REPL-CONTEXT = ::;'\n$next-code", context => $*REPL-CONTEXT;
}
Trying it out:
$ raku simple-repl.raku
> my $x = 35;
> say $x;
35
> my $y = 7;
> say $x + $y;
42
In Ruby I can group together some lines of code like so with a begin block:
x = begin
puts "Hi!"
a = 2
b = 3
a + b
end
puts x # 5
it's immediately evaluated and its value is the last value of the block (a + b here) (Javascripters do a similar thing with IIFEs)
What are the ways to do this in Raku? Is there anything smoother than:
my $x = ({
say "Hi!";
my $a = 2;
my $b = 3;
$a + $b;
})();
say $x; # 5
Insert a do in front of the block. This tells Raku to:
Immediately do whatever follows the do on its right hand side;
Return the value to the do's left hand side:
my $x = do {
put "Hi!";
my $a = 2;
my $b = 3;
$a + $b;
}
That said, one rarely needs to use do.
Instead, there are many other IIFE forms in Raku that just work naturally without fuss. I'll mention just two because they're used extensively in Raku code:
with whatever { .foo } else { .bar }
You might think I'm being silly, but those are two IIFEs. They form lexical scopes, have parameter lists, bind from arguments, the works. Loads of Raku constructs work like that.
In the above case where I haven't written an explicit parameter list, this isn't obvious. The fact that .foo is called on whatever if whatever is defined, and .bar is called on it if it isn't, is both implicit and due to the particular IIFE calling behavior of with.
See also if, while, given, and many, many more.
What's going on becomes more obvious if you introduce an explicit parameter list with ->:
for whatever -> $a, $b { say $a + $b }
That iterates whatever, binding two consecutive elements from it to $a and $b, until whatever is empty. If it has an odd number of elements, one might write:
for whatever -> $a, $b? { say $a + $b }
And so on.
Bottom line: a huge number of occurrences of {...} in Raku are IIFEs, even if they don't look like it. But if they're immediately after an =, Raku defaults to assuming you want to assign the lambda rather than immediately executing it, so you need to insert a do in that particular case.
Welcome to Raku!
my $x = BEGIN {
say "Hi!";
my $a = 2;
my $b = 3;
$a + $b;
}
I guess the common ancestry of Raku and Ruby shows :-)
Also note that to create a constant, you can also use constant:
my constant $x = do {
say "Hi!";
my $a = 2;
my $b = 3;
$a + $b;
}
If you can have a single statement, you can leave off the braces:
my $x = BEGIN 2 + 3;
or:
my constant $x = 2 + 3;
Regarding blocks: if they are in sink context (similar to "void" context in some languages), then they will execute just like that:
{
say "Executing block";
}
No need to explicitely call it: it will be called for you :-)
In a for loop, a different variable is assigned a value. The variable which has already been assigned a value is getting assigned the value from next iteration. At the end, both variable have the same value.
The code is for validating data in a file. When I print the values, it prints correct value for first iteration but in the next iteration, the value assigned in first iteration is changed.
When I print the value of $value3 and $value4 in the for loop, it shows null for $value4 and some value for $value3 but in the next iteration, the value of $value3 is overwritten by the value of $value4
I have tried on rakudo perl 6.c
my $fh= $!FileName.IO.open;
my $fileObject = FileValidation.new( file => $fh );
for (3,4).list {
put "Iteration: ", $_;
if ($_ == 4) {
$value4 := $fileObject.FileValidationFunction(%.ValidationRules{4}<ValidationFunction>, %.ValidationRules{4}<Arguments>);
}
if ($_ == 3) {
$value3 := $fileObject.FileValidationFunction(%.ValidationRules{3}<ValidationFunction>, %.ValidationRules{3}<Arguments>);
}
$fh.seek: SeekFromBeginning;
}
TL;DR It's not possible to confidently answer your question as it stands. This is a nanswer -- an answer in the sense I'm writing it as one but also quite possibly not an answer in the sense of helping you fix your problem.
Is it is rw? A first look.
The is rw trait on a routine or class attribute means it returns a container that contains a value rather than just returning a value.
If you then alias that container then you can get the behavior you've described.
For example:
my $foo;
sub bar is rw { $foo = rand }
my ($value3, $value4);
$value3 := bar;
.say for $value3, $value4;
$value4 := bar;
.say for $value3, $value4;
displays:
0.14168492246366005
(Any)
0.31843665763839857
0.31843665763839857
This isn't a bug in the language or compiler. It's just P6 code doing what it's supposed to do.
A longer version of the same thing
Perhaps the above is so far from your code it's disorienting. So here's the same thing wrapped in something like the code you provided.
spurt 'junk', 'junk';
class FileValidation {
has $.file;
has $!foo;
method FileValidationFunction ($,$) is rw { $!foo = rand }
}
class bar {
has $!FileName = 'junk';
has %.ValidationRules =
{ 3 => { ValidationFunction => {;}, Arguments => () },
4 => { ValidationFunction => {;}, Arguments => () } }
my ($value3, $value4);
method baz {
my $fh= $!FileName.IO.open;
my $fileObject = FileValidation.new( file => $fh );
my ($value3, $value4);
for (3,4).list {
put "Iteration: ", $_;
if ($_ == 4) {
$value4 := $fileObject.FileValidationFunction(
%.ValidationRules{4}<ValidationFunction>, %.ValidationRules{4}<Arguments>);
}
if ($_ == 3) {
$value3 := $fileObject.FileValidationFunction(
%.ValidationRules{3}<ValidationFunction>, %.ValidationRules{3}<Arguments>);
}
$fh.seek: SeekFromBeginning;
.say for $value3, $value4
}
}
}
bar.new.baz
This outputs:
Iteration: 3
0.5779679442816953
(Any)
Iteration: 4
0.8650280000277686
0.8650280000277686
Is it is rw? A second look.
Brad and I came up with essentially the same answer (at the same time; I was a minute ahead of Brad but who's counting? I mean besides me? :)) but Brad nicely nails the fix:
One way to avoid aliasing a container is to just use =.
(This is no doubt also why #ElizabethMattijsen++ asked about trying = instead of :=.)
You've commented that changing from := to = made no difference.
But presumably you didn't change from := to = throughout your entire codebase but rather just (the equivalent of) the two in the code you've shared.
So perhaps the problem can still be fixed by switching from := to =, but in some of your code elsewhere. (That said, don't just globally replace := with =. Instead, make sure you understand their difference and then change them as appropriate. You've got a test suite, right? ;))
How to move forward if you're still stuck
Right now your question has received several upvotes and no downvotes and you've got two answers (that point to the same problem).
But maybe our answers aren't good enough.
If so...
The addition of the reddit comment, and trying = instead of :=, and trying the latest compiler, and commenting on those things, leaves me glad I didn't downvote your question, but I haven't upvoted it yet and there's a reason for that. It's because your question is still missing a Minimal Reproducible Example.
You responded to my suggestion about producing an MRE with:
The problem is that I am not able to replicate this in a simpler environment
I presumed that's your situation, but as you can imagine, that means we can't confidently replicate it at all. That may be the way you prefer to go for reasons but it goes against SO guidance (in the link above) and if the current answers aren't adequate then the sensible way forward is for you to do what it takes to share code that reproduces your problem.
If it's large, please don't just paste it into your question but instead link to it. Perhaps you can set it up on glot.io using the + button to use multiple files (up to 6 I think, plus there's a standard input too). If not, perhaps gist it via, say, gist.github.com, and if I can I'll set it up on glot.io for you.
What is probably happening is that you are returning a container rather than a value, then aliasing the container to a variable.
class Foo {
has $.a is rw;
}
my $o = Foo.new( a => 1 );
my $old := $o.a;
say $old; # 1
$o.a = 2;
say $old; # 2
One way to avoid aliasing a container is to just use =.
my $old = $o.a;
say $old; # 1
$o.a = 2;
say $old; # 1
You could also decontainerize the value using either .self or .<>
my $old := $o.a.<>;
say $old; # 1
$o.a = 2;
say $old; # 1
(Note that .<> above could be .self or just <>.)
I keep wanting to do something like this:
my $block := {
state $n = 0;
say $n++;
last if $n > 3;
};
loop $block;
Or even:
$block.loop;
I'm not expecting that this is possible but it would sure be cool if it was.
How would I find out where a particular routine comes from?
$ perl6
To exit type 'exit' or '^D'
> &loop.^name
===SORRY!=== Error while compiling:
Undeclared routine:
loop used at line 1
Making $block.loop work, is rather easy and could live in module land:
use MONKEY;
augment class Block {
method loop($self:) {
Nil while $self()
}
}
my $a = { print "a" };
$a.loop # aaaaaaaaaaaaaaaaaaa (with apologies to Knorkator)
Making loop $block work would be rather more involved, as this would involve changes to the action handling of the Perl 6 grammar.
Using what is already in Perl 6, you can use Seq.from-loop in sink context.
(Note that the REPL doesn't put the last statement on a line into sink context)
my $block := {
state $n = 0;
say $n++;
last if $n > 3;
}
Seq.from-loop: $block;
Seq.from-loop: {say $++}, {$++ <= 3};
I am trying to generate FASTQ files containing 10 random sequences with random quality scores. I originally used the following code, which worked fine:
my #seq = (rand_fa_seq() for ^10);
my #qual = (rand_qual() for ^10);
#seq.perl.say;
#qual.perl.say;
sub rand_fa_seq
{
return join("", roll(20,"ACGT".comb));
}
sub rand_qual
{
return join("", roll(20,"EFGHIJ".comb))
}
However, wanting to simplify it even more, I thought that perhaps I could remove the parentheses from around the right hand statement. When I did so, I only got a single element in #seq and #qual.
my #seq = rand_fa_seq() for ^10;
my #qual = rand_qual() for ^10;
#seq.perl.say;
#qual.perl.say;
sub rand_fa_seq
{
return join("", roll(20,"ACGT".comb));
}
sub rand_qual
{
return join("", roll(20,"EFGHIJ".comb))
}
Is this a bug or is this the way it should behave? Without the parentheses is this a scalar context? Will the Great List Refactor change this behavior?
Versions of Perl 6 interpreters in which I have seen this behavior:
MoarVM:
perl6 version 2015.03-204-g8578022 built on MoarVM version 2015.03-60-g36d56f7
JVM:
perl6 version 2015.03-305-ga95107d built on JVM
java version "1.7.0_79"
OpenJDK Runtime Environment (rhel-2.5.5.1.el7_1-x86_64 u79-b14)
OpenJDK 64-Bit Server VM (build 24.79-b02, mixed mode)
Statement modifiers are one of the hallmarks of Perl syntax (cf Perl 5's perldoc), and they survived the transition to version 6.
This means your statements are equivalent to
my #seq;
for ^10 { #seq = rand_fa_seq() }
my #qual;
for ^10 { #qual = rand_qual() }
ie you're assigning a fresh value 10 times in a row (and only the last one survives).
Note that this could also be written more succintly as
my #seq = rand_fa_seq() xx 10;
my #qual = rand_qual() xx 10;
Also note that by default, the last statement in a sub provides the return value.
Assuming you might need sequences of length other than 20, you could parametrize that value, ending up with the following:
sub rand-fa-seq($n = 20) { <A C G T>.roll($n).join }
sub rand-qual($n = 20) { <E F G H I J>.roll($n).join }
my #seq = rand-fa-seq() xx 10;
my #qual = rand-qual() xx 10;
where I've used quote words instead of splitting a string.
The second example is like the classical perl5 control statements at the end of the line.
Like
say "true" if something();
say "yeah" for ^10;
if you would put a print statement within rand_qual() you would notice that it's still being executed 10 times.