为什么perl会解析$ x | $ y | $ z为$ z | ($ x | $ y)？

Question

(编辑:pipe下面的函数应返回一个受祝福的对象,以便重载正常工作.请参阅接受的答案.)

我正在尝试使用perl的overload功能来构建一个简单的解析树.我不需要太多 - 实际上,我只需要一个左关联的运算符.但是,perl解析$x op $y与更长链的解决方式似乎存在不一致$x op $y op $z op ....

这就是我所拥有的:

package foo;

use overload '|' => \&pipe,
             "**" => \&pipe,
             ">>" => \&pipe;

sub pipe { [ $_[0], $_[1] ] }

package main;

my $x = bless ["x"], "foo";
my $y = bless ["y"], "foo";
my $z = bless ["z"], "foo";
my $w = bless ["w"], "foo";

                               # how perl parses it:
my $p2 = $x | $y;              # Cons x y
my $p3 = $x | $y | $z;         # Cons z (Cons x y)
my $p4 = $x | $y | $z | $w;    # Cons w (Cons z (Cons x y))
my $p5 = $z | ($x | $y);       # same as p3???

my $s2 = $x ** $y;             # Cons x y
my $s3 = $x ** $y ** $z;       # Cons x (Cons y z)
my $s4 = $x ** $y ** $z ** $w; # Cons x (Cons y (Cons z w))

sub d { Dumper(\@_) }

say "p2 = ".d($p2);
say "p3 = ".d($p3);
say "p4 = ".d($p4);
say "p5 = ".d($p5);

say "s2 = ".d($s2);
say "s3 = ".d($s3);
say "s4 = ".d($s4);

输出类似于:

p2 = [bless( ['x'], 'foo' ),bless( ['y'], 'foo' )]
p3 = [bless( ['z'], 'foo' ),[bless( ['x'], 'foo' ),bless( ['y'], 'foo' )]]
p4 = [bless( ['w'], 'foo' ),[bless( ['z'], 'foo' ),[bless( ['x'], 'foo' ),bless( ['y'], 'foo' )]]]
p5 = [bless( ['z'], 'foo' ),[bless( ['x'], 'foo' ),bless( ['y'], 'foo' )]]

s2 = [bless( ['x'], 'foo' ),bless( ['y'], 'foo' )]
s3 = [bless( ['x'], 'foo' ),[bless( ['y'], 'foo' ),bless( ['z'], 'foo' )]]
s4 = [bless( ['x'], 'foo' ),[bless( ['y'], 'foo' ),[bless( ['z'], 'foo' ),bless( ['w'], 'foo' )]]]

不应该p2将x和y颠倒以与其他情况一致吗？注意p3并p5产生相同的输出 - 所以我怎么能分开它们？

我没有看到右关联运算符的相同问题**.

有没有解决这个问题？

Answer 1

use feature ":5.14";
use warnings FATAL => qw(all);
use strict;
use Data::Dump qw(dump pp);

sub foo() 
 {package foo;

  use overload '|' => \&p;

  sub p {bless [@{$_[0]},@{$_[1]}]}
 }

my $x = bless ["x"], "foo";
my $y = bless ["y"], "foo";
my $z = bless ["z"], "foo";

my $p = $x | $y | $z;

pp($p)

生产：

bless(["x", "y", "z"], "foo")