代码: 全选
[5, "+", [[3, "-", 9], "/", 7]]
(29/7)
[[[2, "/", 7], "+", 3], "-", [9, "/", 21]]
(20/7)
自己实现部分功能可以熟悉一下重载。
Code: [show] | [select all]
=info
表达式抽象语法树 转 有理数运算
523066680/vicyang
2019-04
=cut
use feature 'say';
use Data::Dump qw/dd/;
STDOUT->autoflush(1);
my $exp1 = [ 5, '+', [[ 3, '-', 9 ], '/', 7 ]];
my $exp2 = [[[2,'/',7], '+', 3], '-', [9, '/', 21]];
dd $exp1;
say extract( $exp1, 0 );
dd $exp2;
say extract( $exp2, 0 );
sub extract
{
my ($exp, $lv) = @_;
my $ret;
for my $e ( @{$exp}[0,2] ) {
$e = ref $e ? extract( $e, $lv+1 ) : fract->new($e, 1);
}
eval( "\$ret = \$exp->[0] $exp->[1] \$exp->[2]" );
return $ret;
}
{
package fract;
use overload '+' => \&add, '-' => \&sub,
'*' => \&mul, '/' => \&div,
q("") => \&as_string; #sub { return $_[0] };
sub new {
my ($class, $n, $m) = @_;
bless [$n, $m], $class;
}
sub add {
my ($a, $b) = @_;
my $n = $a->[0]*$b->[1] + $b->[0]*$a->[1];
my $m = $a->[1]*$b->[1];
return bless [$n, $m], ref($a);
}
sub sub {
my ($a, $b) = @_;
my $n = $a->[0]*$b->[1] - $b->[0]*$a->[1];
my $m = $a->[1]*$b->[1];
return bless [$n, $m], ref($a);
}
sub mul {
my ($a, $b) = @_;
my $n = $a->[0]*$b->[0];
my $m = $a->[1]*$b->[1];
return bless [$n, $m], ref($a);
}
sub div {
my ($a, $b) = @_;
my $n = $a->[0]*$b->[1];
my $m = $a->[1]*$b->[0];
return bless [$n, $m], ref($a);
}
sub as_string {
my ($f) = @_;
reduce($f);
return sprintf "(%d/%d)", $f->[0], $f->[1];
}
sub reduce {
my ($f) = @_;
my ($a, $b) = @$f;
while ( $b != 0 ) {
my $t = $b;
$b = $a % $b;
$a = $t;
}
$f->[0] /= $a;
$f->[1] /= $a;
}
1;
}