Pff, c'est tendu... Pour le fun :

!/usr/bin/env perl

use Data::Dumper qw(Dumper);

my $FROM_JSON = qr{

(?&VALUE) (?{ $_ = $^R->[1] })

(?(DEFINE)

(?<OBJECT>
(?{ [$^R, {}] })
{
(?: (?&KV) # [[$^R, {}], $k, $v]
(?{ # warn Dumper { obj1 => $^R };
[$^R->[0][0], {$^R->[1] => $^R->[2]}] })
(?: , (?&KV) # [[$^R, {...}], $k, $v]
(?{ # warn Dumper { obj2 => $^R };
[$^R->[0][0], {%{$^R->[0][1]}, $^R->[1] => $^R->[2]}] })
)*
)?
}
)

(?<KV>
(?&STRING) # [$^R, "string"]
: (?&VALUE) # [[$^R, "string"], $value]
(?{ # warn Dumper { kv => $^R };
[$^R->[0][0], $^R->[0][1], $^R->[1]] })
)

(?<ARRAY>
(?{ [$^R, []] })
[
(?: (?&VALUE) (?{ [$^R->[0][0], [$^R->[1]]] })
(?: , (?&VALUE) (?{ # warn Dumper { atwo => $^R };
[$^R->[0][0], [@{$^R->[0][1]}, $^R->[1]]] })
)*
)?
]
)

  (?&OBJECT)
|
  (?&ARRAY)
|
true (?{ [$^R, 1] })

null (?{ [$^R, undef] })

)
\s*
)

(?<STRING>
(
"
(?:
[^\"]+
|
\ ["\/bfnrt]

|

\ u [0-9a-fA-f]{4}

)*
"

)

(?{ [$^R, eval $^N] })
)

(?<NUMBER>
(
-?
(?: 0 | [1-9]\d* )
(?: . \d+ )?
(?: [eE] [-+]? \d+ )?
)

(?{ [$^R, eval $^N] })
)

) }xms;

sub fromjson {
local $ = shift;
local $^R;
eval { m{\A$FROMJSON\z}; } and return $;
die $@ if $@;
return 'no match';
}

while (<>) {
chomp;
print Dumper fromjson($);
}