Perl 5.005_03 on obsidian as a target for modern Perl - prediction log.
Author: Claude Opus 5.5 (claude-opus-5-5). Series letter: V.
Written BEFORE running any of these constructs on obsidian's Perl 5.005_03, and before
listing its library directory. Format: ID [confidence] claim.
"Compile error" means perl -c fails; "run-time error" means it compiles and dies when run;
"silent" means it runs without an error message but does something other than intended.

Already observed on 2026-10-07/08 while porting NSI v4 (not predictions, not scored):
use warnings fails (no warnings.pm); 3-argument open is a compile error ("Too many
arguments for open"); Time::HiRes is missing; open(STDERR, '>&', STDOUT) fails to compile
under strict (bareword STDOUT); an undefined lexical used as a file handle dies at run time
("Can't use an undefined value as filehandle reference"); Symbol::gensym, Cwd, Getopt::Long,
File::Basename and POSIX load; while (<FH>) clobbers the caller's $_, and inside map it
empties the list being mapped; Perl starts in about 0.02 s, use POSIX adds about 0.12 s.

--- round 1 ---
V01 [0.85] no warnings; fails the same way as use warnings (cannot locate warnings.pm).
V02 [0.90] use 5.006; fails at compile time, naming the running version as 5.00503.
V03 [0.55] our $x; is a compile-time syntax error.
V04 [0.70] $x // 1 (defined-or) is a compile-time error.
V05 [0.60] say "hi"; compiles and dies at run time with "Undefined subroutine &main::say".
V06 [0.80] use constant FOO => 1; works.
V07 [0.65] use constant { A => 1, B => 2 }; (several constants at once) fails or defines
     something other than A and B.
V08 [0.90] qr// works.
V09 [0.75] The \z regex anchor works.
V10 [0.80] Lookbehind (?<=...) works.
V11 [0.60] sprintf("%vd", "1.22.333") does not produce "1.22.333".
V12 [0.50] exists &foo is a compile-time error.
V13 [0.70] binmode(STDOUT, ':utf8') is a compile-time error (too many arguments).
V14 [0.60] use utf8; fails (no utf8.pm).
V15 [0.70] $^V is undefined (prints as an empty string).
V16 [0.70] File::Spec loads.
V17 [0.80] File::Temp is missing.
V18 [0.85] Scalar::Util is missing.
V19 [0.85] List::Util is missing.
V20 [0.85] Data::Dumper loads.
V21 [0.80] CGI.pm loads.
V22 [0.50] CGI.pm's version is below 2.50.
V23 [0.80] Digest::MD5 is missing.
V24 [0.75] Storable is missing.
V25 [0.80] IO::File loads.
V26 [0.60] while (my $line = <FH>) processes a final line consisting of "0" with no newline
     (the implicit defined() test exists in 5.005).
V27 [0.90] A key/value hash slice %h{'a','b'} is a compile-time error.
V28 [0.55] sort { $a <=> $b } with a named sub (sort by_num @x) and a sub that uses $a/$b
     declared in the same package works; tested as plain sort-by-name, it works.
Fri Oct  9 12:14:03 PM MDT 2026

=== OUTCOMES (scored 2026-10-09) ===
Evidence: tests/V01.pl-V28.pl run on obsidian with /usr/bin/perl 5.005_03 (perl -c, then a
run); results-5005.txt. The same files on Perl 5.32.1 for contrast: results-532.txt.
V01 HIT      [0.85] "Can't locate warnings.pm in @INC".
V02 HIT      [0.90] "Perl 5.006 required--this is only version 5.00503".
V03 PARTIAL  [0.55] a compile-time error, but not a syntax error: `our` parses as a call to a
     sub named our, and the error is "Can't modify subroutine entry in scalar assignment".
V04 HIT      [0.70] "Search pattern not terminated": // starts an empty pattern match.
V05 MISS     [0.60] a compile-time error, not a run-time one: "String found where operator
     expected ... (Do you need to predeclare say?)". Perl 5.32 says the same without
     use feature 'say'.
V06 HIT      [0.80] works.
V07 HIT      [0.65] dies at compile time: "Can't define "HASH(0x...)" as constant".
V08 HIT      [0.90] works.
V09 HIT      [0.75] works.
V10 HIT      [0.80] works.
V11 HIT      [0.60] prints "%vd" literally (no %v format). The test was weak: on 5.32 it prints
     49.46.50.50.46.51.51.51, the codes of a plain string's characters, which is correct.
V12 HIT      [0.50] "exists operator argument is not a HASH element".
V13 MISS     [0.70] compiles and runs. Silent: binmode takes one argument in 5.005, so the
     layer parses as a separate expression and is ignored; only -w says anything ("Useless
     use of a constant in void context").
V14 HIT      [0.60] "Can't locate utf8.pm".
V15 HIT      [0.70] $^V undefined.
V16 HIT      [0.70] loads; catfile works.
V17 HIT      [0.80] missing.
V18 HIT      [0.85] missing.
V19 HIT      [0.85] missing.
V20 HIT      [0.85] loads.
V21 HIT      [0.80] loads (and is missing from Perl 5.32, which dropped it from core).
V22 HIT      [0.50] version 2.46.
V23 HIT      [0.80] missing.
V24 HIT      [0.75] missing.
V25 HIT      [0.80] loads.
V26 HIT      [0.60] both lines counted, including the final "0".
V27 HIT      [0.90] "Can't use subscript on private hash".
V28 HIT      [0.55] the claim is badly worded (two claims in one); scored on its last clause:
     sort with a named sub using $a/$b works (1 9 10 100).

Calibration:  <0.50: none   0.50-0.79: 12/15 (V03 partial, V05 and V13 miss)   >=0.80: 13/13
Not predicted: binmode's second argument is silently dropped rather than rejected; `our` fails
as an assignment to a sub call; say fails at compile time even on modern Perl without the
feature; CGI.pm is present in 5.005 but absent from modern Perl's core.