# HG changeset patch
# User HackEso <hackeso@esolangs.org>
# Date 1563586235 0
# Node ID d0cc5812f4bb937fb79fd0d0ad6960da2eb973f3
# Parent  766bdea3dbe936bb174597c3987c07440ac4e1a6
<ais523> ` mv 7.pl interps/7

diff -r 766bdea3dbe9 -r d0cc5812f4bb 7.pl
--- a/7.pl	Sat Jul 20 01:30:00 2019 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,622 +0,0 @@
-#!/usr/bin/env perl
-use utf8;
-q{
-
-=pod
-
-=encoding UTF8
-
-=head1 NAME
-
-7 - an esoteric programming language
-
-=head1 SYNOPSIS
-
-./7 program.7      # run
-./7 -d program.7   # debug
-
-=head1 DESCRIPTION
-
-7 is an esoteric programming language, inspired by Underload (although
-it has diverged somewhat), but aiming for small source code
-representation.
-
-The language operates using two main pieces of internal state: the
-I<frame>, which is a vaguely stack-like construct that holds data; and
-the I<command list>.  The frame consists of a sequence of commands
-separated by I<bars>; the command list is also a sequence of commands.
-
-The program operates by repeatedly removing the first command from the
-command list, then performing the action specified by that command on
-the frame.  Once the command list is empty, the portion of the frame
-to the right of the last bar is copied to the start of the command
-list; this operation is called "cycling".  (Cycling exits the program
-if the frame is completely empty, and is an error if the frame is
-nonempty but has no bars; also, as a special case, it deletes the
-rightmost bar if nothing is to its right, in order to avoid a trivial
-infinite loop.)  These are the only ways in which the command list can
-be modified.
-
-The frame is a "working space" for the program, and so can be modified
-in rather more interesting ways than the command list.  However,
-typically only the section to the right of the rightmost bar is
-modified, so operations tend to be fairly local and self-contained.
-
-=head2 Frame operations
-
-There is a range of basic operations that can be performed on the
-frame:
-
-=over 4
-
-=item *
-
-You can I<append> something to the frame, either a bar or a command.
-This adds the bar or command in question to the right of the frame.
-
-=item *
-
-You can I<disbar> the frame, removing the rightmost bar ("closing the
-gap" where the bar was in the process).
-
-=item *
-
-You can I<copy> a section of the frame to the end.  A section is the
-region of the frame between two bars, or from a bar to an end of the
-frame.  When copying a section, a bar is placed to separate the copy
-from the rest of the frame.
-
-=item *
-
-You can I<move> a section of the frame to the end.  This is like
-copying, except that original section (together with one of the bars
-between it and the adjacent sections) is removed.
-
-=item *
-
-You can I<delete> the end of the frame, again from the rightmost bar
-onwards.  This will delete the bar in the process.
-
-=item *
-
-You can I<output> the end of the frame to the user.  This outputs the
-area strictly beyond the rightmost bar.  (Bars themselves are never
-output, because they have no representation as a sequence of bits.)
-
-=item *
-
-You can I<pacify> the end of the frame, beyond the rightmost bar; this
-is the most complex operation.  To understand this, the first thing to
-note is that the commands come in pairs; each I<active> command is
-paired with a I<passive> command.  Additionally, some commands have
-names, and some do not have names, We can then describe the process as
-follows:
-
-=over 4
-
-=item 1.
-
-The "passive regions" of the section are identified.  These are
-regions in which all the commands are named, and for which C<7> and
-C<6> commands are correctly matched, as though they were parentheses;
-additionally, the substring C<76> cannot appear in a passive region.
-Passive regions are made as long as possible while respecting these
-rules.
-
-=item 2.
-
-Each passive region is enclosed between a C<7> and C<6> command.
-
-=item 3.
-
-Each command outside any passive region (which must by definition be
-active, as all anonymous commands are active, as are C<6> and C<7>) is
-converted to the corresponding passive command.
-
-=back
-
-=back
-
-=head2 Commands
-
-Now that we've defined the basic frame operations, it's possible to
-define the commands.
-
-Eight of the twelve commands have numerical names, used in the source
-code representation: the six passive commands, and two active
-commands.  The other four active commands have no numerical name (and
-cannot appear in the source), and are given names in English to
-identify them.
-
-=over 4
-
-=item C<6> (active), C<0> (passive): Pacify then disbar
-
-The C<6> command pacifies the rightmost section of the frame, and then
-the frame is disbarred.  The passive equivalent C<0> appends a C<6>
-command to the frame.
-
-=item C<7> (active), C<1> (passive): Append a bar
-
-The C<7> command appends a bar to the frame.  The passive equivalent
-C<1> appends a C<7> command to the frame.
-
-=item "copy" (active), C<2> (passive): Copy the rightmost section
-
-The "copy" command copies the rightmost section of the frame to the
-end of the frame.  The passive equivalent C<2> appends a "copy"
-command to the frame.
-
-=item "recycle" (active) C<5> (passive): Cycle early, then delete
-
-The "recycle" command cycles a copy of the rightmost section of the
-frame onto the command list, even if the command list isn't empty.
-After doing that, it deletes the rightmost section of the frame
-(including the bar that separates it from the rest of the frame).  The
-passive equivalent C<5> appends a "recycle" command to the frame.
-
-=item "grab" (active), C<4> (passive): Swap, with extra bars
-
-The "grab" command appends an extra bar to the frame then moves the
-new third-rightmost section (the original second-rightmost section) of
-the frame to the end of the frame.  The passive equivalent C<4>
-appends a "grab" command to the frame. 
-
-=item "eject" (active), C<3> (passive): Output, then delete twice
-
-The "eject" command outputs the end of the frame (beyond the rightmost
-bar) to the user, then deletes the end of the frame from the
-second-rightmost bar onwards (i.e. deletes the end of the frame
-twice).  Exception: if the section of the frame that would be output
-contains any unnamed commands, it is pacified first (pacification
-leaves a region with only named commands), and a C<7> is prepended to
-the output.  The passive equivalent C<3> appends an "eject" command to
-the frame.
-
-This command is also capable of producing input in some circumstances
-(via outputting special codes which mean "read input").  Although the
-input can be in more than one form, it's always provided to the
-program as a nonnegative integer, and affects the program like this:
-after the deletions from the frame, the new rightmost section of the
-frame (not including the bar to its left) has its content repeated a
-number of times equal to the input (e.g. 0 would remove everything to
-the right of the rightmost bar, 1 would do nothing, 2 would add an
-extra copy of the text to the rightmost bar, and so on.)  When reading
-in integers from the user, any leading whitespace and commas are
-skipped, then a decimal integer is read, with any stray characters
-"after" the integer being left for future input commands; if there's
-no integer available, 0 will be returned (this is also a valid
-integer, so you may want to alternate between character and integer
-reading to detect invalid input and EOF).  When reading in characters,
-they're converted to a character code, and 1 is added to them (EOF
-counts as character code -1, and thus will produce 0 copies).
-
-The very first command output via this command does not produce
-output, but rather specifies the format of future output:
-
-=over 4
-
-=item Numerical (C<0>)
-
-In each command list output, a value is calculated like this: the
-total number of C<7> and C<1> commands, minus the total number of C<6>
-and C<0> commands.  Exception: if the output was automatically
-pacified (and thus had a C<7> prepended), that C<7> does not count in
-the total count of C<7> commands.  This integer is converted to
-decimal and output.
-
-Formatting can be controlled via outputting commands other than
-strings of C<0>, C<1>, C<6>, C<7>.  The output will be preceded by a
-space, unless it's the first output on the line.  A C<2> at the end of
-the string will output a trailing newline. A C<3> at the end of the
-string will append a comma to it. C<4> and C<5> can be placed at
-either end of the string, and will turn into opening and closing
-square brackets respectively.
-
-Input can be obtained via attempting to output C<23> (numerical input)
-or C<24> (character input).  Outputting C<25> allows selection of a
-new output format (basically by "resetting" the format, meaning that
-the next command to be output will select a format again).
-
-=item Byte-per-command (C<1>)
-
-Each command is output as an individual byte (thus the only bytes
-output will be the digits C<0> to C<7> inclusive, as those are the
-only bytes that name commands).  This format does not support input.
-
-=item Character code as number (C<2>)
-
-This is similar to the numerical output C<0> explained above, except
-that 1 is subracted from the number, and it's then used as a character
-code (rather than being output in decimal).  By default, this is in
-binary (i.e. octets mod 256), but this can be changed by attempting to
-output a negative number; C<-1> selects binary, C<-2> selects UTF-8,
-C<-3> inputs a number, C<-4> inputs a character, and C<-5> allows
-selection of a new output format.  Commands other than C<0>, C<1>,
-C<6>, and C<7> aren't recognised here.
-
-=item Byte-per-three-commands (C<3>)
-
-Any C<6> and C<7> commands in the output are ignored. The others are
-taken as triples and interpreted as base-6 numbers (as usual, in a
-big-endian way), giving a value from 0 to 215 (decimal), 0 to 555
-(base 6).  This is is encoded as follows: if the value is 127
-(decimal) or lower (that's 331 in base 6), it's output as an octet
-directly; if the value is in the range 128 to 191 (decimal) inclusive
-(that's 332 to 515 in base 6), then 64 (decimal), which is 144 (base
-6), might or might not be added to it.  Values above 192 (decimal) or
-520 (base 6) control this addition; outputting 522 (the default)
-requests the addition to happen in a way that makes the output look as
-much like UTF-8 as possible; 520 specifies never adding (until this
-condition is changed); 521 specifies always adding.  You can also
-request input, with 523 requesting an integer and 524 requesting a
-character; 525 allows selection of a new output format.  Other values
-are currently reserved for future expansion and should not be used.
-
-=item Truncated octal (C<4>)
-
-The output is encoded using the octal source encoding.  However, if it
-does not come to a whole number of bytes, any spare bits are discarded
-(as opposed to padding them out, as would for example happen with the
-source format C<7> when the source were in binary).  This format does
-not support input.
-
-=item US-TTY (C<5>)
-
-Any C<6> and C<7> commands in the output are ignored. The others are
-taken in pairs and interpreted as base-6 numbers (as usual, in a
-big-endian way), giving a value from 0 to 35 (decimal), 0 to 55 (base
-6).  These are then in turn interpreted as being in an expanded
-version of the US-TTY character set.  This is a 5-bit character set
-(thus using values from 0 to 31 (decimal), 0 to 51 (base 6)); the
-remaining four codes are reserved for giving instructions to the 7
-interpreter itself.  It can encode more than just 31 characters via
-the use of shift states; it has five different states, notated here as
-Ł, ł, Ŧ, Ø, ø, with Ł being the default.  (Ł and Ŧ are identical,
-except that immediately after outputting any character in state Ŧ, the
-shift state becomes ł; other shift states are stable until changed
-explicitly. State ø is an expansion based on CLC-INTERCAL's version of
-Baudot, a very similar character set to US-TTY; US-TTY reserves the
-state for use by expansions but does not specify what form those might
-take. Note that the tables below are not I<quite> the same as
-CLC-INTERCAL's, although they are very close; however, the only
-differences are in the meanings of some shift codes, and in the fact
-that C<#> appears in two places in order to improve compatibility with
-existing US-TTY and CLC-INTERCAL-encoded text.) The character (or
-control sequence) encoded depends on the shift state and the sequence
-seen.
-
-Here's how the character set looks (shift state down the left side,
-character encoding (first then second command) at the top, Ŧ encodes
-the same characters as Ł):
-
-   00000011111122222233333344444455
-   01234501234501234501234501234501
-  
- Ł  E A SIU DRJNFCKTZLWHYPQOBGØMXVł
- ł  e a siu drjnfcktzlwhypqobgØmxvŦ
- Ø  3 -  87 $4',!:(5")2#6019?&ø./;Ł
- ø  ¢ + \#= *{~∀|^<[}>] @ £¬  Ø%_ Ł
-
-C<00> encodes NUL, C<02> encodes newline, C<04> encodes space, C<12>
-encodes carriage return, C<05> in state Ø encodes BEL, C<32> in state
-ø encodes backspace, C<41> in state ø encodes DEL, other blank squares
-are currently undefined and should not be used.
-
-As for the remaining codes, C<53> requests input of an integer, C<54>
-requests input of a character, and C<55> allows selection of a new
-output format.  C<52> is currently undefined and should not be used.
-
-=item Source (C<7>)
-
-The output is encoded the same way that the source was (and, if
-necessary, will be padded with C<1> bits; note that this padding only
-occurs if the program ends "naturally", not if it ends abruptly due to
-ejecting beyond the bottom of the stack).
-
-=item Other values
-
-Other values are currently undefined and reserved for future extension.
-
-=back
-
-If an attempt is made to delete more sections than exist on the frame
-via use of this command, the program exits immediately (although any
-output will still be produced).  (A program also exits if the frame
-and command list are both empty.)
-
-=back
-
-=head2 Source Encoding
-
-A 7 source file is written via the use of the eight named commands;
-the four anonymous commands cannot appear in the original
-program. These form the initial command list; the initial frame
-consists of two bars (with no commands before, after, or between
-them).  Additionally, it is not legal for a program to end with a C<7>
-command.  A file can either be written in ASCII, using one byte per
-command, or in octal, using three bits per command.  In the latter
-case, when storing the program in a file, the commands are written in
-such a way that the bit sequence of the commands and of the file are
-the same when viewed in a big-endian way.  If there's a need to pad
-the end of the program, e.g. to make it round up to a multiple of 8
-bits, the program can be padded by appending any number of C<1> bits
-(the fact that programs may not end with a C<7> command makes this
-unambiguous).  Similarly, any number of consecutive C<1> bits at the
-end of the file can be deleted (they're implied into the file when a
-partial command is seen).
-
-=cut
-
-} or exit;
-
-use warnings;
-use strict;
-use feature qw/state/;
-use Encode qw/encode/;
-use 5.012;
-
-my $debug;
-
-while (@ARGV && $ARGV[0] =~ /^-/) {
-    my $option = shift @ARGV;
-    $option eq '-d' ? $debug = 1 :
-    $option eq '-' ? last :
-    die "Unknown option $option";
-}
-
-my %usttytable = (
-    #        0   0 0000    11 11    1122222   233    333344      444455
-    #        0   1 2345    01 23    4501234   501    234501      234501
-    'Ł' => "\0"."E\nA S" ."IU\rD". "RJNFCKT".'ZLW'. "HYPQOB".   "GØMXVł",
-    'ł' => "\0"."e\na s" ."iu\rd". "rjnfckt".'zlw'. "hypqob".   "gØmxvŦ",
-    'Ø' => "\0"."3\n- \a"."87\r\$"."4',!:(5".'")2'. "#6019?".   "&ø./;Ł",
-    'ø' => "\0"."¢\n+ \\"."#=\r*". "{~∀|^<[".'}>]'."\b@—£¬\x7F"."—Ø%_—Ł");
-$usttytable{'Ŧ'} = $usttytable{'Ł'};
-
-$| = 1; undef $/;
-binmode STDIN;
-# Note: we leave STDOUT in text mode until the user selects an output format
-# that clearly requires binary.
-my $program = <>;
-my $program_was_binary = 0;
-my $bits_per_byte = length unpack "B*", "\0";
-
-if ($program =~ y/01234567 \n\r\t\f//c) {
-    # If the program contains anything other than digits, spaces, and
-    # \n,\r,\t,\f, then unpack it from binary.
-    my $binary = unpack "B*", $program;
-    $binary =~ s/1+$//;
-    $binary .= 1 while (length $binary) % 3;
-    $program = "";
-    $program .= oct "0b$&" while $binary =~ s/^...//;
-    $program_was_binary = 1;    
-} else {
-    $program =~ s/\s//g;
-}
-
-# Technically we should start with the program on the command list, but
-# it's easier to start it on the frame and do an explicit-cycle in order
-# to move it into place.
-my $frame = "|||$program";
-my $delayed_frame_copy = 1;
-my @commandlist = ();
-
-my $outformat = undef;
-
-sub pacify {
-    local $_ = shift;
-    s/((7(?2)+6|[0-5])+)/"7${1}6"=~y:67:89:r/ge;
-    y/67cegr89/0-7/;
-    $_;
-}
-
-my $pending_octal = "";
-my $getc_buffer = undef;
-
-sub getin {
-    if ($getc_buffer) {
-        my $c = $getc_buffer;
-        undef $getc_buffer;
-        $debug and printf STDERR "\tRereading character code $c\n";
-        return $c;
-    } else {
-        my $c = getc;
-        $c = defined $c ? (ord $c) + 1 : 0;
-        return $c;
-    }
-}
-
-sub input_number {
-    my $c;
-    my $n = 0;
-    while (($c = getin) && (chr $c - 1) =~ /\s/) {}
-    if (!$c) {
-        $debug and print STDERR "\tRead EOF, expecting number\n";
-        $delayed_frame_copy = 0;
-        return;
-    }
-    while ((chr $c - 1) =~ /(\d)/) {
-        $n *= 10;
-        $n += $1;
-        $c = getin;
-        !$c and last;
-    }
-    $getc_buffer = $c if $c;
-    $debug and print STDERR "\tRead integer value $n\n";
-    $delayed_frame_copy = $n;
-}
-
-sub input_char {
-    my $c = getin;
-    $debug and print STDERR (!$c ? "\tRead EOF, expecting character\n" :
-                             "Read character code ".($c - 1));
-    $delayed_frame_copy = $c;
-}
-
-sub oprint {
-    local $_ = shift;
-    my $autopacify = /\D/;
-    state $after_newline = 1;
-    $autopacify and $_ = "7" . pacify $_;
-    length $_ or return;
-
-    unless (defined $outformat) {
-        s/(.)//;
-        $outformat = $1;
-        $outformat == 7 and !$program_was_binary and $outformat = 1;
-        $debug and print STDERR "\tSelected output format $outformat\n";
-    }
-    [
-     sub { # 0: numerical
-         $_ eq '23' and input_number, return;
-         $_ eq '24' and input_char, return;
-         $_ eq '25' and (undef $outformat), return;
-         my $result = y/71//;
-         $result -= y/60//;
-         $result-- if $autopacify;
-         print " " unless $after_newline;
-         $after_newline = !!/2$/;
-         s/^[45]+// and print ($& =~ y/45/[]/r);
-         print $result;
-         s/[2345]+$// and print ($& =~ y/2345/\n,[]/r);
-     },
-     sub { # 1: byte per command
-         print;
-         $after_newline = 0;
-     },
-     sub { # 2: read numbers, write character codes
-         binmode STDOUT;
-         state $utf8mode = 0;
-         my $result = y/71//;
-         $result -= y/60//;
-         $result-- if $autopacify;
-         if ($result > 0) {
-             print $utf8mode ? encode("UTF-8", chr($result - 1)) :
-                 encode("ISO-8859-1", chr ($result - 1));
-         } else {
-             $result == -1 and ($utf8mode = 0), return;
-             $result == -2 and ($utf8mode = 1), return;
-             $result == -3 and input_number, return;
-             $result == -4 and input_char, return;
-             $result == -5 and (undef $outformat), return;
-             $result == 0 and die "Attempted to output EOF";
-             die "Attempted to output negative character code $result";
-         }
-     },
-     sub { # 3: byte per three commands
-         state $partial = "";
-         state $add64 = 194;
-         state $utf8bytes = 0;
-         binmode STDOUT;
-         s/[67]//g;
-         $partial .= $_;
-         while ($partial =~ s/^(.)(.)(.)//) {
-             my $v = $1*36 + $2 * 6 + $3;
-             if ($v < 128) {
-                 print chr $v;
-                 $utf8bytes = 0;
-             } elsif ($v < 192) {
-                 if ($add64 == 192 || ($add64 == 194 && $utf8bytes)) {
-                     print chr $v;
-                     $utf8bytes and $utf8bytes--;
-                 } elsif ($add64 == 193 || ($add64 == 194 && !$utf8bytes)) {
-                     $v += 64;
-                     print chr $v;
-                     $utf8bytes = 1; # always at least 1 trailing byte
-                     $v >= 0xE0 and ++$utf8bytes;
-                     $v >= 0xF0 and ++$utf8bytes;
-                     $v >= 0xF8 and ++$utf8bytes;
-                     $v >= 0xFC and ++$utf8bytes;
-                 }
-             } elsif ($v < 195) {
-                 $add64 = $v;
-             } elsif ($v == 195) {
-                 input_number;
-             } elsif ($v == 196) {
-                 input_char;
-             } elsif ($v == 197) {
-                 undef $outformat;
-             } else {
-                 die "Unknown byte-per-three-commands value $v";
-             }
-         }
-     },
-     sub { # 4: octal
-         state $partial = "";
-         binmode STDOUT;
-         $partial .= sprintf "%03b", $& while s/%.//;
-         print chr oct "0b$&" while $partial =~ s/^.{$bits_per_byte}//;
-     },
-     sub { # 5: US-TTY
-         s/[67]//g;
-         state $partial = "";
-         state $shiftstate = 'Ł';
-         $partial .= $_;
-         while ($partial =~ s/^(.)(.)//) {
-             my $v = $1 * 6 + $2;
-             $v == 33 and input_number, return;
-             $v == 34 and input_char, return;
-             $v == 35 and (undef $outformat), return;
-             my $c = substr $usttytable{$shiftstate}, $v, 1;
-             if ($usttytable{$c}) {
-                 $shiftstate = $c;
-             } elsif ($c eq '—') { # represents an invalid character
-                 ...;
-             } else {
-                 # TODO: Adapt to locale encoding?
-                 print encode("UTF-8",$c);
-                 $shiftstate eq 'Ŧ' and $shiftstate = 'ł';
-             }
-         }
-     },
-     sub { # 6: Unimplemented
-         die "Output format 6 is currently undefined";
-     },
-     sub { # 7: Like source; if we get here, it's octal encoding
-         binmode STDOUT;
-         $pending_octal .= sprintf "%03b", $& while s/^.//;
-         print chr oct "0b$&" while $pending_octal =~ s/^.{$bits_per_byte}//;
-     },
-    ]->[$outformat]->();
-    $debug and print STDERR "\n";
-}
-
-my $explicit = 1;
-CYCLE: while ($frame ne '') {
-    $frame =~ /[|](\w*)$/
-        or die "when cycling, frame is nonempty but has no bar";
-    my $commandlist = $1;
-    $commandlist eq '' and $explicit = 1;
-    $explicit and $frame =~ s/[|](\w*)$//;
-    $explicit = 0;
-    unshift @commandlist, split /([0-57]*)/, $commandlist;
-    while (@commandlist) {
-        if ($delayed_frame_copy != 1) {
-            $frame =~ s/[|]\K(\w*)$/$1 x $delayed_frame_copy/e
-                || die "Attempt to read input with no bar in the frame";
-            $delayed_frame_copy = 1;
-        }
-        $debug and print STDERR "\t$frame ", @commandlist, "\n";
-        my $command = shift @commandlist;
-        length $command or next;
-        for ($command) {
-            /[0-57]/ and $frame .= $command =~ y/0-57/67cegr|/r;
-            /6/ and $frame =~ s/[|](\w*)$/pacify $1/e
-                || die "6 command run with no bar in the frame";
-            /c/ and $frame =~ s/[|](\w*)$/|$1|$1/
-                || die "'copy' command run with no bar in the frame";
-            /e/ and $frame =~ s/[|]\w*[|](\w*)$/(oprint $1), ""/e
-                ||  $frame =~ s/(\w*)$/         (oprint $1), exit/e;
-            /g/ and $frame =~ s/(\w*)[|](\w*)$/$2||$1/
-                || die "'grab' command run with no bar in the frame";
-            /r/ and $explicit = 1 and next CYCLE;
-        }
-    }
-}
-
-$pending_octal =~ s/1+$//;
-if (length $pending_octal) {
-    $pending_octal .= 1 until length $pending_octal == $bits_per_byte;
-    print chr oct "0b$pending_octal";
-}
diff -r 766bdea3dbe9 -r d0cc5812f4bb interps/7/7.pl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/interps/7/7.pl	Sat Jul 20 01:30:35 2019 +0000
@@ -0,0 +1,622 @@
+#!/usr/bin/env perl
+use utf8;
+q{
+
+=pod
+
+=encoding UTF8
+
+=head1 NAME
+
+7 - an esoteric programming language
+
+=head1 SYNOPSIS
+
+./7 program.7      # run
+./7 -d program.7   # debug
+
+=head1 DESCRIPTION
+
+7 is an esoteric programming language, inspired by Underload (although
+it has diverged somewhat), but aiming for small source code
+representation.
+
+The language operates using two main pieces of internal state: the
+I<frame>, which is a vaguely stack-like construct that holds data; and
+the I<command list>.  The frame consists of a sequence of commands
+separated by I<bars>; the command list is also a sequence of commands.
+
+The program operates by repeatedly removing the first command from the
+command list, then performing the action specified by that command on
+the frame.  Once the command list is empty, the portion of the frame
+to the right of the last bar is copied to the start of the command
+list; this operation is called "cycling".  (Cycling exits the program
+if the frame is completely empty, and is an error if the frame is
+nonempty but has no bars; also, as a special case, it deletes the
+rightmost bar if nothing is to its right, in order to avoid a trivial
+infinite loop.)  These are the only ways in which the command list can
+be modified.
+
+The frame is a "working space" for the program, and so can be modified
+in rather more interesting ways than the command list.  However,
+typically only the section to the right of the rightmost bar is
+modified, so operations tend to be fairly local and self-contained.
+
+=head2 Frame operations
+
+There is a range of basic operations that can be performed on the
+frame:
+
+=over 4
+
+=item *
+
+You can I<append> something to the frame, either a bar or a command.
+This adds the bar or command in question to the right of the frame.
+
+=item *
+
+You can I<disbar> the frame, removing the rightmost bar ("closing the
+gap" where the bar was in the process).
+
+=item *
+
+You can I<copy> a section of the frame to the end.  A section is the
+region of the frame between two bars, or from a bar to an end of the
+frame.  When copying a section, a bar is placed to separate the copy
+from the rest of the frame.
+
+=item *
+
+You can I<move> a section of the frame to the end.  This is like
+copying, except that original section (together with one of the bars
+between it and the adjacent sections) is removed.
+
+=item *
+
+You can I<delete> the end of the frame, again from the rightmost bar
+onwards.  This will delete the bar in the process.
+
+=item *
+
+You can I<output> the end of the frame to the user.  This outputs the
+area strictly beyond the rightmost bar.  (Bars themselves are never
+output, because they have no representation as a sequence of bits.)
+
+=item *
+
+You can I<pacify> the end of the frame, beyond the rightmost bar; this
+is the most complex operation.  To understand this, the first thing to
+note is that the commands come in pairs; each I<active> command is
+paired with a I<passive> command.  Additionally, some commands have
+names, and some do not have names, We can then describe the process as
+follows:
+
+=over 4
+
+=item 1.
+
+The "passive regions" of the section are identified.  These are
+regions in which all the commands are named, and for which C<7> and
+C<6> commands are correctly matched, as though they were parentheses;
+additionally, the substring C<76> cannot appear in a passive region.
+Passive regions are made as long as possible while respecting these
+rules.
+
+=item 2.
+
+Each passive region is enclosed between a C<7> and C<6> command.
+
+=item 3.
+
+Each command outside any passive region (which must by definition be
+active, as all anonymous commands are active, as are C<6> and C<7>) is
+converted to the corresponding passive command.
+
+=back
+
+=back
+
+=head2 Commands
+
+Now that we've defined the basic frame operations, it's possible to
+define the commands.
+
+Eight of the twelve commands have numerical names, used in the source
+code representation: the six passive commands, and two active
+commands.  The other four active commands have no numerical name (and
+cannot appear in the source), and are given names in English to
+identify them.
+
+=over 4
+
+=item C<6> (active), C<0> (passive): Pacify then disbar
+
+The C<6> command pacifies the rightmost section of the frame, and then
+the frame is disbarred.  The passive equivalent C<0> appends a C<6>
+command to the frame.
+
+=item C<7> (active), C<1> (passive): Append a bar
+
+The C<7> command appends a bar to the frame.  The passive equivalent
+C<1> appends a C<7> command to the frame.
+
+=item "copy" (active), C<2> (passive): Copy the rightmost section
+
+The "copy" command copies the rightmost section of the frame to the
+end of the frame.  The passive equivalent C<2> appends a "copy"
+command to the frame.
+
+=item "recycle" (active) C<5> (passive): Cycle early, then delete
+
+The "recycle" command cycles a copy of the rightmost section of the
+frame onto the command list, even if the command list isn't empty.
+After doing that, it deletes the rightmost section of the frame
+(including the bar that separates it from the rest of the frame).  The
+passive equivalent C<5> appends a "recycle" command to the frame.
+
+=item "grab" (active), C<4> (passive): Swap, with extra bars
+
+The "grab" command appends an extra bar to the frame then moves the
+new third-rightmost section (the original second-rightmost section) of
+the frame to the end of the frame.  The passive equivalent C<4>
+appends a "grab" command to the frame. 
+
+=item "eject" (active), C<3> (passive): Output, then delete twice
+
+The "eject" command outputs the end of the frame (beyond the rightmost
+bar) to the user, then deletes the end of the frame from the
+second-rightmost bar onwards (i.e. deletes the end of the frame
+twice).  Exception: if the section of the frame that would be output
+contains any unnamed commands, it is pacified first (pacification
+leaves a region with only named commands), and a C<7> is prepended to
+the output.  The passive equivalent C<3> appends an "eject" command to
+the frame.
+
+This command is also capable of producing input in some circumstances
+(via outputting special codes which mean "read input").  Although the
+input can be in more than one form, it's always provided to the
+program as a nonnegative integer, and affects the program like this:
+after the deletions from the frame, the new rightmost section of the
+frame (not including the bar to its left) has its content repeated a
+number of times equal to the input (e.g. 0 would remove everything to
+the right of the rightmost bar, 1 would do nothing, 2 would add an
+extra copy of the text to the rightmost bar, and so on.)  When reading
+in integers from the user, any leading whitespace and commas are
+skipped, then a decimal integer is read, with any stray characters
+"after" the integer being left for future input commands; if there's
+no integer available, 0 will be returned (this is also a valid
+integer, so you may want to alternate between character and integer
+reading to detect invalid input and EOF).  When reading in characters,
+they're converted to a character code, and 1 is added to them (EOF
+counts as character code -1, and thus will produce 0 copies).
+
+The very first command output via this command does not produce
+output, but rather specifies the format of future output:
+
+=over 4
+
+=item Numerical (C<0>)
+
+In each command list output, a value is calculated like this: the
+total number of C<7> and C<1> commands, minus the total number of C<6>
+and C<0> commands.  Exception: if the output was automatically
+pacified (and thus had a C<7> prepended), that C<7> does not count in
+the total count of C<7> commands.  This integer is converted to
+decimal and output.
+
+Formatting can be controlled via outputting commands other than
+strings of C<0>, C<1>, C<6>, C<7>.  The output will be preceded by a
+space, unless it's the first output on the line.  A C<2> at the end of
+the string will output a trailing newline. A C<3> at the end of the
+string will append a comma to it. C<4> and C<5> can be placed at
+either end of the string, and will turn into opening and closing
+square brackets respectively.
+
+Input can be obtained via attempting to output C<23> (numerical input)
+or C<24> (character input).  Outputting C<25> allows selection of a
+new output format (basically by "resetting" the format, meaning that
+the next command to be output will select a format again).
+
+=item Byte-per-command (C<1>)
+
+Each command is output as an individual byte (thus the only bytes
+output will be the digits C<0> to C<7> inclusive, as those are the
+only bytes that name commands).  This format does not support input.
+
+=item Character code as number (C<2>)
+
+This is similar to the numerical output C<0> explained above, except
+that 1 is subracted from the number, and it's then used as a character
+code (rather than being output in decimal).  By default, this is in
+binary (i.e. octets mod 256), but this can be changed by attempting to
+output a negative number; C<-1> selects binary, C<-2> selects UTF-8,
+C<-3> inputs a number, C<-4> inputs a character, and C<-5> allows
+selection of a new output format.  Commands other than C<0>, C<1>,
+C<6>, and C<7> aren't recognised here.
+
+=item Byte-per-three-commands (C<3>)
+
+Any C<6> and C<7> commands in the output are ignored. The others are
+taken as triples and interpreted as base-6 numbers (as usual, in a
+big-endian way), giving a value from 0 to 215 (decimal), 0 to 555
+(base 6).  This is is encoded as follows: if the value is 127
+(decimal) or lower (that's 331 in base 6), it's output as an octet
+directly; if the value is in the range 128 to 191 (decimal) inclusive
+(that's 332 to 515 in base 6), then 64 (decimal), which is 144 (base
+6), might or might not be added to it.  Values above 192 (decimal) or
+520 (base 6) control this addition; outputting 522 (the default)
+requests the addition to happen in a way that makes the output look as
+much like UTF-8 as possible; 520 specifies never adding (until this
+condition is changed); 521 specifies always adding.  You can also
+request input, with 523 requesting an integer and 524 requesting a
+character; 525 allows selection of a new output format.  Other values
+are currently reserved for future expansion and should not be used.
+
+=item Truncated octal (C<4>)
+
+The output is encoded using the octal source encoding.  However, if it
+does not come to a whole number of bytes, any spare bits are discarded
+(as opposed to padding them out, as would for example happen with the
+source format C<7> when the source were in binary).  This format does
+not support input.
+
+=item US-TTY (C<5>)
+
+Any C<6> and C<7> commands in the output are ignored. The others are
+taken in pairs and interpreted as base-6 numbers (as usual, in a
+big-endian way), giving a value from 0 to 35 (decimal), 0 to 55 (base
+6).  These are then in turn interpreted as being in an expanded
+version of the US-TTY character set.  This is a 5-bit character set
+(thus using values from 0 to 31 (decimal), 0 to 51 (base 6)); the
+remaining four codes are reserved for giving instructions to the 7
+interpreter itself.  It can encode more than just 31 characters via
+the use of shift states; it has five different states, notated here as
+Ł, ł, Ŧ, Ø, ø, with Ł being the default.  (Ł and Ŧ are identical,
+except that immediately after outputting any character in state Ŧ, the
+shift state becomes ł; other shift states are stable until changed
+explicitly. State ø is an expansion based on CLC-INTERCAL's version of
+Baudot, a very similar character set to US-TTY; US-TTY reserves the
+state for use by expansions but does not specify what form those might
+take. Note that the tables below are not I<quite> the same as
+CLC-INTERCAL's, although they are very close; however, the only
+differences are in the meanings of some shift codes, and in the fact
+that C<#> appears in two places in order to improve compatibility with
+existing US-TTY and CLC-INTERCAL-encoded text.) The character (or
+control sequence) encoded depends on the shift state and the sequence
+seen.
+
+Here's how the character set looks (shift state down the left side,
+character encoding (first then second command) at the top, Ŧ encodes
+the same characters as Ł):
+
+   00000011111122222233333344444455
+   01234501234501234501234501234501
+  
+ Ł  E A SIU DRJNFCKTZLWHYPQOBGØMXVł
+ ł  e a siu drjnfcktzlwhypqobgØmxvŦ
+ Ø  3 -  87 $4',!:(5")2#6019?&ø./;Ł
+ ø  ¢ + \#= *{~∀|^<[}>] @ £¬  Ø%_ Ł
+
+C<00> encodes NUL, C<02> encodes newline, C<04> encodes space, C<12>
+encodes carriage return, C<05> in state Ø encodes BEL, C<32> in state
+ø encodes backspace, C<41> in state ø encodes DEL, other blank squares
+are currently undefined and should not be used.
+
+As for the remaining codes, C<53> requests input of an integer, C<54>
+requests input of a character, and C<55> allows selection of a new
+output format.  C<52> is currently undefined and should not be used.
+
+=item Source (C<7>)
+
+The output is encoded the same way that the source was (and, if
+necessary, will be padded with C<1> bits; note that this padding only
+occurs if the program ends "naturally", not if it ends abruptly due to
+ejecting beyond the bottom of the stack).
+
+=item Other values
+
+Other values are currently undefined and reserved for future extension.
+
+=back
+
+If an attempt is made to delete more sections than exist on the frame
+via use of this command, the program exits immediately (although any
+output will still be produced).  (A program also exits if the frame
+and command list are both empty.)
+
+=back
+
+=head2 Source Encoding
+
+A 7 source file is written via the use of the eight named commands;
+the four anonymous commands cannot appear in the original
+program. These form the initial command list; the initial frame
+consists of two bars (with no commands before, after, or between
+them).  Additionally, it is not legal for a program to end with a C<7>
+command.  A file can either be written in ASCII, using one byte per
+command, or in octal, using three bits per command.  In the latter
+case, when storing the program in a file, the commands are written in
+such a way that the bit sequence of the commands and of the file are
+the same when viewed in a big-endian way.  If there's a need to pad
+the end of the program, e.g. to make it round up to a multiple of 8
+bits, the program can be padded by appending any number of C<1> bits
+(the fact that programs may not end with a C<7> command makes this
+unambiguous).  Similarly, any number of consecutive C<1> bits at the
+end of the file can be deleted (they're implied into the file when a
+partial command is seen).
+
+=cut
+
+} or exit;
+
+use warnings;
+use strict;
+use feature qw/state/;
+use Encode qw/encode/;
+use 5.012;
+
+my $debug;
+
+while (@ARGV && $ARGV[0] =~ /^-/) {
+    my $option = shift @ARGV;
+    $option eq '-d' ? $debug = 1 :
+    $option eq '-' ? last :
+    die "Unknown option $option";
+}
+
+my %usttytable = (
+    #        0   0 0000    11 11    1122222   233    333344      444455
+    #        0   1 2345    01 23    4501234   501    234501      234501
+    'Ł' => "\0"."E\nA S" ."IU\rD". "RJNFCKT".'ZLW'. "HYPQOB".   "GØMXVł",
+    'ł' => "\0"."e\na s" ."iu\rd". "rjnfckt".'zlw'. "hypqob".   "gØmxvŦ",
+    'Ø' => "\0"."3\n- \a"."87\r\$"."4',!:(5".'")2'. "#6019?".   "&ø./;Ł",
+    'ø' => "\0"."¢\n+ \\"."#=\r*". "{~∀|^<[".'}>]'."\b@—£¬\x7F"."—Ø%_—Ł");
+$usttytable{'Ŧ'} = $usttytable{'Ł'};
+
+$| = 1; undef $/;
+binmode STDIN;
+# Note: we leave STDOUT in text mode until the user selects an output format
+# that clearly requires binary.
+my $program = <>;
+my $program_was_binary = 0;
+my $bits_per_byte = length unpack "B*", "\0";
+
+if ($program =~ y/01234567 \n\r\t\f//c) {
+    # If the program contains anything other than digits, spaces, and
+    # \n,\r,\t,\f, then unpack it from binary.
+    my $binary = unpack "B*", $program;
+    $binary =~ s/1+$//;
+    $binary .= 1 while (length $binary) % 3;
+    $program = "";
+    $program .= oct "0b$&" while $binary =~ s/^...//;
+    $program_was_binary = 1;    
+} else {
+    $program =~ s/\s//g;
+}
+
+# Technically we should start with the program on the command list, but
+# it's easier to start it on the frame and do an explicit-cycle in order
+# to move it into place.
+my $frame = "|||$program";
+my $delayed_frame_copy = 1;
+my @commandlist = ();
+
+my $outformat = undef;
+
+sub pacify {
+    local $_ = shift;
+    s/((7(?2)+6|[0-5])+)/"7${1}6"=~y:67:89:r/ge;
+    y/67cegr89/0-7/;
+    $_;
+}
+
+my $pending_octal = "";
+my $getc_buffer = undef;
+
+sub getin {
+    if ($getc_buffer) {
+        my $c = $getc_buffer;
+        undef $getc_buffer;
+        $debug and printf STDERR "\tRereading character code $c\n";
+        return $c;
+    } else {
+        my $c = getc;
+        $c = defined $c ? (ord $c) + 1 : 0;
+        return $c;
+    }
+}
+
+sub input_number {
+    my $c;
+    my $n = 0;
+    while (($c = getin) && (chr $c - 1) =~ /\s/) {}
+    if (!$c) {
+        $debug and print STDERR "\tRead EOF, expecting number\n";
+        $delayed_frame_copy = 0;
+        return;
+    }
+    while ((chr $c - 1) =~ /(\d)/) {
+        $n *= 10;
+        $n += $1;
+        $c = getin;
+        !$c and last;
+    }
+    $getc_buffer = $c if $c;
+    $debug and print STDERR "\tRead integer value $n\n";
+    $delayed_frame_copy = $n;
+}
+
+sub input_char {
+    my $c = getin;
+    $debug and print STDERR (!$c ? "\tRead EOF, expecting character\n" :
+                             "Read character code ".($c - 1));
+    $delayed_frame_copy = $c;
+}
+
+sub oprint {
+    local $_ = shift;
+    my $autopacify = /\D/;
+    state $after_newline = 1;
+    $autopacify and $_ = "7" . pacify $_;
+    length $_ or return;
+
+    unless (defined $outformat) {
+        s/(.)//;
+        $outformat = $1;
+        $outformat == 7 and !$program_was_binary and $outformat = 1;
+        $debug and print STDERR "\tSelected output format $outformat\n";
+    }
+    [
+     sub { # 0: numerical
+         $_ eq '23' and input_number, return;
+         $_ eq '24' and input_char, return;
+         $_ eq '25' and (undef $outformat), return;
+         my $result = y/71//;
+         $result -= y/60//;
+         $result-- if $autopacify;
+         print " " unless $after_newline;
+         $after_newline = !!/2$/;
+         s/^[45]+// and print ($& =~ y/45/[]/r);
+         print $result;
+         s/[2345]+$// and print ($& =~ y/2345/\n,[]/r);
+     },
+     sub { # 1: byte per command
+         print;
+         $after_newline = 0;
+     },
+     sub { # 2: read numbers, write character codes
+         binmode STDOUT;
+         state $utf8mode = 0;
+         my $result = y/71//;
+         $result -= y/60//;
+         $result-- if $autopacify;
+         if ($result > 0) {
+             print $utf8mode ? encode("UTF-8", chr($result - 1)) :
+                 encode("ISO-8859-1", chr ($result - 1));
+         } else {
+             $result == -1 and ($utf8mode = 0), return;
+             $result == -2 and ($utf8mode = 1), return;
+             $result == -3 and input_number, return;
+             $result == -4 and input_char, return;
+             $result == -5 and (undef $outformat), return;
+             $result == 0 and die "Attempted to output EOF";
+             die "Attempted to output negative character code $result";
+         }
+     },
+     sub { # 3: byte per three commands
+         state $partial = "";
+         state $add64 = 194;
+         state $utf8bytes = 0;
+         binmode STDOUT;
+         s/[67]//g;
+         $partial .= $_;
+         while ($partial =~ s/^(.)(.)(.)//) {
+             my $v = $1*36 + $2 * 6 + $3;
+             if ($v < 128) {
+                 print chr $v;
+                 $utf8bytes = 0;
+             } elsif ($v < 192) {
+                 if ($add64 == 192 || ($add64 == 194 && $utf8bytes)) {
+                     print chr $v;
+                     $utf8bytes and $utf8bytes--;
+                 } elsif ($add64 == 193 || ($add64 == 194 && !$utf8bytes)) {
+                     $v += 64;
+                     print chr $v;
+                     $utf8bytes = 1; # always at least 1 trailing byte
+                     $v >= 0xE0 and ++$utf8bytes;
+                     $v >= 0xF0 and ++$utf8bytes;
+                     $v >= 0xF8 and ++$utf8bytes;
+                     $v >= 0xFC and ++$utf8bytes;
+                 }
+             } elsif ($v < 195) {
+                 $add64 = $v;
+             } elsif ($v == 195) {
+                 input_number;
+             } elsif ($v == 196) {
+                 input_char;
+             } elsif ($v == 197) {
+                 undef $outformat;
+             } else {
+                 die "Unknown byte-per-three-commands value $v";
+             }
+         }
+     },
+     sub { # 4: octal
+         state $partial = "";
+         binmode STDOUT;
+         $partial .= sprintf "%03b", $& while s/%.//;
+         print chr oct "0b$&" while $partial =~ s/^.{$bits_per_byte}//;
+     },
+     sub { # 5: US-TTY
+         s/[67]//g;
+         state $partial = "";
+         state $shiftstate = 'Ł';
+         $partial .= $_;
+         while ($partial =~ s/^(.)(.)//) {
+             my $v = $1 * 6 + $2;
+             $v == 33 and input_number, return;
+             $v == 34 and input_char, return;
+             $v == 35 and (undef $outformat), return;
+             my $c = substr $usttytable{$shiftstate}, $v, 1;
+             if ($usttytable{$c}) {
+                 $shiftstate = $c;
+             } elsif ($c eq '—') { # represents an invalid character
+                 ...;
+             } else {
+                 # TODO: Adapt to locale encoding?
+                 print encode("UTF-8",$c);
+                 $shiftstate eq 'Ŧ' and $shiftstate = 'ł';
+             }
+         }
+     },
+     sub { # 6: Unimplemented
+         die "Output format 6 is currently undefined";
+     },
+     sub { # 7: Like source; if we get here, it's octal encoding
+         binmode STDOUT;
+         $pending_octal .= sprintf "%03b", $& while s/^.//;
+         print chr oct "0b$&" while $pending_octal =~ s/^.{$bits_per_byte}//;
+     },
+    ]->[$outformat]->();
+    $debug and print STDERR "\n";
+}
+
+my $explicit = 1;
+CYCLE: while ($frame ne '') {
+    $frame =~ /[|](\w*)$/
+        or die "when cycling, frame is nonempty but has no bar";
+    my $commandlist = $1;
+    $commandlist eq '' and $explicit = 1;
+    $explicit and $frame =~ s/[|](\w*)$//;
+    $explicit = 0;
+    unshift @commandlist, split /([0-57]*)/, $commandlist;
+    while (@commandlist) {
+        if ($delayed_frame_copy != 1) {
+            $frame =~ s/[|]\K(\w*)$/$1 x $delayed_frame_copy/e
+                || die "Attempt to read input with no bar in the frame";
+            $delayed_frame_copy = 1;
+        }
+        $debug and print STDERR "\t$frame ", @commandlist, "\n";
+        my $command = shift @commandlist;
+        length $command or next;
+        for ($command) {
+            /[0-57]/ and $frame .= $command =~ y/0-57/67cegr|/r;
+            /6/ and $frame =~ s/[|](\w*)$/pacify $1/e
+                || die "6 command run with no bar in the frame";
+            /c/ and $frame =~ s/[|](\w*)$/|$1|$1/
+                || die "'copy' command run with no bar in the frame";
+            /e/ and $frame =~ s/[|]\w*[|](\w*)$/(oprint $1), ""/e
+                ||  $frame =~ s/(\w*)$/         (oprint $1), exit/e;
+            /g/ and $frame =~ s/(\w*)[|](\w*)$/$2||$1/
+                || die "'grab' command run with no bar in the frame";
+            /r/ and $explicit = 1 and next CYCLE;
+        }
+    }
+}
+
+$pending_octal =~ s/1+$//;
+if (length $pending_octal) {
+    $pending_octal .= 1 until length $pending_octal == $bits_per_byte;
+    print chr oct "0b$pending_octal";
+}