ppencode

ppencode is

1. a subset of Perl who restricts source code to have only Perl keywords, defined by Yoshino TAKESAKO in 2005,
2. a Perl program to generate a ppencode program that outputs a given string or an encoding method to represent a text with ppencode program written by Yoshino TAKESAKO in 2005, and,
3. a translator to convert arbitrary Perl program into ppencode program designed and published by Shinjiro Hamaji in 2015, which is also known as ppencode 2.

Origin

In September 2003 the PerlMonk user blockhead had posted a thread Fun With Reserved Keywords, along with the following Perl program:

not exp log srand xor s qq qx xor
s x x length uc ord and print chr
ord for qw q join use sub tied qx
xor eval xor print qq q q xor int
eval lc q m cos and print chr ord
for qw y abs ne open tied hex exp
ref y m xor scalar srand print qq
q q xor int eval lc qq y sqrt cos
and print chr ord for qw x printf
each return local x y or print qq
s s and eval q s undef or oct xor
time xor ref print chr int ord lc
foreach qw y hex alarm chdir kill
exec return y s gt sin sort split

This is a program to output the string "just another perl hacker". Blockhead excessed that this program works without punctuation.

Definition of Perl keywords

TAKESAKO defined syntax keywords, operators, and builtin functions who have lowercased alphabets only to be Perl keyword for ppencode; in other words, these are valid 38+182=220 ppencode tokens:

lt gt le ge eq ne cmp not and or xor if else elsif while for foreach continue goto last local map
my next redo require return use tr y s m q qq qr qw qx x

abs accept alarm bind binmode bless caller chdir chmod chomp chop chown chr chroot
close closedir connect cos crypt dbmclose dbmopen defined delete die do dump each eof eval
exec exists exit exp fcntl fileno flock fork formline getc getlogin getpeername getpgrp getppid
getpriority getpwnam getgrnam gethostbyname getnetbyname getprotobyname getpwuid
getgrgid getservbyname gethostbyaddr getnetbyaddr getprotobynumber getservbyport
getpwent getgrent gethostent getnetent getprotoent getservent setpwent setgrent sethostent
setnetent setprotoent setservent endpwent endgrent endhostent endnetent endprotoent
endservent getsockname getsockopt glob gmtime grep hex import index int ioctl join keys kill
lc lcfirst length link listen localtime log lstat mkdir msgctl msgget msgrcv msgsnd no oct open
opendir ord pack pipe pop pos print printf push quotemeta rand read readdir readlink recv ref
rename reset reverse rewinddir rindex rmdir scalar seek seekdir select semctl semget semop
send setpgrp setpriority setsockopt shift shmctl shmget shmread shmwrite shutdown sin sleep
socket socketpair sort splice split sprintf sqrt srand stat study substr symlink syscall sysread
system syswrite tell telldir tie time times truncate uc ucfirst umask undef unlink unpack untie
unshift utime values vec wait waitpid wantarray warn write

You may notice that atan2, a builtin function, is not in; this is because it has a digit, which is invalid for ppencode.

On the other hand, shinh, the author of ppencode 2, defines keywords shall be 248. Here are new 28 tokens:

atan break default elseif evalbytes fc flags format given lock order our package precision
prototype readline readpipe say size state sub sysopen sysseek tied unless until vector when

However, the following six tokens are not built in Perl 5.34.0.

atan flags order precision size vector

Additionally, these eight tokens are not available unless specified features are enable:

break default evalbytes fc given say state when

Syntax

It is not explicitly defined, but TAKESAKO's ppencode outputs the program as in following syntax:

program = *EMPTY* | "#!/usr/bin/perl -w\n" keywords " "
keywords = keyword | keywords " " keyword 

The program generated by ppencode 2 is represented by as follows:

program = keyword | program " " keyword

It is common that

1. a ppencode program shall have only a line, and
2. a ppencode program is represented as a sequence of keywords, delimitated by exactly one space character (which is 0x20 in ascii).

So this article convertly follows the syntax.

Detailed syntax

Since this is Perl without punctuation, a ppencode program is equivalent to a Perl program with just one statement:

Program := Statement
Statement := WithModifier | SimpleStatement
WithModifier := WithIf | WithUnless | WithWhile | WithUntil | WithFor
SimpleStatement := Expression
WithIf := Expression Ws IfKeyword Ws Expression
WithUnless := Expression Ws UnlessKeyword Ws Expression
WithWhile := Expression Ws WhileKeyword Ws Expression
WithUntil := Expression Ws UntilKeyword Ws Expression
WithFor := Expression Ws ForKeyword Ws ListExpression

Tricks

ppencode

Here is an example output of input "Hi" to the ppencode script, conveniently inserting line-breaks and comments:

# a dummy
# each function is separated by a keyword "and" instead of semicolon
length q pop and
# prints 'H'
# "q chr lc" equals "hr l" in Perl
# "chr ord" is used to get the first character of a string
print chr ord uc q chr lc and
# prints 'i'
print chr ord q tie lt 

Here is an example output against input "=":

length q my m and
# since "=" is not an alphabet, it must be generated from several functions
print chr oct oct ord q eq ge 

Here is an example to output "あ" in shift-jis encode (i.e. 0x82 0xa0):

length q chdir exec and
# ord uc q qr q: 82
# hex 82: 130
# chr 130: "\x82"
print chr hex ord uc q qr q and
# length q q ... q: 160
# chr 160: "\xa0"
print chr length q q setservent symlink eof gethostent rename join getprotobyname time getpwuid waitpid dbmopen getgrgid printf getpwnam getgrgid getsockopt socket rename send ref q 

ppencode 2

The overall of generated program is:

# generate a string to be evaluated:
# '$_="";eval "vxxx.xxx.xxx.xxx"', where vxxx.xxx.xxx.xxx is version number
# eval it

It is a point that xor is used instead of ;, because unlike and and or, it always evaluate both operands from left to right.

External Resources

• ppencode in JavaScript (from the Wayback Machine; retrieved on 14 November 2005)
• ppencode in Perl (from the Wayback Machine; retrieved on 15 December 2005)
• ppencode 2
• Result by a language - Perl results in Anarchy Golf. Some posts with "alpha" in user name meets the syntax of the ppencode language.

See also

• Perl