Execute prints backwards

Question

Your task is to reverse the order in which some prints get executed.

---

Specs:
Your code will be in this form:

//some lines of code
/*code*/ print "Line1" /*code*/
/*code*/ print "Line2" /*code*/
/*code*/ print "Line3" /*code*/
/*code*/ print "Line4" /*code*/
//some lines of code

You will have to print (or echo, or write, or equivalent) those strings from the fourth to the first.

• You decide which lines of your program must print the strings, but they must be adjacent;

• Every line can contain only one print, and cannot exceed 60 bytes in length;

• Since this is popularity-contest, be creative and avoid to write just a goto or a simple for(i){if(i=4)print"Line1";if(i=3)...}

• The most upvoted answer in 2 weeks wins this.

• Your output MUST be Line4 Line3 Line2 Line1 OR Line4Line3Line2Line1 OR Line4\nLine3\nLine2\nLine1(where \n is a newline), and it must be generated only by executing those prints backwards.

Happy coding!

UPDATE: Contest is over! Thank you all :)

Answer 1

SQL

(mySQL 5.6)

SELECT 'Line1' UNION
SELECT 'Line2' UNION
SELECT 'Line3' UNION
SELECT 'Line4' 
ORDER BY Line1 DESC;

If you count SELECTing a literal as equivalent to a print statement anyway.

mySQL defaults to including the column name and adding fancy table formatting, but if you're at the cli they can be turned off if you do something like:

mysql --skip-column-names -B -e "SELECT 'Line1' ... etc ...;"

Output:

Line4
Line3
Line2
Line1

Answer 2

C#

Switching the console output to a MemoryStream and modifying that before dumping to screen

void Main()
{
    var stream = new MemoryStream();
    using (var writer = new StreamWriter(stream))
    {
        var defaultOut = Console.Out;

        // change the console output to the in-memory writer
        Console.SetOut(writer);

        Console.WriteLine("line1");
        Console.WriteLine("line2");
        Console.WriteLine("line3");
        Console.WriteLine("line4");

        // reset the console output to the default
        Console.SetOut(defaultOut);
    }

    // write the contents of the MemoryStream to screen whilst tweaking the output
    Console.Write(stream.ToArray().Select(SwitchChar).ToArray());
}

public char SwitchChar(byte b)
{
    var c = (char)b;
    switch (c)
    {
        case '1': return '4';
        case '2': return '3';
        case '3': return '2';
        case '4': return '1';
        default: return c;
    }
}

Answer 3

Kinda lame, but I think it works. C-like languages.

main()
{
    switch(4)
    {
    case 1: print(1); goto 5; break;
    case 2: print(2); goto 1; break;
    case 3: print(3); goto 2; break;
    case 4: print(4); goto 3; break;
    case 5: break;
    }
}

Answer 4

Batch

@echo off
cls
goto d
:a
echo 'line1' & goto e
:b
echo 'line2' & goto a
:c
echo 'line3' & goto b
:d
echo 'line4' & goto c
:e
pause>nul

Quite frankly the best I could do...

Answer 5

RProgN

1 print
2 print
3 print
4 print

Output

4
3
2
1

Print doesn't actually exist in RProgN, it's actually titled just 'p'. This just appends 1 through 4 to the stack, then RProgN implicitly prints the stack from top to bottom, which gives the desired result.

Answer 6

Perl

At last a use for eval:

eval(join("", reverse <<"HERE"
print "Line 1\n";
print "Line 2\n";
print "Line 3\n";
print "Line 4\n";
HERE
))

Answer 7

Perl

eval for reverse <DATA>
__DATA__
print "Line 1\n"
print "Line 2\n"
print "Line 3\n"
print "Line 4\n"

More or less an equivalent of my Postscript answer (though I like it less because of reverse. Stack-based Postscript is beautiful there, if you excuse me praising my own answer)

Answer 8

Mathematica

Unprotect[Line];
Line = "Line4";
Line i_ ^:= "Line" <> ToString[5 - i]
Print[Line 1]
Print[Line 2]
Print[Line 3]
Print[Line 4]

Answer 9

JavaScript

' \
    print "Line1" \
    print "Line2" \
    print "Line3" \
    print "Line4" \
'.replace(/["\s\\]/g,"").split("print").reverse().map(function(line){if(line)console.log(line)});

Print() means print(er) so outputs to console instead.

Answer 10

Perl

Those pretty lines

map+$_->(),reverse
sub{print"Line1"},
sub{print"Line2"},
sub{print"Line3"},
sub{print"Line4"};

Answer 11

Python 3

class Printer(object):
    def __init__(self):
        self.buffer = []

    def print(self, text):
        self.buffer.append(text)

        if len(self.buffer) == 4:
            while self.buffer:
                print(self.buffer.pop())

printer = Printer()

printer.print('Line 1')
printer.print('Line 2')
printer.print('Line 3')
printer.print('Line 4')

Answer 12

K

K is evaluated right to left

(
  -1@"line 1";
  -1@"line 2";
  -1@"line 3";
  -1@"line 4"
  );

.

$ q a.k -q
line 4
line 3
line 2
line 1

Answer 13

C#

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

class Program
{
    static void Main()
    {
        Console.SetOut(new BackwardsWriter());

        Console.WriteLine("Line 1");
        Console.WriteLine("Line 2");
        Console.WriteLine("Line 3");
        Console.WriteLine("Line 4");
    }
}

class BackwardsWriter : TextWriter
{
    private readonly TextWriter console = Console.Out;
    private readonly IList<string> lines = new List<string>();

    public override void WriteLine(string value)
    {
        lines.Add(value);
    }

    public override Encoding Encoding
    {
        get { return console.Encoding; }
    }

    ~BackwardsWriter()
    {
        foreach (var line in lines.Reverse())
        {
            console.WriteLine(line);
        }
    }
}

Note that this may not actually work (objects are not required to be finalized in C#), but it does work for me in VS 2012.

Answer 14

Perl

there is more than one way to do it!

package MagicHandle;
require Tie::Handle;
our @ISA = qw(Tie::Handle);
my @data = ();
sub TIEHANDLE { my $i; bless \$i, shift }
sub PRINT { shift @_; push @data, @_ }
sub UNTIE { print reverse @data }

package main;
tie *fh, 'MagicHandle'; 
select *fh;

print "one";
print "two";
print "three";
print "four";

select STDOUT; 
untie *fh;

Answer 15

PHP

Why use eval when you have data wrappers?

<?die(include('data:text/plaintext;base64,'.base64_encode(implode(PHP_EOL,array_slice(array_reverse(file(__FILE__)),0,4)))));?>
Line 1
Line 2
Line 3
Line 4

For this to work you must be running PHP 5.2 or greater and both allow_url_fopen and allow_url_include must be set to "On" in your php.ini file.

Answer 16

Python 3.3

print('Line 1') if not \
(print('Line 2') if not \
(print('Line 3') if not \
print('Line 4') else None) else None) else None

Answer 17

JavaScript

Because of the nature of this problem; it is best that we use scalable asynchronous code.

var config = {
    maxLines: 4,
};

print.lines = 0;
function print() {
    // Error checking
    if (++print.lines > config.maxLines) throw new Error('T_PAAMAYIM_NEKUDOTAYIM');

    // TODO: Implement Promises
    window.setTimeout(
        console.log.apply.bind.apply(
            console.log.apply, [
                console.log,
                console,
                arguments
            ]
        ),
    config.maxLines + 4 - print.lines);
}


print('Line 1');
print('Line 2');
print('Line 3');
print('Line 4');

Answer 18

Matlab: something different

s = {'print ' 'Line1'...
     'print ' 'Line2'...
     'print ' 'Line3'...
     'print ' 'Line4'};

[s{end:-2:2}]

Obfuscation attempted

Answer 19

SQL

I felt a little left out no one tackled this with SQL.

declare @oldsql varchar(max)
declare @newSQL varchar(max)
declare @findvar varchar(7)
declare @replaceVar varchar(20)
declare @varLength int
declare @sqlLength int

set @findvar = '%print%'
set @varLength = len(@findvar) - 3

set @oldsql = 
        ' print ''Line1''' + 
        ' print ''Line2''' + 
        ' print ''Line3''' + 
        ' print ''Line4''' 

set @sqlLength = len(@oldsql)

SET @newSQL = (
    SELECT SUBSTRING(@oldsql 
            ,@sqlLength - PATINDEX(reverse(@findvar)
            ,REVERSE(@oldsql)) - @varLength
            ,LEN(@oldsql)))
SET @replaceVar = 
    RIGHT(@oldsql
        ,PATINDEX(reverse(@findvar)
        ,REVERSE(@oldsql))+@varLength)
SET @oldSql = 
    RTRIM(REPLACE(@oldSQL
        , REPLACE(@replaceVar,'','''')
        ,''))
SET @sqlLength = LEN(@oldsql)

SET @newSQL = @newSQL +  (
    SELECT SUBSTRING(@oldsql 
            ,@sqlLength - PATINDEX(reverse(@findvar)
            ,REVERSE(@oldsql)) - @varLength
            ,LEN(@oldsql)))
SET @replaceVar = 
    RIGHT(@oldsql
        ,PATINDEX(reverse(@findvar)
        ,REVERSE(@oldsql))+@varLength)
SET @oldSql = 
    RTRIM(REPLACE(@oldSQL
        , REPLACE(@replaceVar,'','''')
        ,''))
SET @sqlLength = LEN(@oldsql)

SET @newSQL = @newSQL +  (
    SELECT SUBSTRING(@oldsql 
            ,@sqlLength - PATINDEX(reverse(@findvar)
            ,REVERSE(@oldsql)) - @varLength
            ,LEN(@oldsql)))


SET @replaceVar = 
    RIGHT(@oldsql
        ,PATINDEX(reverse(@findvar)
        ,REVERSE(@oldsql))+@varLength)
SET @oldSql = 
    RTRIM(REPLACE(@oldSQL
        , REPLACE(@replaceVar,'','''')
        ,''))
SET @sqlLength = LEN(@oldsql)

SET @newSQL = @newSQL +  (
    SELECT SUBSTRING(@oldsql 
            ,@sqlLength - PATINDEX(reverse(@findvar)
            ,REVERSE(@oldsql)) - @varLength
            ,LEN(@oldsql)))
exec (@newSQL)

Answer 20

Rebol

use [p][p: :print  print: func [s n [any-type!]][p s]]
print {Line1}
print {Line2}
print {Line3}
print {Line4}

Normally 'print only takes 1 argument, but we're redefining it to take 2 - the second of which is the next call to `print, which must be evaluated first to get a return value.

Except because it accepts [any-type!], the second argument is optional - hence not needing an extra arg for the last call.

Answer 21

Python3

def print(x,p=
print):p(x[:-1]+str(5-int(x[-1])))
print("line1")
print("line2")
print("line3")
print("line4")

Answer 22

Python3

print('line1') if not (
print('line2') if not (
print('line3') if not 
print('line4') else 
0) else 0) else 0

Answer 23

My version in batch - using "batch file reflection" ;)

This one actually supports up to 9 statements to be executed backwards (but can easily be expanded to support more), and they could be almost any kind of commands - not just print statements!

The only rules are that the statements which you want to run reversed must appear in the file between the "rem BEGIN_REV" and "rem END_REV" comments, and that the file name you run it as must end in .BAT (not .CMD!).

@echo off
setlocal enabledelayedexpansion

set ffrag=FILEFRAG%random%

call :run %0
goto :eof

rem BEGIN_REV
echo Line1
echo Line2
echo Line3
echo Line4
rem END_REV

:run

set me=%1
set me=%me:.bat=%.bat
set /a isOn=0
set /a incrCount=0

for /f "tokens=*" %%i in (%me%) do (
    set ln=
    set ln=%%i

    if !isOn!==0 (
        set d=
        set d=!ln:begin_rev=!

        if not !d!==!ln! (
            rem Starting block
            set /a isOn=1
        )
    ) else (
        rem Inside block

        set /a incrCount=!incrCount!+1
        echo !ln! > %ffrag%_!incrCount!.b

        set d=
        set d=!ln:END_REV=!

        if not !d!==!ln! (
            rem End of block reached
            goto :endloop
        )
    )
)

:endloop

del %ffrag%_%incrCount%.b

for /f %%i in ('dir /s/b/O:-N %ffrag%*') do (
    type %%i >> %ffrag%_FINAL.bat
)

del %ffrag%*.b
call %ffrag%_FINAL.bat
del %ffrag%_FINAL.bat

Output:

Line4
Line3
Line2
Line1

Answer 24

Scala

object PrintRev extends App{
    val rev : (=>Unit,=>Unit,=>Unit,=>Unit) => Unit = (v1,v2,v3,v4) => {v4;v3;v2;v1}
    rev(println("Line1"),
      println("Line2"),
      println("Line3"),
      println("Line4"))
}

Answer 25

Coffeescript

This one is using coffeescript, by overriding the console.log function to skip the undefined second argument.

c = window.console
console =
  log: () ->
    c.log arguments[0]
    c.log arguments[1] if arguments[1]
console.log "Line1", 
console.log "Line2", 
console.log "Line3", 
console.log "Line4"

Answer 26

Perl

eval ($_) for (   reverse split("\n", <<EOF
print "Line1"; 
print "Line2"; 
print "Line3"; 
print "Line4";
EOF
) );

Very simple perl-Example with eval...

Answer 27

Python

there's my code :)

import sys
old_stdout = sys.stdout
sys.stdout = open('file.txt', 'w')

print 'Line 1'
print 'Line 2'
print 'Line 3'
print 'Line 4'

sys.stdout = old_stdout

a = open('file.txt','r').read().splitlines()
a.sort(reverse=True)

print '\n'.join(a)

Answer 28

Python 2.7 (may work down to 2.4)

Tested with CPython 2.7.5 and PyPy 2.0.2

def inv(fn):
    import types
    t=fn.__code__
    c=list(t.co_code)
    idxs=[i+1 for i,j in enumerate(c) if j=='d' and c[i+1]!='\0']
    for i in range(len(idxs)/2):
        c[idxs[i]], c[idxs[-i-1]] = c[idxs[-i-1]], c[idxs[i]]
    outcode=types.CodeType( t.co_argcount, t.co_nlocals, t.co_stacksize, t.co_flags, ''.join(c), t.co_consts, t.co_names, t.co_varnames, t.co_filename, t.co_name, t.co_firstlineno, t.co_lnotab)
    return types.FunctionType(outcode, globals(), fn.__name__[::-1])

@inv
def f():
    print 'Line1'
    print 'Line2'
    print 'Line3'
    print 'Line4'

f()

http://ideone.com/A2AJ2s

A somewhat more secure approach requires changing the inv function to something like this:

def inv(fn):
    import types
    import dis

    t=fn.__code__
    c=list(t.co_code)

    idxs=[]
    i=0
    n=len(c)
    lc=dis.opmap['LOAD_CONST']

    while i<n:
        opcode=ord(c[i])
        if opcode==lc and c[i+1]!='\0':
            idxs+=[i+1]
        i+=1
        if opcode>=dis.HAVE_ARGUMENT:
            i+=2

    for i in range(len(idxs)/2):
        c[idxs[i]], c[idxs[-i-1]] = c[idxs[-i-1]], c[idxs[i]]
    outcode=types.CodeType( t.co_argcount, t.co_nlocals, t.co_stacksize, t.co_flags, ''.join(c), t.co_consts, t.co_names, t.co_varnames, t.co_filename, t.co_name, t.co_firstlineno, t.co_lnotab)
    return types.FunctionType(outcode, globals(), fn.__name__[::-1])

http://ideone.com/8WgMxk

Answer 29

Haskell

import Prelude (print, return, (>>=))

main = do
   print "Line 1"
   print "Line 2"
   print "Line 3"
   print "Line 4"

a>>b=b>>= \_->a

Run with

$ runhaskell -XRebindableSyntax reversed.hs

(Note that without the RebindableSyntax flag, it's still a valid Haskell program and will print in the normal order)

---

Standard Haskell98 alternative:

import Prelude hiding (print)

main = r$do
   print "Line 1"
   print "Line 2"
   print "Line 3"
   print "Line 4"

data R a=R{r::IO a}
instance Monad R where R a>>=b=R$r(b u)>>= \_->fmap u a;return=R .return
print=R .putStrLn
u::u;u=u

Answer 30

C#

Kind of lame, just my two cents:

var printMeReverse = new List<Action> {
    new Action(() => Console.WriteLine ("Line1")),
    new Action(() => Console.WriteLine ("Line2")),
    new Action(() => Console.WriteLine ("Line3")),
    new Action(() => Console.WriteLine ("Line4"))
};
printMeReverse.Reverse();
printMeReverse.ForEach(a => a.Invoke());