I reverse the source code, you reverse the input!

Question

Yet another blatant rip-off of a rip-off of a rip-off. Go upvote those!

Your task, if you wish to accept it, is to write a program/function that outputs/returns its string input/argument. The tricky part is that if I reverse your source code, the output must be reversed too.

For simplicity, you can assume that the input is always a single line string containing only ASCII letters (a-z), digits (0-9) and spaces.

Should support an input of at least 8 characters long (longer than 8 is not necessary).

Behaviour for empty input is undefined.

Examples

Let's say your source code is ABC and its input is xyz. If I write CBA instead and run it, the output must be zyx.

Let's say your source code is ABC and its input is 96. If I write CBA instead and run it, the output must be 69.

A single leading or trailing white-space is acceptable as long as it is consistent in both normal and reversed outputs.

Answer 1

JavaScript, 32 bytes

s=>s//``nioj.)(esrever.]s...[>=s

Reversed:

s=>[...s].reverse().join``//s>=s

Answer 2

APL (Dyalog Unicode), 3 2 bytes^SBCS

-1 byte thanks to dzaima

⌽⊂

Try it online!

⊂ enclose the argument to treat it as a singleton: [1,2,3] → [[1,2,3]]

⌽ reverse (has no effect on singletons): [[1,2,3]] → [[1,2,3]]

An enclosed array prints with a leading an a trailing space.

!enilno ti yrT

⌽ reverse (has no effect on singletons): [1,2,3] → [3,2,1]

⊂ enclose: [1,2,3] → [[1,2,3]]

An enclosed array prints with a leading an a trailing space.

Answer 3

Bash, 9 bytes

cat # ver

Reversed:

rev # tac

Try it online! !enilno ti yrT

Answer 4

Keg, 3 2 bytes

#?

Try it online! or !enilno ti yrT

Explained

#? #Implicit cat
?# Reversed input

Heh. That's right. Keg can stand up to those 2-byte answers too (and using pure, plain ASCII)!

Old Program

^#?

Try it online! Or !enilno ti yrT

Because two can play the 3-byte game. That's why. (did I mention that's 3 bytes of utf8 ASCII?)

^#? #Reverse an empty stack, taking implicit input

?#^ #take input

Answer 5

Ruby, 21 bytes

->x{x}#}esrever.x{x>-

Try it online!

->x{x.reverse}#}x{x>-

!enilno ti yrT

Answer 6

Haskell, 11 bytes

id--esrever

Try it online! Try it reversed!

Answer 7

Charcoal, 2 bytes

Ｓ←

Try it online! Explanation: Ｓ implicitly prints the explicit input and ← moves the cursor left (no effect on the final output). Reversed:

←Ｓ

Try it online! ← changes the direction of the implicit print of the explicit input Ｓ thus reversing the output.

Answer 8

Stack Cats -m, 4 bytes

|>I|

Try it online!

Try it reversed!

This works for any inputs that don't contain null bytes.

Explanation

Wow, I've reached the point where I'm writing these by hand...

The full program is |>I|I<|.

|   Reverse the entire stack down to the EOF marker -1 (since there are no zeros in the input).
>   Move one stack over to the right (which only contains zeros).
I   Does nothing on zero.
|   Does nothing on zero.
I   Does nothing on zero.
<   Move back to the initial stack.
|   Reverse the input once more.

As in the solution to the previous challenge, since the centre command | does nothing, so does the entire program.

The reversed program is then |I>|<I|.

|   Reverse the entire stack down to the EOF marker -1 (since there are no zeros in the input).
I   Move the -1 one stack to the left and turn it into a +1.
>   Move back to the initial stack.
|   Reverse it again, but this time without the EOF marker.
<   Move back to the left.
I   Move the +1 back onto the initial stack and turn it into a -1 again.
|   Reverse the entire stack. We now have the -1 as an EOF marker again at the bottom
    and the rest of the stack has been reversed three times, i.e. one net reversal.

Interestingly, if we use this reversing program without -m we still get a working solution this time, so the only additional bytes incurred by omitting -m are those we get from mirroring the code.

---

Stack Cats, 7 bytes

|I<|>I|

Try it online!

Try it reversed!

Explanation

The reversed version of this program is |I>|<I|, the same as above so we can ignore that. But the non-reversed version differs. Since the <> now point the other way, the centre command ends up doing nothing, so the program becomes a cat:

|   Reverse the entire stack down to the EOF marker -1 (since there are no zeros in the input).
I   Move the -1 one stack to the left and turn it into a +1.
<   Move another stack to the left, which contains only zeros.
|   Does nothing on zero.

And thus, >I| exactly undo the first half of the program.

Answer 9

05AB1E, 2 bytes

RI

Try it online or try it online reversed.

Explanation:

R   # Reverse the (implicit) input
 I  # Push the input
    # (output the top of the stack implicitly as result)

I   # Push the input
 R  # Reverse it
    # (output the top of the stack implicitly as result)

Answer 10

Python 3, 27 bytes

lambda s:s#]1-::[s:s adbmal

Try it online!

!enilno ti yrT

Answer 11

Turing Machine Language, 14324 14321 bytes

0 ( ( l 6 ;
0 * * l 2 ;
1 _ _ l 2 ;
2 _ ( r 3 ;
3 _ _ r 4 ;
4 _ _ l 3) ;
4 * * r 2 ;
3) _ ) l 5 ;
3 * * r 3 ;
5 ( ( * 0 ;
5 * * l 5 ;
6 _ _ l 7 ;
7 _ ] r 8 ;
8 ) ) l 9 ;
8 * * r 8 ;
9 0 @ l c0 ;
9 1 @ l c1 ;
9 2 @ l c2 ;
9 3 @ l c3 ;
9 4 @ l c4 ;
9 5 @ l c5 ;
9 6 @ l c6 ;
9 7 @ l c7 ;
9 8 @ l c8 ;
9 9 @ l c9 ;
9 a @ l a ;
9 A @ l A ;
9 b @ l b ;
9 B @ l B ;
9 c @ l c ;
9 C @ l C ;
9 d @ l d ;
9 D @ l D ;
9 e @ l e ;
9 E @ l E ;
9 f @ l f ;
9 F @ l F ;
9 g @ l g ;
9 G @ l G ;
9 h @ l h ;
9 H @ l H ;
9 i @ l i ;
9 I @ l I ;
9 j @ l j ;
9 J @ l J ;
9 k @ l k ;
9 K @ l K ;
9 l @ l l ;
9 L @ l L ;
9 m @ l m ;
9 M @ l M ;
9 n @ l n ;
9 N @ l N ;
9 o @ l o ;
9 O @ l O ;
9 p @ l p ;
9 P @ l P ;
9 q @ l q ;
9 Q @ l Q ;
9 r @ l r ;
9 R @ l R ;
9 s @ l s ;
9 S @ l S ;
9 t @ l t ;
9 T @ l T ;
9 u @ l u ;
9 U @ l U ;
9 v @ l v ;
9 V @ l V ;
9 w @ l w ;
9 W @ l W ;
9 x @ l x ;
9 X @ l X ;
9 y @ l y ;
9 Y @ l Y ;
9 z @ l z ;
9 Z @ l Z ;
c0 ] ] l c0a ;
c0 * * l c0 ;
c0a _ 0 r @0 ;
c0a * * l c0a ;
@0 @ 0 l nC ;
@0 * * r @0 ;
c1 ] ] l c1a ;
c1 * * l c1 ;
c1a _ 1 r @1 ;
c1a * * l c1a ;
@1 @ 1 l nC ;
@1 * * r @1 ;
c2 ] ] l c2a ;
c2 * * l c2 ;
c2a _ 2 r @2 ;
c2a * * l c2a ;
@2 @ 2 l nC ;
@2 * * r @2 ;
c3 ] ] l c3a ;
c3 * * l c3 ;
c3a _ 3 r @3 ;
c3a * * l c3a ;
@3 @ 3 l nC ;
@3 * * r @3 ;
c4 ] ] l c4a ;
c4 * * l c4 ;
c4a _ 4 r @4 ;
c4a * * l c4a ;
@4 @ 4 l nC ;
@4 * * r @4 ;
c5 ] ] l c5a ;
c5 * * l c5 ;
c5a _ 5 r @5 ;
c5a * * l c5a ;
@5 @ 5 l nC ;
@5 * * r @5 ;
c6 ] ] l c6a ;
c6 * * l c6 ;
c6a _ 6 r @6 ;
c6a * * l c6a ;
@6 @ 6 l nC ;
@6 * * r @6 ;
c7 ] ] l c7a ;
c7 * * l c7 ;
c7a _ 7 r @7 ;
c7a * * l c7a ;
@7 @ 7 l nC ;
@7 * * r @7 ;
c8 ] ] l c8a ;
c8 * * l c8 ;
c8a _ 8 r @8 ;
c8a * * l c8a ;
@8 @ 8 l nC ;
@8 * * r @8 ;
c9 ] ] l c9a ;
c9 * * l c9 ;
c9a _ 9 r @9 ;
c9a * * l c9a ;
@9 @ 9 l nC ;
@9 * * r @9 ;
a ] ] l aa ;
a * * l a ;
aa _ a r @a ;
aa * * l aa ;
@a @ a l nC ;
@a * * r @a ;
A ] ] l Aa ;
A * * l A ;
Aa _ A r @A ;
Aa * * l Aa ;
@A @ A l nC ;
@A * * r @A ;
b ] ] l ba ;
b * * l b ;
ba _ b r @b ;
ba * * l ba ;
@b @ b l nC ;
@b * * r @b ;
B ] ] l Ba ;
B * * l B ;
Ba _ B r @B ;
Ba * * l Ba ;
@B @ B l nC ;
@B * * r @B ;
c ] ] l ca ;
c * * l c ;
ca _ c r @c ;
ca * * l ca ;
@c @ c l nC ;
@c * * r @c ;
C ] ] l Ca ;
C * * l C ;
Ca _ C r @C ;
Ca * * l Ca ;
@C @ C l nC ;
@C * * r @C ;
d ] ] l da ;
d * * l d ;
da _ d r @d ;
da * * l da ;
@d @ d l nC ;
@d * * r @d ;
D ] ] l Da ;
D * * l D ;
Da _ D r @D ;
Da * * l Da ;
@D @ D l nC ;
@D * * r @D ;
e ] ] l ea ;
e * * l e ;
ea _ e r @e ;
ea * * l ea ;
@e @ e l nC ;
@e * * r @e ;
E ] ] l Ea ;
E * * l E ;
Ea _ E r @E ;
Ea * * l Ea ;
@E @ E l nC ;
@E * * r @E ;
f ] ] l fa ;
f * * l f ;
fa _ f r @f ;
fa * * l fa ;
@f @ f l nC ;
@f * * r @f ;
F ] ] l Fa ;
F * * l F ;
Fa _ F r @F ;
Fa * * l Fa ;
@F @ F l nC ;
@F * * r @F ;
g ] ] l ga ;
g * * l g ;
ga _ g r @g ;
ga * * l ga ;
@g @ g l nC ;
@g * * r @g ;
G ] ] l Ga ;
G * * l G ;
Ga _ G r @G ;
Ga * * l Ga ;
@G @ G l nC ;
@G * * r @G ;
h ] ] l ha ;
h * * l h ;
ha _ h r @h ;
ha * * l ha ;
@h @ h l nC ;
@h * * r @h ;
H ] ] l Ha ;
H * * l H ;
Ha _ H r @H ;
Ha * * l Ha ;
@H @ H l nC ;
@H * * r @H ;
i ] ] l ia ;
i * * l i ;
ia _ i r @i ;
ia * * l ia ;
@i @ i l nC ;
@i * * r @i ;
I ] ] l Ia ;
I * * l I ;
Ia _ I r @I ;
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j ] ] l ja ;
j * * l j ;
ja _ j r @j ;
ja * * l ja ;
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J ] ] l Ja ;
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Ja _ J r @J ;
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k ] ] l ka ;
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ka * * l ka ;
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K ] ] l Ka ;
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Ka _ K r @K ;
Ka * * l Ka ;
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l ] ] l la ;
l * * l l ;
la _ l r @l ;
la * * l la ;
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L ] ] l La ;
L * * l L ;
La _ L r @L ;
La * * l La ;
@L @ L l nC ;
@L * * r @L ;
m ] ] l ma ;
m * * l m ;
ma _ m r @m ;
ma * * l ma ;
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@m * * r @m ;
M ] ] l Ma ;
M * * l M ;
Ma _ M r @M ;
Ma * * l Ma ;
@M @ M l nC ;
@M * * r @M ;
n ] ] l na ;
n * * l n ;
na _ n r @n ;
na * * l na ;
@n @ n l nC ;
@n * * r @n ;
N ] ] l Na ;
N * * l N ;
Na _ N r @N ;
Na * * l Na ;
@N @ N l nC ;
@N * * r @N ;
o ] ] l oa ;
o * * l o ;
oa _ o r @o ;
oa * * l oa ;
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@o * * r @o ;
O ] ] l Oa ;
O * * l O ;
Oa _ O r @O ;
Oa * * l Oa ;
@O @ O l nC ;
@O * * r @O ;
p ] ] l pa ;
p * * l p ;
pa _ p r @p ;
pa * * l pa ;
@p @ p l nC ;
@p * * r @p ;
P ] ] l Pa ;
P * * l P ;
Pa _ P r @P ;
Pa * * l Pa ;
@P @ P l nC ;
@P * * r @P ;
q ] ] l qa ;
q * * l q ;
qa _ q r @q ;
qa * * l qa ;
@q @ q l nC ;
@q * * r @q ;
Q ] ] l Qa ;
Q * * l Q ;
Qa _ Q r @Q ;
Qa * * l Qa ;
@Q @ Q l nC ;
@Q * * r @Q ;
r ] ] l ra ;
r * * l r ;
ra _ r r @r ;
ra * * l ra ;
@r @ r l nC ;
@r * * r @r ;
R ] ] l Ra ;
R * * l R ;
Ra _ R r @R ;
Ra * * l Ra ;
@R @ R l nC ;
@R * * r @R ;
s ] ] l sa ;
s * * l s ;
sa _ s r @s ;
sa * * l sa ;
@s @ s l nC ;
@s * * r @s ;
S ] ] l Sa ;
S * * l S ;
Sa _ S r @S ;
Sa * * l Sa ;
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@S * * r @S ;
t ] ] l ta ;
t * * l t ;
ta _ t r @t ;
ta * * l ta ;
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@t * * r @t ;
T ] ] l Ta ;
T * * l T ;
Ta _ T r @T ;
Ta * * l Ta ;
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u ] ] l ua ;
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U ] ] l Ua ;
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v ] ] l va ;
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va _ v r @v ;
va * * l va ;
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@v * * r @v ;
V ] ] l Va ;
V * * l V ;
Va _ V r @V ;
Va * * l Va ;
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w ] ] l wa ;
w * * l w ;
wa _ w r @w ;
wa * * l wa ;
@w @ w l nC ;
@w * * r @w ;
W ] ] l Wa ;
W * * l W ;
Wa _ W r @W ;
Wa * * l Wa ;
@W @ W l nC ;
@W * * r @W ;
x ] ] l xa ;
x * * l x ;
xa _ x r @x ;
xa * * l xa ;
@x @ x l nC ;
@x * * r @x ;
X ] ] l Xa ;
X * * l X ;
Xa _ X r @X ;
Xa * * l Xa ;
@X @ X l nC ;
@X * * r @X ;
y ] ] l ya ;
y * * l y ;
ya _ y r @y ;
ya * * l ya ;
@y @ y l nC ;
@y * * r @y ;
Y ] ] l Ya ;
Y * * l Y ;
Ya _ Y r @Y ;
Ya * * l Ya ;
@Y @ Y l nC ;
@Y * * r @Y ;
z ] ] l za ;
z * * l z ;
za _ z r @z ;
za * * l za ;
@z @ z l nC ;
@z * * r @z ;
Z ] ] l Za ;
Z * * l Z ;
Za _ Z r @Z ;
Za * * l Za ;
@Z @ Z l nC ;
@Z * * r @Z ;
Sp ] ] l Sp1 ;
Sp * * l Sp ;
Sp1 _ ~ r @Sp ;
Sp1 * * l Sp1 ;
@Sp @ _ l nC ;
@Sp * * r @Sp ;
nC _ @ l Sp ;
nC 0 0 * 9 ;
nC 1 1 * 9 ;
nC 2 2 * 9 ;
nC 3 3 * 9 ;
nC 4 4 * 9 ;
nC 5 5 * 9 ;
nC 6 6 * 9 ;
nC 7 7 * 9 ;
nC 8 8 * 9 ;
nC 9 9 * 9 ;
nC - - * 9 ;
nC a a * 9 ;
nC A A * 9 ;
nC b b * 9 ;
nC B B * 9 ;
nC c c * 9 ;
nC C C * 9 ;
nC d d * 9 ;
nC D D * 9 ;
nC e e * 9 ;
nC E E * 9 ;
nC f f * 9 ;
nC F F * 9 ;
nC g g * 9 ;
nC G G * 9 ;
nC h h * 9 ;
nC H H * 9 ;
nC i i * 9 ;
nC I I * 9 ;
nC j j * 9 ;
nC J J * 9 ;
nC k k * 9 ;
nC K K * 9 ;
nC l l * 9 ;
nC L L * 9 ;
nC m m * 9 ;
nC M M * 9 ;
nC n n * 9 ;
nC N N * 9 ;
nC o o * 9 ;
nC O O * 9 ;
nC p p * 9 ;
nC P P * 9 ;
nC q q * 9 ;
nC Q Q * 9 ;
nC r r * 9 ;
nC R R * 9 ;
nC s s * 9 ;
nC S S * 9 ;
nC t t * 9 ;
nC T T * 9 ;
nC u u * 9 ;
nC U U * 9 ;
nC v v * 9 ;
nC V V * 9 ;
nC w w * 9 ;
nC W W * 9 ;
nC x x * 9 ;
nC X X * 9 ;
nC y y * 9 ;
nC Y Y * 9 ;
nC z z * 9 ;
nC Z Z * 9 ;
nC ( ( * fC ;
fC ] ] l fC1 ;
fC * * l fC ;
fC1 _ [ * cl ;
fC1 * * l fC1 ;
cl [ _ r cl ;
cl ] _ r cl ;
cl ~ _ r cl ;
cl ( _ r clO ;
clO ) _ * halt-accept ;
clO * _ r clO ;
cl ) ) * halt-accept ;
cl * * r cl ;
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; Olc r _ * Olc
; tpecca-tlah * _ ) Olc
; Olc r _ ( lc
; lc r _ ~ lc
; lc r _ ] lc
; lc r _ [ lc
; 1Cf l * * 1Cf
; lc * [ _ 1Cf
; Cf l * * Cf
; 1Cf l ] ] Cf
; Cf * ) ) Cn
; 9 * Z Z Cn
; 9 * z z Cn
; 9 * Y Y Cn
; 9 * y y Cn
; 9 * X X Cn
; 9 * x x Cn
; 9 * W W Cn
; 9 * w w Cn
; 9 * V V Cn
; 9 * v v Cn
; 9 * U U Cn
; 9 * u u Cn
; 9 * T T Cn
; 9 * t t Cn
; 9 * S S Cn
; 9 * s s Cn
; 9 * R R Cn
; 9 * r r Cn
; 9 * Q Q Cn
; 9 * q q Cn
; 9 * P P Cn
; 9 * p p Cn
; 9 * O O Cn
; 9 * o o Cn
; 9 * N N Cn
; 9 * n n Cn
; 9 * M M Cn
; 9 * m m Cn
; 9 * L L Cn
; 9 * l l Cn
; 9 * K K Cn
; 9 * k k Cn
; 9 * J J Cn
; 9 * j j Cn
; 9 * I I Cn
; 9 * i i Cn
; 9 * H H Cn
; 9 * h h Cn
; 9 * G G Cn
; 9 * g g Cn
; 9 * F F Cn
; 9 * f f Cn
; 9 * E E Cn
; 9 * e e Cn
; 9 * D D Cn
; 9 * d d Cn
; 9 * C C Cn
; 9 * c c Cn
; 9 * B B Cn
; 9 * b b Cn
; 9 * A A Cn
; 9 * a a Cn
; 9 * - - Cn
; 9 * 9 9 Cn
; 9 * 8 8 Cn
; 9 * 7 7 Cn
; 9 * 6 6 Cn
; 9 * 5 5 Cn
; 9 * 4 4 Cn
; 9 * 3 3 Cn
; 9 * 2 2 Cn
; 9 * 1 1 Cn
; 9 * 0 0 Cn
; pS l @ _ Cn
; pS@ r * * pS@
; Cn r _ @ pS@
; 1pS l * * 1pS
; pS@ r ~ _ 1pS
; pS l * * pS
; 1pS l ] ] pS
; Z@ r * * Z@
; Cn r Z @ Z@
; aZ l * * aZ
; Z@ r Z _ aZ
; Z l * * Z
; aZ l ] ] Z
; z@ r * * z@
; Cn r z @ z@
; az l * * az
; z@ r z _ az
; z l * * z
; az l ] ] z
; Y@ r * * Y@
; Cn r Y @ Y@
; aY l * * aY
; Y@ r Y _ aY
; Y l * * Y
; aY l ] ] Y
; y@ r * * y@
; Cn r y @ y@
; ay l * * ay
; y@ r y _ ay
; y l * * y
; ay l ] ] y
; X@ r * * X@
; Cn r X @ X@
; aX l * * aX
; X@ r X _ aX
; X l * * X
; aX l ] ] X
; x@ r * * x@
; Cn r x @ x@
; ax l * * ax
; x@ r x _ ax
; x l * * x
; ax l ] ] x
; W@ r * * W@
; Cn r W @ W@
; aW l * * aW
; W@ r W _ aW
; W l * * W
; aW l ] ] W
; w@ r * * w@
; Cn r w @ w@
; aw l * * aw
; w@ r w _ aw
; w l * * w
; aw l ] ] w
; V@ r * * V@
; Cn r V @ V@
; aV l * * aV
; V@ r V _ aV
; V l * * V
; aV l ] ] V
; v@ r * * v@
; Cn r v @ v@
; av l * * av
; v@ r v _ av
; v l * * v
; av l ] ] v
; U@ r * * U@
; Cn r U @ U@
; aU l * * aU
; U@ r U _ aU
; U l * * U
; aU l ] ] U
; u@ r * * u@
; Cn r u @ u@
; au l * * au
; u@ r u _ au
; u l * * u
; au l ] ] u
; T@ r * * T@
; Cn r T @ T@
; aT l * * aT
; T@ r T _ aT
; T l * * T
; aT l ] ] T
; t@ r * * t@
; Cn r t @ t@
; at l * * at
; t@ r t _ at
; t l * * t
; at l ] ] t
; S@ r * * S@
; Cn r S @ S@
; aS l * * aS
; S@ r S _ aS
; S l * * S
; aS l ] ] S
; s@ r * * s@
; Cn r s @ s@
; as l * * as
; s@ r s _ as
; s l * * s
; as l ] ] s
; R@ r * * R@
; Cn r R @ R@
; aR l * * aR
; R@ r R _ aR
; R l * * R
; aR l ] ] R
; r@ r * * r@
; Cn r r @ r@
; ar l * * ar
; r@ r r _ ar
; r l * * r
; ar l ] ] r
; Q@ r * * Q@
; Cn r Q @ Q@
; aQ l * * aQ
; Q@ r Q _ aQ
; Q l * * Q
; aQ l ] ] Q
; q@ r * * q@
; Cn r q @ q@
; aq l * * aq
; q@ r q _ aq
; q l * * q
; aq l ] ] q
; P@ r * * P@
; Cn r P @ P@
; aP l * * aP
; P@ r P _ aP
; P l * * P
; aP l ] ] P
; p@ r * * p@
; Cn r p @ p@
; ap l * * ap
; p@ r p _ ap
; p l * * p
; ap l ] ] p
; O@ r * * O@
; Cn r O @ O@
; aO l * * aO
; O@ r O _ aO
; O l * * O
; aO l ] ] O
; o@ r * * o@
; Cn r o @ o@
; ao l * * ao
; o@ r o _ ao
; o l * * o
; ao l ] ] o
; N@ r * * N@
; Cn r N @ N@
; aN l * * aN
; N@ r N _ aN
; N l * * N
; aN l ] ] N
; n@ r * * n@
; Cn r n @ n@
; an l * * an
; n@ r n _ an
; n l * * n
; an l ] ] n
; M@ r * * M@
; Cn r M @ M@
; aM l * * aM
; M@ r M _ aM
; M l * * M
; aM l ] ] M
; m@ r * * m@
; Cn r m @ m@
; am l * * am
; m@ r m _ am
; m l * * m
; am l ] ] m
; L@ r * * L@
; Cn r L @ L@
; aL l * * aL
; L@ r L _ aL
; L l * * L
; aL l ] ] L
; l@ r * * l@
; Cn r l @ l@
; al l * * al
; l@ r l _ al
; l l * * l
; al l ] ] l
; K@ r * * K@
; Cn r K @ K@
; aK l * * aK
; K@ r K _ aK
; K l * * K
; aK l ] ] K
; k@ r * * k@
; Cn r k @ k@
; ak l * * ak
; k@ r k _ ak
; k l * * k
; ak l ] ] k
; J@ r * * J@
; Cn r J @ J@
; aJ l * * aJ
; J@ r J _ aJ
; J l * * J
; aJ l ] ] J
; j@ r * * j@
; Cn r j @ j@
; aj l * * aj
; j@ r j _ aj
; j l * * j
; aj l ] ] j
; I@ r * * I@
; Cn r I @ I@
; aI l * * aI
; I@ r I _ aI
; I l * * I
; aI l ] ] I
; i@ r * * i@
; Cn r i @ i@
; ai l * * ai
; i@ r i _ ai
; i l * * i
; ai l ] ] i
; H@ r * * H@
; Cn r H @ H@
; aH l * * aH
; H@ r H _ aH
; H l * * H
; aH l ] ] H
; h@ r * * h@
; Cn r h @ h@
; ah l * * ah
; h@ r h _ ah
; h l * * h
; ah l ] ] h
; G@ r * * G@
; Cn r G @ G@
; aG l * * aG
; G@ r G _ aG
; G l * * G
; aG l ] ] G
; g@ r * * g@
; Cn r g @ g@
; ag l * * ag
; g@ r g _ ag
; g l * * g
; ag l ] ] g
; F@ r * * F@
; Cn r F @ F@
; aF l * * aF
; F@ r F _ aF
; F l * * F
; aF l ] ] F
; f@ r * * f@
; Cn r f @ f@
; af l * * af
; f@ r f _ af
; f l * * f
; af l ] ] f
; E@ r * * E@
; Cn r E @ E@
; aE l * * aE
; E@ r E _ aE
; E l * * E
; aE l ] ] E
; e@ r * * e@
; Cn r e @ e@
; ae l * * ae
; e@ r e _ ae
; e l * * e
; ae l ] ] e
; D@ r * * D@
; Cn r D @ D@
; aD l * * aD
; D@ r D _ aD
; D l * * D
; aD l ] ] D
; d@ r * * d@
; Cn r d @ d@
; ad l * * ad
; d@ r d _ ad
; d l * * d
; ad l ] ] d
; C@ r * * C@
; Cn r C @ C@
; aC l * * aC
; C@ r C _ aC
; C l * * C
; aC l ] ] C
; c@ r * * c@
; Cn r c @ c@
; ac l * * ac
; c@ r c _ ac
; c l * * c
; ac l ] ] c
; B@ r * * B@
; Cn r B @ B@
; aB l * * aB
; B@ r B _ aB
; B l * * B
; aB l ] ] B
; b@ r * * b@
; Cn r b @ b@
; ab l * * ab
; b@ r b _ ab
; b l * * b
; ab l ] ] b
; A@ r * * A@
; Cn r A @ A@
; aA l * * aA
; A@ r A _ aA
; A l * * A
; aA l ] ] A
; a@ r * * a@
; Cn r a @ a@
; aa l * * aa
; a@ r a _ aa
; a l * * a
; aa l ] ] a
; 9@ r * * 9@
; Cn r 9 @ 9@
; a9c l * * a9c
; 9@ r 9 _ a9c
; 9c l * * 9c
; a9c l ] ] 9c
; 8@ r * * 8@
; Cn r 8 @ 8@
; a8c l * * a8c
; 8@ r 8 _ a8c
; 8c l * * 8c
; a8c l ] ] 8c
; 7@ r * * 7@
; Cn r 7 @ 7@
; a7c l * * a7c
; 7@ r 7 _ a7c
; 7c l * * 7c
; a7c l ] ] 7c
; 6@ r * * 6@
; Cn r 6 @ 6@
; a6c l * * a6c
; 6@ r 6 _ a6c
; 6c l * * 6c
; a6c l ] ] 6c
; 5@ r * * 5@
; Cn r 5 @ 5@
; a5c l * * a5c
; 5@ r 5 _ a5c
; 5c l * * 5c
; a5c l ] ] 5c
; 4@ r * * 4@
; Cn r 4 @ 4@
; a4c l * * a4c
; 4@ r 4 _ a4c
; 4c l * * 4c
; a4c l ] ] 4c
; 3@ r * * 3@
; Cn r 3 @ 3@
; a3c l * * a3c
; 3@ r 3 _ a3c
; 3c l * * 3c
; a3c l ] ] 3c
; 2@ r * * 2@
; Cn r 2 @ 2@
; a2c l * * a2c
; 2@ r 2 _ a2c
; 2c l * * 2c
; a2c l ] ] 2c
; 1@ r * * 1@
; Cn r 1 @ 1@
; a1c l * * a1c
; 1@ r 1 _ a1c
; 1c l * * 1c
; a1c l ] ] 1c
; 0@ r * * 0@
; Cn r 0 @ 0@
; a0c l * * a0c
; 0@ r 0 _ a0c
; 0c l * * 0c
; a0c l ] ] 0c
; Z l @ Z 9
; z l @ z 9
; Y l @ Y 9
; y l @ y 9
; X l @ X 9
; x l @ x 9
; W l @ W 9
; w l @ w 9
; V l @ V 9
; v l @ v 9
; U l @ U 9
; u l @ u 9
; T l @ T 9
; t l @ t 9
; S l @ S 9
; s l @ s 9
; R l @ R 9
; r l @ r 9
; Q l @ Q 9
; q l @ q 9
; P l @ P 9
; p l @ p 9
; O l @ O 9
; o l @ o 9
; N l @ N 9
; n l @ n 9
; M l @ M 9
; m l @ m 9
; L l @ L 9
; l l @ l 9
; K l @ K 9
; k l @ k 9
; J l @ J 9
; j l @ j 9
; I l @ I 9
; i l @ i 9
; H l @ H 9
; h l @ h 9
; G l @ G 9
; g l @ g 9
; F l @ F 9
; f l @ f 9
; E l @ E 9
; e l @ e 9
; D l @ D 9
; d l @ d 9
; C l @ C 9
; c l @ c 9
; B l @ B 9
; b l @ b 9
; A l @ A 9
; a l @ a 9
; 9c l @ 9 9
; 8c l @ 8 9
; 7c l @ 7 9
; 6c l @ 6 9
; 5c l @ 5 9
; 4c l @ 4 9
; 3c l @ 3 9
; 2c l @ 2 9
; 1c l @ 1 9
; 0c l @ 0 9
; 8 r * * 8
; 9 r ( ( 8
; 8 r ] _ 7
; 7 l _ _ 6
; 5 l * * 5
; 0 * ( ( 5
; 3 r * * 3
; 5 l ) _ )3
; 3 r * * 4
; )3 l _ _ 4
; 4 r _ _ 3
; 3 r ( _ 2
; 2 l _ _ 1
; 2 l * * 0
; 6 l ( ( 0

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Try it reversed!

I used this site to reverse it.

Answer 12

Pyth, 5 3 bytes

z_k

-2 bytes by realizing the newline flips around anyways

Explanation:

z   # Implicitly print the input
 _k # Implicitly print the reversed empty string

Reversed Explanation:

k     # Implicitly print the empty string
 _z   # Implicitly print the reversed input

Answer 13

Gaia, 2 bytes

pv

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Try it reversed!

Very similar solution to other golfing languages.

Explanation

p    Print the (implicitly grabbed) input
 v   Reverse the input

Reverse

v    Reverse the (implicitly grabbed) input
 p   Print the result

Answer 14

Jelly, 2 bytes

Uṛ

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Reversed!

Explanation

U  | Reverse
 ṛ | Right argument (when used in a monadic chain like this, will return the original argument to the chain)

Explanation (reversed)

ṛ  | Right argument (when used in a monadic chain and followed by a monadic link, will return the output of that monadic link)
 U | Reverse

Seven other two-byters Ṛṛ ḷU ḷṚ Uȧ Ṛȧ ȯU ȯṚ

Answer 15

Japt, 2 bytes

ÔU

Try it | Reversed

Answer 16

Cubix, 19 bytes

.@o?A^;/|?$oqBA.UW.

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Cubified

    . @
    o ?
A ^ ; / | ? $ o
q B A . U W . .
    . .
    . .

• A^ get all the input and enter the loop
• o? output the TOS of stack and test
• @ exit if it tests to negative
• /;^ reflect back, pop TOS and re-enter loop

All other commands are avoided.

Reversed

.WU.ABqo$?|/;^A?o@.

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Cubified

   . W
    U .
A B q o $ ? | /
; ^ A ? o @ . .
    . .
    . .

• ABq Get all input, reverse and drop TOS to bottom of stack
• o$?|? output TOS, skip the test and relect back onto test
• @ halt if test if negative
• WUq change lane, u-turn onto drop TOS start of loop

Answer 17

Wolfram Language (Mathematica), 16 bytes

1&esreveR//#& &1

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Reversed:

1& &#//Reverse&1

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Takes a list of characters as input. For string input, use StringReverse.

Answer 18

Pip, 4 bytes

aVRa

Try it online! !enilno ti yrT

Makes use of the fact that RV is the reverse operator but VR is an undefined variable. Both versions print the value of their last expression; in the standard version, that's a (with the first a and the VR being no-ops), while in the reversed version, that's RVa (with the first a being a no-op).

Answer 19

Perl 5 -p, 11 bytes

The obvious.

#esrever=_$

Answer 20

Kotlin, 15 bytes

My first Kotlin answer, and far shorter than the java equivalent!

s//)(desrever.s

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Reversed:

s.reversed()//s

!enilno ti yrT

Answer 21

MathGolf, 3 bytes

x;l

Explanation:

x   Reverse the implicit input
 ;  Discard the string
  l Push a string input
Implicit output TOS

Reversed:

l   Push a string input
 ;  Discard it
  x Reverse the implicit input
Implicit output TOS

Answer 22

Pushy, 4 bytes

"\"@

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Simple implementation with the comment character \. In the forwards program, " prints the input and the rest is a comment; in the backwards program, @ reverses the input before printing.

We could alternatively replace \ with c, which would clear the input from the stack.

Answer 23

J, 7 bytes

,&.|:@]

Reversed:

]@:|.&,

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Jonah's comment on Adam's APL answer made me take the challenge. It was pretty hard indeed, because the inflections . and : always attach to the symbol on their left, and a sole | (abstract value) isn't happy with strings.

How these work

Basically, it is a random mix of no-ops connected through various connectors.

,&.|:@]
     @]   Pass the argument unchanged
 &.|:     Apply inverse of |: (transpose), no-op on single string
,         Ravel, no-op on a single string
 &.|:     Apply |: again, still no-op

]@:|.&,
     &,   Ravel, no-op
 @:|.     Reverse
]         Pass the argument unchanged

This answer is one byte shorter than the trivial comment-abuse:

J, 8 bytes

]NB.BN.|

Reversed:

|.NB.BN]

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In J, the in-line comment marker is NB., which is longer than every other language I know of.

Answer 24

W, 2 bytes

Pretty much the same as the 05AB1E solution.

a_

Explanation

a   % Push the input
 _  % Reverse the input
    % Implicit print the top of the stack

noitanalpxE

_   % Reverse the implicit input
 a  % Push the input
    % Implicit print the top of the stack

Answer 25

Brain-Flak, 13 bytes

#><}><)><}{({

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Forward: Just a comment, so that it just outputs the input

Reversed:

{({}<>)<>}<>#

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Move everything to the second stack, so it is reversed.

Answer 26

CJam, 7 bytes

qe#e%Wq

Boring version with comments. If CJam would fail silently i could have saved like 3 bytes in 2 questions already!

• Try it online!
• Try it reversed!

Answer 27

Stax, 2 bytes

Pr

Run it Reversed

Answer 28

PHP, 27 bytes

<?=$argn;#;)ngra$(verrts=?<

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Answer 29

C (gcc), 56 bytes

Nothing fancy. Would have used puts() but then trailing whitespace would not have been consistent between the two variants.

f(int*s){printf(s);}//};))1+s(f,s*(rahctup&&s*{)s*rahc(f

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f(char*s){*s&&putchar(*s,f(s+1));}//};)s(ftnirp{)s*tni(f

Reversed!