# I reverse the source code, you reverse the input!

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.

# JavaScript, 32 bytes

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


Reversed:

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

• Well done, didn't know JS doesn't have a builtin reverse for strings. By the way, TIO links usually make answers more likable: Try it online! Reversed – Night2 Sep 22 '19 at 14:12
• There is no string reverse. [...s] converts to array, which is reversed then joined back together as a string. – James Sep 22 '19 at 14:59
• If you also stumbled over .join - have a look at Tagged Templates – nitzel Sep 23 '19 at 9:37

# Bash, 9 bytes

cat # ver


Reversed:

rev # tac

• This would be easier if the challenge was to reverse the line order; then I could just use cat. – S.S. Anne Sep 23 '19 at 11:43

# APL (Dyalog Unicode), 3 2 bytesSBCS

-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: [3,2,1][[3,2,1]]

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

• Nice. Digraphs make this more difficult in J... haven’t come up with anything yet – Jonah Sep 22 '19 at 15:31

# Keg, 3 2 bytes

#?


## 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

^#?


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

• interpreter where – ASCII-only Feb 27 at 11:26

# Ruby, 21 bytes

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


Try it online!

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


!enilno ti yrT

id--esrever


## 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.

# 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


# Turing Machine Language, 1432414321 13257 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;
Ia * * l Ia;
@I @ I l nC;
@I * * r @I;
j ] ] l ja;
j * * l j;
ja _ j r @j;
ja * * l ja;
@j @ j l nC;
@j * * r @j;
J ] ] l Ja;
J * * l J;
Ja _ J r @J;
Ja * * l Ja;
@J @ J l nC;
@J * * r @J;
k ] ] l ka;
k * * l k;
ka _ k r @k;
ka * * l ka;
@k @ k l nC;
@k * * r @k;
K ] ] l Ka;
K * * l K;
Ka _ K r @K;
Ka * * l Ka;
@K @ K l nC;
@K * * r @K;
l ] ] l la;
l * * l l;
la _ l r @l;
la * * l la;
@l @ l l nC;
@l * * r @l;
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;
@m @ m l nC;
@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;
@o @ o l nC;
@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;
@S @ S l nC;
@S * * r @S;
t ] ] l ta;
t * * l t;
ta _ t r @t;
ta * * l ta;
@t @ t l nC;
@t * * r @t;
T ] ] l Ta;
T * * l T;
Ta _ T r @T;
Ta * * l Ta;
@T @ T l nC;
@T * * r @T;
u ] ] l ua;
u * * l u;
ua _ u r @u;
ua * * l ua;
@u @ u l nC;
@u * * r @u;
U ] ] l Ua;
U * * l U;
Ua _ U r @U;
Ua * * l Ua;
@U @ U l nC;
@U * * r @U;
v ] ] l va;
v * * l v;
va _ v r @v;
va * * l va;
@v @ v l nC;
@v * * r @v;
V ] ] l Va;
V * * l V;
Va _ V r @V;
Va * * l Va;
@V @ V l nC;
@V * * r @V;
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;
;lc r * * lc
;tpecca-tlah * ) ) lc
;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@
;D l * * D
;d@ r * * d@
;Cn r d @ d@
;d 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


Try it online!

Try it reversed!

I used this site to reverse it.

• Well...! I hope you haven't written the first half, manually! I really hope! – Night2 Sep 26 '19 at 14:23
• It really wasn't that much once I had the strategy sorted. After the basic logic was laid out, it was mostly copy/pasting/tweaking followed by debugging my muffed attempts at copy/pasting/tweaking. – ouflak Sep 26 '19 at 15:33

# Python 3, 27 bytes

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


Try it online!

!enilno ti yrT

# 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.

# Gaia, 2 bytes

pv


Try it online!

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

• Well that's certainly efficient. – ouflak Oct 24 '19 at 18:47

# 05AB1E, 2 bytes

RI


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)


# Pip, 4 bytes

aVRa


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).

# Pushy, 4 bytes

"\"@


Try it online: Forwards, Backwards

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.

# J, 7 bytes

,&.|:@]


Reversed:

]@:|.&,


Try it online!

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]


Try it online!

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

# Jelly, 2 bytes

Uṛ


Try it online!

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

# Japt, 2 bytes

ÔU


# Cubix, 19 bytes

.@o?A^;/|?$oqBA.UW.  Try it online! Cubified  . @ o ? A ^ ; / | ?$ 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$?|/;^A?o@.  Try it online! Cubified  . W U . A B q o$ ? | /
; ^ A ? o @ . .
. .
. .

• ABq Get all input, reverse and drop TOS to bottom of stack
• o$?|? output TOS, skip the test and relect back onto test • @ halt if test if negative • WUq change lane, u-turn onto drop TOS start of loop # Wolfram Language (Mathematica), 16 bytes 1&esreveR//#& &1  Try it online! Reversed: 1& &#//Reverse&1  Try it online! Takes a list of characters as input. For string input, use StringReverse. # Perl 5-p, 11 bytes The obvious. #esrever=_$


## MathGolf, 3 bytes

x;l


## Explanation:

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


Reversed:

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


# Kotlin, 15 bytes

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

s//)(desrever.s


Try it online!

Reversed:

s.reversed()//s


!enilno ti yrT

• The parenthesis are the wrong way. A more correct answer would be s//)(desrever.s. However i think it is custom to provide at least a full lambda in Kotlin (or at least Java). So something like {it}//})(desrever.ti{ should do the trick. – Roman Gräf Sep 25 '19 at 15:36

# 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


Try it online!

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


Reversed!

## 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


# Brain-Flak, 13 bytes

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


Try it online!

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

Reversed:

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


Try it online!

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

# 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!

# Stax, 2 bytes

Pr


# PHP, 27 bytes

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


Try it online!

‮Try it online!

# x86 opcode, 19 bytes

85 c9 7e 0e 49 8a 06 8a 24 0e 88 26 88 04 0e 46 e2 ee c3


!enilno ti yrT

# 17 bytes

f:  cmp esi, edi
jae ok
dec edi
mov al, [esi]
mov ah, [edi]
mov [esi], ah
mov [edi], al
inc esi
jmp f
ok: ret


input esi(begin) and edi(end)