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C@ (cat) is an esolang speedran by User:BoundedBeans. Let’s see how long it takes to write this exclusive specification.

All characters of input are pushed onto the stack at the start of the program.

Commands[edit]

: duplicate
/ swap
$ discard
. print
Anything else: push to the stack.

Examples[edit]

5-character text reverser[edit]

.....

One character cat/Quine[edit]

.

This is normally a one character cat taking the last character, but if the input is ., this program is a quine. In fact, any program consisting of only dots is a quine if given only dots as the last (program length) characters of input.

Two character cat[edit]

/..

Bigger cats[edit]

C@ cannot create any larger cats than two characters, though it can make text reversers, and it can make quines of any size.

Text scrambler[edit]

Will scramble the last 10 characters of text

/../../../../../../../../../..

Insert "CAT" into reversed text after every character[edit]

Works with 10 characters.

C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..C.A.T..

Hello world[edit]

H.e.l.l.o. .w.o.r.l.d.!.

Alternatively:

!dlrow olleH............

Use[edit]

This may be a somewhat useful language for text-processing algorithms that:

• do not have any sort of randomness or conditionals
• do not have loops other than defined for loops
• process text in reverse and not in any other order
• process the last characters of input rather than the first
• process a defined number of characters
• have exactly one possible output for each possible input
• do not insert colons, forward slashes, dollar signs or periods anywhere
• only ever work with two characters at a time

Implementation[edit]

Implementation in Python (which I'm just learning, so forgive me if it's bad):

program = "....." #<- insert program here

stack = input("")
output = ""
 
for i in program:
    if i == ":":
        stack += stack[-1]
    elif i == "/":
        stack = stack[:-2] + stack[-1] + stack[-2]
    elif i == "$":
        stack = stack[:-1]
    elif i == ".":
        output += stack[-1]
        stack = stack[:-1]
    else:
        stack += i
 
print(output) 

#input command is here so that you can see the output when directly running the file through File Explorer
#as soon as you press enter the program will end
input("")