?index.php

?index.php is an esoteric programming language by User:Dragoneater67.

Overview

Commands are executed 1-by-1 left-to-right. The language operates on a stack of strings. Popping from an empty stack results in an error.

Commands

Command	Description
"s"	Push s to the stack.
'	Pop a string from the stack and execute it as a program in a separate thread.
1	Pop a string from the stack and print it as h1.
2	Pop a string from the stack and print it as h2.
3	Pop a string from the stack and print it as h3.
4	Pop a string from the stack and print it as h4.
5	Pop a string from the stack and print it as h5.
6	Pop a string from the stack and print it as h6.
#	Pop a string from the stack and print it as a regular string.
*	Pop a string from the stack and print it as a bold string.
/	Pop a string from the stack and print it as an italic string.
-	Pop a string from the stack and print it as a bullet point.
_	Pop a string from the stack and print it as an underlined string.
%	Duplicate top of the stack.
+	Pop 2 strings from the stack, concatenate them and push the result back.
=	Pop 2 strings from the stack, push "TRUE" if they're equal, else, push "".
>	Pop 2 strings from the stack, push "TRUE" if the second element is longer than the first, else, push "".
<	Pop 2 strings from the stack, push "TRUE" if the second element is shorter than the first, else, push "".
~	Pop a string from the stack, push "TRUE" if it is non-empty, else push "".
&	Pop 2 strings from the stack, push "TRUE" if both are non-empty, else, push "".
	Pop 2 strings from the stack, push "TRUE" if at least 1 string is non-empty, else, push "".
?	Push a random character to the stack.
!	Pop a string from the stack, if it's a custom command, execute it as a subprogram, else, execute it as a shell command and pop the entire stack which will be the arguments.
$	Pop 2 strings from the stack, (re)define a variable where the first string is the name, and the second string is the value.
@	Pop a string from the stack, push the value of the variable with the same name as the popped string.
`	Discard top of the stack.
^	Pop a string from the stack, append it to the current (sub)program.
\	Push the current (sub)program to the stack.
:	Pop 2 string from the stack, (re)define a custom command where the first string is the name, and the second string is the subprogram.
;	Swap 2 top elements of the stack.
,	Push a newline to the stack.
.	Halt.

Examples

Hello, world!

"Hello, world!",+#

XKCD Random Number

"4",+#

Truth machine

"#""0":"%#\^""1":"i"%!

Where i is the input.

Infinite loop

\^

The kids choice awards

"slime"#\^

Quine

\#

External resources

• Codeberg repository