Pepp*erdine
Pepp*erdine is an esoteric programming language by Brody Maddox, based off of Chicken by Torbjörn Söderstedt, in which "pep", "erdine" and concatenations of 'p' are the only valid symbols.
Language overview
A chicken program consists of the tokens "pep", "erdine", varying length strings of 'p', and "\n". The first line begins with 'pep', and the final line has 'erdine'. Every line in between has a number of 'p's joined together. The number of 'p's corresponds to an opcode. Trailing newlines are significant, as an empty line will produce a "0" opcode.
Instructions are loaded onto the stack and executed there directly, which allows for injecting arbitrary code and executing it through a jump. Self-modifying code is also possible because the program stack is not bounded.
The user is able to supply an input value before executing the program. This input is stored in one of the two registers.
Memory model
The stack (represents the memory of the program) has three segments.
The first segment contains two registers. The first register just points to the stack itself (by reference). The second register contains the user input, which is usually a string. These registers are used by the LOAD instruction.
The second segment contains the loaded code. For each line of the code there is a cell on the stack containing the amount of 'p's on that line. This segment is directly used for execution. It is automatically padded with a single EXIT instruction.
The third segment contains the actual program stack. As instructions are executed, they will push and pop values in this space. Since the segments are not isolated, it is possible to modify values in the code space or execute in the user stack space.
Instructions
Pepp*erdine supports the following instructions:
| Opcode | Name | Description |
|---|---|---|
0
|
exit | Stop execution. |
1
|
p | Push the string "p" onto the stack. |
2
|
add | Add two top stack values. |
3
|
subtract | Subtract two top stack values. |
4
|
multiply | Multiply two top stack values. |
5
|
compare | Compare two top stack values for equality, push truthy or falsy result onto the stack. |
6
|
load | Double wide instruction. Next instruction indicates source to load from. 0 loads from stack, 1 loads from user input. Top of stack points to address/index to load onto stack. |
7
|
store | Top of stack points to address/index to store to. The value below that will be popped and stored. |
8
|
jump | Top of stack is a relative offset to jump to. The value below that is the condition. Jump only happens if condition is truthy. |
9
|
char | Interprets the top of the stack as ascii and pushes the corresponding character. |
10+
|
push | Pushes the literal number n-10 onto the stack. |
Examples
Hello, world!
pep pppppppppppppppppppp pppppppppppppppppppp pppp ppppppppp ppppppppppp ppppppp pppppppppp pppppppppppppppp pppppppppppppppp pppp ppp pppppppppp ppppppppppppppppp ppp pppppppppp pppppppppp ppppppppppppp ppppppppppp pppppppppppp pppppp ppp pppppppppppppp pppp ppppppppppppppppppppp ppppppppppppp pppppppppppppppp pppppppppp ppppppppppppppp ppppppppppppp pppppp pppp pppppppppppppppppp pp pp ppppppppp ppppppppppp pppppp pp ppppppppppp ppppppp pppppppppppp pppppp pppppppppppp ppp pppppppppppp ppppppp pppppppppppp pppppp pppppppppp ppppppppppppppppppppppppppppppppppppppp ppp pppppppp ppppppppppp pppppp erdine
External resources
- [1] Python implementation