YABC
YABC, acronum for Yet Another Brainfuck Clone, is a brainfuck-derivative scribbled up by oklopol for testing how uploading to the esolang wiki works.
Language overview
YABC has a brainfuck-like tape, that extends infinitely to the right. Tape cells hold signed bignums. Current cell is the leftmost cell when the program starts. Code is read one character at a time, executing the character read as an instruction. Instructions:
| Command | Description |
|---|---|
>
|
Move the pointer to the right |
<
|
Move the pointer to the left |
+
|
Increment the memory cell under the pointer |
-
|
Decrement the memory cell under the pointer |
^
|
If the cell to the right of current cell is nonzero, take the value of the current cell and jump that many characters backwards in code |
Computational class
YABC is Turing complete.
YABC from Brainfuck
The following implements a Brainfuck dialect with nonnegative integer number cells, without I/O.
We assume that ^ allows negative offsets, which are relative to the ^ instruction itself.
Cell values will be kept between -37 and the larger value of 41 or the 1 plus the maximum value of the Brainfuck dialect.
Translation
First, there is a preamble.
- repeat
+++++++++++++++++++++++++++++++++++++++++>------------------------------------->for each nesting level of loops of the Brainfuck code +++++++++++++++++++++++++++++++>-->------>++>++>+>+++>+>------>+++>+>------>-<^>>>^<
This is followed by the translated Brainfuck code.
Each Brainfuck operation is translated to 39 YABC instructions, according to the following table, where ? stands for an arbitrary instruction that will never be executed.
Command Code +><><><><><><><><><<+>^??><^^??><^^>>>^<-><><><><><><><><><<->^??><^^??><^^>>>^<>><><>++++>+>------>-<^??><^^??><^^>>>^<<><><>+<++++++<-<----<^??><^^??><^^>>>^<[<-<<>^>+<<^>>+>^><<<^^>^>>^^?<<<^^>>>^<]><><><><<<<<<^?>^????^<<<<^^??>>^^>>>^<
Notes
The tape layout is as follows,
41 -37 ... 41 -37 31 -2 -6 2 2 1 3 1 -6 3 ?+1 -6 ... 3 ?+1 *-6 -1 ? 0 0 ? 0 0 ...
where the first line gives fixed constants, and the second line the data area.
The question marks stand for tape values from the original Brainfuck program, and * indicates the current pointer at the start of each translated instruction.
The encoding of the instructions have the following format:
code******************^left*^right^enter
Normal execution uses the code part; the -6 values on the tape are used as offsets to skip over the other parts using the fixed ^ operations.
The left part is used for skipping over loops, moving to the left.
It uses the beginning of the tape as a control area; in each left block, two instructions (<<, ><, >>) are executed, followed by a ^.
Normally, the pointer will point at a 41, which is the offset for skipping to previous instruction's left block.
The pointer can move to the left and right, keeping track of the nesting depth. The ] operation moves the pointer to the last 41 at the beginning of the tape.
When the matching [ is found, the offset is 31, jumping to the enter part of the preceding instruction.
Similarly, the right part is used for skipping over loops, moving rightwards.
The [ instruction is responsible for conditionally entering its right part while pointing to the last -37 at the beginning of the tape.
-37 is the offset required to jump to the next instruction's right part.
When the matching ] instruction is found, the offset will be -2 and execution continues at the enter part of the ] instruction.
Finally, the enter part, which is always >>>^<, is responsible for resetting the tape position to the current cell.
It uses the magic 3 and -1 values in the data area of the tape, and the 2 1 3 part of the preamble for synchronization (the code works when the pointer points to either of the 31 or the -2 offsets in the preamble).
Note that the preamble contains a copy of the enter code.