ABCLang

ABCLang is a minimalistic, Turing-complete esoteric programming language created by User:Jan Ala. It uses only three characters: a, b, and c.

Overview

ABCLang is a stack-based virtual machine language with:

• 3 characters (a, b, c)
• 26 instructions (encoded as 3-character sequences)
• Two stacks (A and B) for data
• One register for temporary storage
• Turing-complete via dual-stack simulation of a Turing machine

Encoding System

Base-26 Digit Encoding

Each base-26 digit (0-25) is encoded as a 3-character abc sequence:

Value	Code	Value	Code	Value	Code
0	aaa	9	baa	18	caa
1	aab	10	bab	19	cab
2	aac	11	bac	20	cac
3	aba	12	bba	21	cba
4	abb	13	bbb	22	cbb
5	abc	14	bbc	23	cbc
6	aca	15	bca	24	cca
7	acb	16	bcb	25	ccb
8	acc	17	bcc

Note: ccc is the terminator marker, not a valid instruction or digit.

Numbers

Numbers are encoded in base-26, little-endian format:

42 = 1×26 + 16
= [16, 1]
= bcb aab + ccc (terminator marker)
= bcbaabccc

Examples:

Number	Base-26	Little-Endian	ABC Code
0	[0]	[0]	aaaccc
1	[1]	[1]	aabccc
25	[25]	[25]	ccbccc
26	[1,0]	[0,1]	aaaaabccc
42	[1,16]	[16,1]	bcbaabccc
114	[4,10]	[10,4]	bababbccc

Labels

Labels are arbitrary abc strings (length must be a multiple of 3) followed by the ccc terminator.

Instruction Set

All instructions are 3-character abc sequences.

Code	Instruction	Params	Description
aaa	push	number	Push number onto current stack
aab	drop	-	Pop and discard top of stack
aac	swap	-	Swap top two elements
aba	dup	-	Duplicate top of stack
abb	rot	-	Rotate top three: [a,b,c] → [b,c,a]
abc	over	-	Copy top of other stack to current stack
aca	switch	-	Switch active stack (A ↔ B)
acb	pick	-	Copy nth element to top
acc	add	-	b + a (pop a, pop b, push b+a)
baa	sub	-	b - a
bab	mul	-	b * a
bac	div	-	b // a (integer division, truncate toward zero)
bba	mod	-	b % a (modulo)
bbb	not	-	Logical NOT: 0 → 1, non-zero → 0
bbc	load	-	Push register value onto stack
bca	store	-	Pop stack into register
bcb	readnum	-	Read integer from stdin, push onto stack
bcc	readchar	-	Read character (ASCII), push onto stack
caa	writenum	-	Pop and output integer
cab	writechar	-	Pop and output character (must be >= 0)
cac	jmp	label	Unconditional jump
cba	jz	label	Pop; if value == 0, jump
cbb	jn	label	Pop; if value < 0, jump
cbc	call	label	Call subroutine
cca	ret	-	Return from subroutine
ccb	label	name	Define label

IMPORTANT: Because the argument is popped first, 'pick' effectively behaves like a 1-based index from the original stack. The element is selected from the remaining stack.

Example:

[0, 1]  ->  push 2  ->  [0, 1, 2]
pick
1. pop 2   ->  [0, 1]
2. copy index 2  ->  [0, 1, 0]

Result: [0, 1, 0] (copied the bottom element)

Data Types

Integers: Arbitrary precision (Python int)

Characters: Unicode codes stored as integers

Labels: Strings of abc characters

Memory Model

Two Stacks

• Stack A and Stack B coexist
• One is active at any time
• switch toggles the active stack
• over copies the other stack's top to the current stack

Register

• Single register R stores one integer value
• load: push R onto current stack
• store: pop from current stack into R

Program Structure

Comments

Any character not a, b, or c is ignored (including spaces, newlines, and punctuation).

Program Termination

The program stops when it reaches the end of the source code (EOF). No explicit halt instruction is needed.

Labels

ccb aaa ccc      (define label "aaa")
cac aaa ccc      (jump to "aaa")

Parameters

• push: followed by a number (base-26 little-endian) then ccc
• jmp/jz/jn/call: followed by a label name then ccc
• label: followed by a label name then ccc

Examples

Hello, World!

aaacacaacccccabaaacbcabaccccabaaaabbabbccccabaaaabbabbccccabaaaacbabbccccabaaacaaaabccccabaaaacaaabccccabaaabaaabaccccabaaaacbabbccccabaaabababbccccabaaaabbabbccccabaaacbbabaccccabaaaacbaabccccab

Factorial

cacbbbcccccbaaacccabaaaaaaccccbaacbbccbcccababbcbabbcaaaaaabcccbaacacaaacccccbbbbcccbcbaaaaabcccbcacbcaaacccbbccaacacccacccccbccbcccccaccbccaccc

Fibonacci

cacbbbcccccbaaacccbbcaaaaabcccbaacbbccbcccaacaaaaaccccacbaccbbcaaaaabcccbaabcacacaaacccccbbbbcccbcbbcaaaaaaacccaaaaabccccbcaaacccaaccaacacccacccccbccbcccccaccbccacccccc

External Resources

• ABCLang Interpreter
• GitHub repository
• Online debugger