Tact

Tact

Paradigm(s)	imperative, stack-based
Designed by	User:Las-r
Appeared in	2026
Computational class	Turing complete
Reference implementation	GitHub
File extension(s)	.tc

Tact is a stack-based esoteric programming language created by Nayif Ehan in 2026.

Concepts

Tact programs consist of a single string of characters executed sequentially from left to right. The program halts automatically when the instruction pointer moves past the end of the source string.

Stack

Tact operates on a single standard stack of integers. Any attempt to pop or inspect an element from an empty stack results in an immediate interpreter crash due to a lack of bounds checking.

Pointer

The instruction pointer tracks the index of the character currently being executed, starting at index 0. Control flow is handled by dynamically setting or incrementing this pointer based on top-of-stack values.

Syntax

Symbol	Name	Action
0–9	Push digit	Push that digit onto the stack
*	Times ten	Pop a, push a × 10 (used to build multi-digit numbers)
+	Add	Pop a, b, push a + b
-	Subtract	Pop a, b, push b - a (second-popped minus first-popped)
d	Duplicate	Push a copy of the top element
x	Discard	Pop and discard the top element
s	Swap	Swap the top two elements
o	Over	Push a copy of the second-from-top element
r	Rotate	Rotates the top 3 elements, i.e. brings the third element to the top
j	Jump	Pop n, set instruction pointer to index n
>	Skip-if-positive	Pop n; if n > 0 continue normally, else skip the next instruction
<	Skip-if-negative	Pop n; if n < 0 continue normally, else skip the next instruction
i	Input	Read an integer from user input and push it
p	Print	Print the top of stack without popping

Examples

Note: An in-place variation works directly with the numbers at the top of the stack, acting as a sort of operation itself.

Countdown

ipd1-s1s>j

Nth Triangular Number

0iso+s1-d2s>jxxp

Multiplication

0iisro+sr1-d3s>jxxxp

In-place variation: 0rrsro+sr1-d3s>jxxx

Factorial

1id1-2*s>jxxp9*j0x0xd1-rr0rr0xsro+sr1-d3*s>jxxxs2j