Halforth

Halforth - is an esolang based on Forth by User:ChuckEsoteric08 in which every instruction takes half of a byte (a single hexadecimal digit)

Description

Language works on a stack as well as a tape to store data, which could contain both negative and positive integers

Commands (in hex)

Command	Opcode	Description
0-9	push x	Push a single digit to the stack
A	op	pop operation, a and b and perform b<op>a (see below)
B	if	Pop a value, and start if nonzero block
C	dup	Duplicates top of the stack
D	endif	End if block
E	define / ;	Pop a value of and start a procedure definition with that name, which is finished by another E
F	exec	Pop a value and execute a procedure with that name

There is four I/O related procedures which could be executed with and F:

Procedure name	Opcode	Description
0	out	Pop element from the stack and output it as a number
1	cout	Pop element from the stack and output it as a character
2	in	Input a number and push it to the stack
3	cin	Input a character and push it's value in the stack

Instructuon A performs operation on the elements using a value of the element above them:

Value	Opcode	Operation
0	add	Addition
1	sub	Subtraction
2	mul	Multiplication
3	div	Division
4	less	Less than
5	eq	Equals
7	bigger	Bigger than
8	swap	Swap instruction, pushes b and then a
9	store	Store value a at index b
10	load	Push a back, and then load value from index b and push it to the stack