Blacktime
Blacktime is a Whitespace derivative designed and originally implemented in 2014 by Three If By Whiskey. It was inspired by the realization that Whitespace's 24 distinct operations would map very well into a system of encoding instructions as times.
Contents
Syntax
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Blacktime programs are composed entirely of spaces (' '), underscores ('_'), vertical pipes (''), and line breaks. Instructions are written as contiguous groups of four sevensegment displays, representing either a complete 24hour time or a "time delta", explained below. There are no syntax errors; if the character in a given position is not the underscore or pipe expected for that position, it is simply ignored.
Evaluation
The initial instruction in a Blacktime program (the "seed") must be a complete, zeropadded, 24hour time. Each subsequent instruction is a "time delta" whose segments are XOR'd with the previous time's to produce the current time. It is a runtime error, and program execution terminates, if at any point an invalid time is generated by this process.
The previous hour is subtracted from the current, and this value (modulo 24, with the result taking the sign of the divisor) indicates which operation to perform. This same calculation is applied to the minutes (modulo 60) to produce the argument supplied to the operation, if applicable.
Operations
The first eight operations are the ones which take an argument, denoted as n in their descriptions.
Opcode  Name  Description 

0  push 
Place n at the top of the stack. 
1  copy 
Place at the top of the stack the value n levels deep, such that copy 0 is a synonym for dup .

2  slide 
Remove the n values beneath the top of the stack. 
3  label 
Create a label called n, to be used as a jump target. 
4  call 
Call the "subroutine" starting at label n; a subsequent ret will resume execution from the point of this call.

5  jump 
Jump to label n. 
6  jz 
Remove the value at the top of the stack and jump to label n if it was 0. 
7  jn 
″ if it was negative. 
8  pop 
Remove the value at the top of the stack. 
9  dup 
Duplicate the value at the top of the stack. 
10  swap 
Swap the two values at the top of the stack. 
11  add 
Remove the two values at the top of the stack and push back their sum. 
12  sub 
″ difference. 
13  mul 
″ product. 
14  div 
″ quotient. 
15  mod 
″ remainder. 
16  store 
Remove the two values at the top of the stack and store the first in the heap at the address indicated by the second. 
17  load 
Replace the value at the top of the stack with the value at the indicated heap address. 
18  ret 
Return from a call operation.

19  ichr 
Place at the top of the stack the value of a usersupplied character. 
20  inum 
″ number. 
21  ochr 
Remove the value at the top of the stack and output its value as a character. 
22  onum 
″ number. 
23  exit 
Terminate program execution, perhaps prematurely. 
Example programs
Hello, world!
_ _ _ _ _ _ _ _ _ _ _ __   _ _ _  _ _ _ _ _ _ _ _    _  _ _ _ _ _ _ _ _ _ _ _ _ _  _   _ _ _ _  _ _  _  _ _  __ _ _ _ _ _   _ _ _ _ _ _ _ _ _ _ _   _    _    _    _ _ _  _   _ __  _ _   _ _ _ _ _ _ _ _ _ _ _    _     _    _ _    _  _  _ _  _ _ _ _ _ _ _ _ _   _ _ _ _   _ _  _  _ 
Cat
_ _ _ `push 0` operations _ _   __  are good places to _ _ _ _   _ _ store commentary.  _  _ _ _ _ _ _     _ _   _ _ _  _    _ _
Computational class
Because it is possible to interpret brainfuck in Whitespace, Blacktime is trivially Turingcomplete.