flag is an esolang created by User:None1. The interesting thing about this esolang is that tabs are disallowed (vertical tabs are considered tabs, too).
flag's syntax is:
flag should be empty or contains only spaces.
flag has its data stored in a bounded tape with 8 bit cells.
There is also a pointer, which points to the origin in the beginning.
All cells shound be 0 in the beginning
Any character (except tab) is considered an opcode in flag. However, there are 2 types of opcode - Special opcode and Ordinary opcode.
? Reads a character from standard input and overwrites the cell the pointer is pointing at with it. (The user should not enter tab, otherwise the program should raise an error and quit.)
! Prints the character the pointet is pointing at, if the character is a tab, raise an error and quit.
: Moves the pointer to the cell left of it.
; Moves the pointer to the cell right of it.
_ Makes the character after it an ordinary opcode even if it is a special opcode (tabs are still disallowed).
ordinary opcodes are legal characters that are npt.considered special opcodes, these characters are directly printed to standard output when executed.
Tab is considered an illegal character in flag, and flag programs which have tabs should not be allowed.
Flag consists of only spaces, each line of flag programs should have only one flag. Flag controls how many times the code is executed.
N is the length of flag N times 0 once 1 ∞ (infinity) 2 The code is executed repeatedly until the pointer points at 0. (just like Brainfuck's brackets) >2 N-1 times
Hello World program:
In fact, any program without linefeeds and tabs and special opcodes, and does not begin with a space can be a quine. That means flag has infinite number of quines.
The repository of flag, where the standard interpreter of flag is at.