Meander is a minimalistic esolang with only four instructions, created by Brian McPherson in 2014.
Programs are treated by the interpreter as being in the form of a one-dimensional tape, but are conceptually equivalent to being in the form of a two-dimensional surface of a tube created by curling the tape to form a spiral with a circumference of 80 cells. For convenience, programs are displayed two-dimensionally as 80-column lines of ASCII text characters.
Pointers have both a position and an angle, with the value of the angle determining how far and in which direction each pointer moves when advanced, emulating movement on a two-dimensional plane.
The instruction pointer is initially placed at the start of the program, and the data pointer is initially placed at the first cell after the end of the program, with both pointers having an initial angle of zero degrees.
All undefined cells have an initial value of zero. There is no input or output, except through direct access to the content of the memory cells.
When loading the source-code, interpreters should ignore all non-command characters, white-space and newline codes. The program-area of the "tape" should contain no non-command characters when the program begins.
|!||Rotate instruction pointer 45° clockwise|
|-||Rotate data pointer 90° clockwise|
|+||Increment value in cell at data pointer and advance data pointer|
|?||If value at data pointer is equal to 0 then rotate instruction pointer 90° clockwise, otherwise rotate instruction pointer 270° clockwise|
|Pointer Angle||Pointer advances by|
|0 degrees||+1 cells per move|
|45 degrees||+81 cells per move|
|90 degrees||+80 cells per move|
|135 degrees||+79 cells per move|
|180 degrees||-1 cells per move|
|225 degrees||-81 cells per move|
|270 degrees||-80 cells per move|
|315 degrees||-79 cells per move|