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Befunge-93 is a 2D stack-based esoteric programming language created by Chris Pressey in 1993 as a deliberate attempt to design a language as hard to compile as possible. Instead of executing top-to-bottom like a normal program, the instruction pointer moves in two dimensions across an 80×25 grid of characters, with each character being either a stack operation, an arithmetic op, or a direction-changing arrow (>, <, ^, v). Programs can also rewrite themselves at runtime via the 'p' (put) and 'g' (get) instructions, which is what makes Befunge famously uncompilable. Run Befunge programs in this online interpreter — no cfunge, fungify, or Funge-98 setup required.
"!dlroW ,olleH">:#,_@
How it executes:
"..." pushes characters onto the stack in REVERSE order
> turns the instruction pointer rightward
: duplicates the top of the stack
# skips the very next instruction
, pops and prints the top character
_ horizontal IF: pop, go LEFT if non-zero else RIGHT
@ end program
The loop prints each character of "Hello, World!\n" by
dupe-and-print, exiting the loop when the stack hits zero.Use Befunge-93 for code-golf challenges, esolang competitions on sites like Code Golf Stack Exchange and anarchy golf, teaching unconventional control flow, mind-bending puzzle programming, and as a gateway to other 'fungeoid' languages (Funge-98, Befunge++, Cardinal, Trefunge). Befunge-93's 2D execution model is also a useful teaching tool for explaining why most modern languages chose 1D top-to-bottom execution — and what you give up by using a deliberately weird alternative.
It pioneered the 2D programming language concept and was specifically designed to be uncompilable — the 'p' instruction lets a program rewrite its own source mid-execution, so the only way to know what a program will do is to actually run it. This makes Befunge unusually loved by esoteric-language researchers, code golfers, and compiler-theory students who use it as a counter-example for static analysis.
Befunge-93 uses a fixed 80×25 character playfield (the same dimensions as a classic VT100 terminal screen). The instruction pointer wraps around when it falls off an edge. Befunge-98 (the later spec) lifted this to an arbitrary-sized grid, but Befunge-93 keeps the original constraint and is what most online interpreters implement by default.
> sends the pointer right, < left, ^ up, v down, and ? picks a random direction. _ is the horizontal IF: pop the stack, go right if zero else left. | is the vertical version. # skips the next instruction. @ ends the program. Everything else is either a digit (push 0-9), an arithmetic op (+ - * / %), or a stack manipulator (: dup, \ swap, $ pop, p put, g get).
main.bfplain text — no highlighter ships for this language~ or &>25*"!dlroW olleH",,,@