|Designed by||Chris Pressey|
|Computational class||Turing complete (Befunge-98)|
- 1 History
- 2 Etymology
- 3 Language overview
- 4 Instructions
- 5 Computational class
- 6 Compilation
- 7 Examples
- 8 Interpreters
- 9 Related languages
- 10 External resources
Befunge is believed to be the first two-dimensional, ASCII-based, general-purpose (in the sense of "you could plausibly write Hunt the Wumpus in it" ) programming language. Its form was influenced in part by the multimedia scripting application AmigaVision, and in part by Forth.
The original Befunge (known as "Befunge-93" to distinguish it from others) has spawned many descendants and remote cousins. The closest relative, and most direct extension, of Befunge-93 is Befunge-98 of the Funge-98 family of languages. Each Funge extends the central concepts of Befunge to a given number of dimensions (for example, Unefunge is one-dimensional, Trefunge is three-dimensional, Nefunge is n-dimensional, etc.).
The word "Befunge" started life as a typographical error for the word "before", typed by Curtis Coleman at 4AM on a BBS chat system.
It was then reverse-endowed with a fictional morphology where it took on the meaning Be- (a corruption of the prefix bi-, for "two") + funge (fictional root of the word fungible, i.e. "interchangeable"). That is, to interchange (program codes with data) in two (dimensions).
The name is pronounced /bee-FUNJ/.
A Befunge program consists of a two-dimensional playfield of fixed size. The playfield is initially loaded with the instructions of the program. It also doubles as an updateable storage unit.
Execution proceeds by the means of a program counter (-93) or instruction pointer (-98). The instruction pointer begins at a set location (the upper-left corner of the playfield) and is initially travelling in a set direction (right). As it encounters instructions, they are executed. The instructions may have an effect on the instruction pointer's direction and position (-98 only). The following, for example, is literally an infinite loop:
Instructions may also affect the contents of a stack in the manner of Forth.
Befunge-93 has the following commands:
||Addition: Pop two values a and b, then push the result of a+b|
||Subtraction: Pop two values a and b, then push the result of b-a|
||Multiplication: Pop two values a and b, then push the result of a*b|
||Integer division: Pop two values a and b, then push the result of b/a, rounded down. According to the specifications, if a is zero, ask the user what result they want.|
||Modulo: Pop two values a and b, then push the remainder of the integer division of b/a.|
||Logical NOT: Pop a value. If the value is zero, push 1; otherwise, push zero.|
||Greater than: Pop two values a and b, then push 1 if b>a, otherwise zero.|
||PC direction right|
||PC direction left|
||PC direction up|
||PC direction down|
||Random PC direction|
||Horizontal IF: pop a value; set direction to right if value=0, set to left otherwise|
||Vertical IF: pop a value; set direction to down if value=0, set to up otherwise|
||Toggle stringmode (push each character's ASCII value all the way up to the next |
||Duplicate top stack value|
||Swap top stack values|
||Pop (remove) top stack value and discard|
||Pop top of stack and output as integer|
||Pop top of stack and output as ASCII character|
||Bridge: jump over next command in the current direction of the current PC|
||A "get" call (a way to retrieve data in storage). Pop two values y and x, then push the ASCII value of the character at that position in the program. If (x,y) is out of bounds, push 0|
||A "put" call (a way to store a value for later use). Pop three values y, x and v, then change the character at the position (x,y) in the program to the character with ASCII value v|
||Get integer from user and push it|
||Get character from user and push it|
||Push corresponding number onto the stack|
Because Befunge-93 programs are given an explicit limit of 80x25 cells on the size of their playfield, but are also given a working stack, any Befunge-93 program should be simulatable by a push-down automaton.
However, the converse is not true; there surely exist some push-down automata which cannot be simulated by any Befunge-93 program (because they contain more states than can be encoded in the 80x25 playfield).
Befunge-98 removes the fixed-size restriction on the playfield, and thus should be Turing-complete.
As stated, the design goal for Befunge was to create a language which was difficult to compile. This was realized by two main features:
- self-modifying – the
pinstruction can write new instructions into the playfield; and
- multi-dimensional – the same instruction can be executed in four different contexts (in a left-to-right series of instructions, or right-to-left, or upward or downward.)
Nevertheless, these obstacles have been overcome to some degree, and Befunge compilers have been written, using appropriate techniques.
The bf2c compiler included with the standard Befunge-93 distribution uses threaded code: each instruction is compiled to a snippet of C code, and control flows through the snippets just as it does in a Befunge interpreter (that is, conditionally on the value of some 'direction' register.) This does not result in a significant advantage over a good interpreter. Note that the bf2c compiler is not correct since it does not handle
p correctly, but it would not be impossible to make it do so (although the C language might not be well-suited for this.)
The Betty compiler, for example, treats every possible straight line of instructions as a subprogram, and if a
p instruction alters that subprogram, that subprogram is recompiled. This is an interesting variation on just-in-time compilation, and it results in a much better advantage over an interpreter, since many instructions can be executed in native code without making intervening decisions on the 'direction' register.
The Befunjit and Bejit compilers, similarly to the Betty compiler, split the original code into subprograms which are lazily compiled and executed. They, however, divide the original playfield into "static paths" - code paths which do not contain instructions that conditionally change direction (i.e.
?). The "static paths" may span on more cells than the "straight line paths" of Betty, which results in fewer and longer subprograms. Thus, there are fewer context jumps between the compiler and the compiled code and allows more optimisations.
There are also programs which combine a Befunge interpreter and a copy of a given Befunge program into a single executable which runs the Befunge program when started. For Befunge-93 this can easily be done by having a preallocated 80×25 cell storage space in the interpreter, and filling it in with the chosen Befunge program. This might be considered a sort of pathological version of threaded code, and while it produces a similar effect to a compiler, that is, it generates a "native executable", it is not really considered the same thing. Sometimes such a tool is called a pseudo-compiler or linker. TBC (Tim's Befunge Compiler), and BFC (BeFunge Compiler) written by Uranium-239, are examples of such tools.
&>:1-:v v *_$.@ ^ _$>\:^
Sieve of Eratosthenes
2>:3g" "-!v\ g30 < |!`"O":+1_:.:03p>03g+:"O"`| @ ^ p3\" ":< 2 234567890123456789012345678901234567890123456789012345678901234567890123456789
01->1# +# :# 0# g# ,# :# 5# 8# *# 4# +# -# _@
0v "<@_ #! #: #,<*2-1*92,*25,+*92*4*55.0
Simple game ("Less or More")
vv < < 2 ^ v< v1<?>3v4 ^ ^ > >?> ?>5^ v v v9<?>7v6 v v< 8 > > ^ vv < < 2 ^ v< v1<?>3v4 ^ ^ > >?> ?>5^ v v v ,*25 << v9<?>7v6 ,, v v< "" 8 >< > > ^ ""v >*:.>0"!rebmun tupnI">:#,_$25*,:&:99p`|^< _0"!niw uoY">:#,_$25*,@ ^ < >:99g01-*+^
>78*vD v$_#>vN 7#!@ A 3 :v??v 9,-"""" 4+1ACGT +,,"""" >^^<<<<
It will fail if you use the 'g' or 'p' function outside the 80x20 playfield. However, you can use them outside this range if the size of your code is greater.
Module Module1 Sub Main() Console.WriteLine("Befunge Inteper By BlackCap") Console.Write("filepath> ") Dim code = FixLines(IO.File.ReadAllText(Console.ReadLine, Text.Encoding.Default)) Dim Stack As New Stack(Of Integer) Dim StringMode, SkipNext As Boolean Dim xCur, yCur, dir As Integer Dim g = Function(i%) If(Stack.Count <= i, 0, Stack(i)) Dim pop = Function() If(Stack.Count > 0, Stack.Pop, 0) Do If xCur < 0 OrElse yCur < 0 OrElse xCur >= code(0).Length OrElse yCur >= code.Length Then Select Case dir Case Is = 0 : xCur = 0 Case Is = 1 : yCur = 0 Case Is = 2 : xCur = code(0).Length - 1 Case Is = 3 : yCur = code.Length - 1 End Select End If Dim c As Char = code(yCur)(xCur) If SkipNext Then SkipNext = False Else If StringMode Then If c = Chr(34) Then StringMode = False Else Stack.Push(AscW(c)) Else Select Case c Case Is = "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" : Stack.Push(Val(c)) ' Diggits Case Is = "@" : Exit Do ' Terminate Case Is = "$" : pop() ' Pop Case Is = ":":Stack.Push(g(0)) ' Dupe Case Is = "\" ' Swap Dim a = pop(), b = pop() Stack.Push(a) : Stack.Push(b) Case Is = "+", "-", "*", "/", "%" ' Math Dim a = pop(), b = pop() Stack.Push(If(c = "+", b + a, If(c = "-", b - a, If(c = "*", b * a, If(c = "/", b / a, b Mod a))))) Case Is = Chr(34) : StringMode = True ' StringMode Case Is = "!" : Stack.Push(If(pop() = 0, 1, 0)) ' Not Case Is = "`" ' Greater Dim a = pop(), b = pop() Stack.Push(If(b > a, 1, 0)) Case Is = "." : Console.Write(pop()) ' Output int Case Is = "," : Console.Write(ChrW(pop())) ' Output ASCII Case Is = "~" ' Read single char Console.Write(vbCrLf & vbCrLf & "> ") Stack.Push(AscW(Console.ReadKey.KeyChar)) Case Is = "&" ' Read a line Console.Write(vbCrLf & vbCrLf & "=> ") Array.ForEach(Console.ReadLine.ToArray, Sub(x As Char) Stack.Push(AscW(x))) Case Is = "#" : SkipNext = True ' Skip Case Is = ">", "v", "<", "^" : dir = ">v<^".IndexOf(c) ' Change direction Case Is = "_" : dir = (pop() <> 0) * -2 ' Hor if Case Is = "|" : dir = 1 + (pop() <> 0) * -2 ' Ver if Case Is = "?" ' Random direction Static R As New Random dir = R.Next(0, 4) Case Is = "g" ' Get Dim y = pop(), x = pop() Stack.Push(AscW(code(y)(x))) Case Is = "p" ' Put Dim y = pop(), x = pop(), val = pop() code(y) = code(y).Remove(x) & ChrW(val) & code(y).Substring(x + 1) End Select End If End If Select Case dir Case Is = 0 : xCur += 1 ' Right Case Is = 1 : yCur += 1 ' Down Case Is = 2 : xCur -= 1 ' Left Case Is = 3 : yCur -= 1 ' Up End Select Loop Console.WriteLine(vbCrLf & vbCrLf & "The program was terminated" & vbCrLf & "Press any key to exit") Console.ReadKey() End Sub Function FixLines(str As String) As String() Dim lines = Split(str, vbCrLf).ToList Dim l% = Math.Max((From a In lines Order By a.Length).Last.Length, 80) For i = lines.Count To 20 lines.Add("") Next For i = 0 To lines.Count - 1 For i2 = lines(i).Length + 1 To l lines(i) &= " " Next Next Return lines.ToArray End Function End Module
It only understands the befunge-93 instruction set but can work with program sizes greater than 80x25.
On a standard computer it can reach about 6000 kHz interpretation speed.
It has advanced features like
- stepping the instruction pointer backwards
- showing a graph of the possible program flow paths
- context-aware syntax highlighting
- supporting programs with extended size (tested with an 2000x12039 program)
Befunge was preceded in 1991 by a similar but less featureful language Biota, which was designed for experiments in self-reproduction. It was followed soon after, in 1994, by another similar language, Orthagonal, the design of which was spurred by a discussion on alt.folklore.computers. Each of these three languages originated (as far as anyone can tell) completely independently of the other two.
Befunge has also provided inspiration to the design of subsequent languages, the most similar of these are known as fungeoids. Most of the languages are not similar enough to be called direct descendants, but often the author mentions the influence of Befunge in the accompanying commentary. Such languages include Wierd, a two-dimensional Turing tarpit; Befreak, a reversible language; and PATH, which combines in elements of Brainfuck.
- Befunge-93 documentation.
- Befunge-93 Online Compilation.
- befungee, a Befunge-93 interpreter written in python, with a debugger and a concurrent mode.
- Bephunge, an implementation of Befunge-93 in PHP (command-line) (mirror in the Esoteric File Archive).
- Befunge programs in the Esoteric File Archive.
- YaBI93 - multiplatform Befunge93 interpreter (with IDE) for Java 1.5.
- Marsh/Bejit A fast interpreter and a quasi JIT.
- Befunjit - A just-in-time compiler for Befunge-93
- awkfunge Befunge-93 interpreter written in AWK.
- FungePP Interpreter for Funge++, a Procedural Befunge-93 Extension, written in C++
- BefunCompile a restricted Befunge-93 to C (and C#, and Python) compiler
Befunge-98 and beyond
- Funge-98 documentation.
- Funge-98 specification
- vsync's Funge stuff.
- BefungeSharp A Funge-98 IDE being written in C#. Designed to have a strong editor and a complaint interpreter. Currently in development and well supported by its author.
- Fungus (from the Wayback Machine; retrieved on 22 March 2007) - a nice Befunge-98 IDE for Win32. Warning: its interperter is not fully standards compliant.
- BeQunge A cross-platform Funge-98 interpreter, code editor, and debugger. Works in any number of dimensions.
- J^4: Befunge Jeffrey Lee's Befunge site, features plenty of interesting programs.
- Mycology and CCBI A complete Befunge-98 test suite based on the specification, and an interpreter which passes all the tests.
- cfunge - Small fast Befunge-98 interpreter in C, standard compliant.
- Sponge - a compiler (in Common Lisp) from a tiny subset of Scheme to Befunge 98.
- PyFunge - A Befunge-93/Funge-98 interpreter in Python. Its goal is a fully functional, compliant and optimizing implementation of Funge-98.
- Fungi - A standards compliant Funge-98 interpreter and debugger written in Haskell.
- Closidrium - Author retrospective of creating a Befunge-98 Interpreter in Clojure.
- Multilang - A shell supporting multiple languages, including Befunge-98.
- BefunGen - A Befunge compiler / code generator, compiles to Befunge code from a c-like language
- Fungewars - A programming game in Funge-98.