How to compile a program in Befunge-93?

Question

How do I save and compile a program in Befunge-93? What file extension do I need to save the file as (like fileName.what)? Then how do I compile it?

Answer 1

Befunge is typically an interpreted language. In fact it was designed to be difficult to compile because the programs are self-modifying (but that hasn't stopped people from trying to write a compiler).

You should save the file however you like (a .bf extension is typically used) and run the interpreter (bef), passing the filename as a command line argument.

You can see the usage instructions in the source code for the interpreter.

Answer 2

As it is an interpreted language, it usually won't be compiled. A C# Befunge 93 interpreter below, that will read code as an array[] of strings.

string befunge93(string[] p) {
for (int i=0;i<p.Length;i++)
    p[i]=p[i].Replace("\"","ª"); // REMOVE QUOTATIONS TO MAKE THINGS EASIER
int l=0; int c=0; // current line and colum
var stack=new Stack<int>(new int[20000]); // initialize stack with many zeroes. 
string res=""; // output limited to 1000 chars
int limit=100000; // max commands limited to 10^5 
bool smode=false; // string mode
char direction='>';
//-------- MAIN LOOP ---------------
while (res.Length < 1000 && limit--> 0  )
    {
    var ch=p[l][c];
    if (ch=='ª') // ", TOGGLE STRING MODE
        smode = !smode;
    else if (smode) // STRING MODE => PUSH CHAR
        stack.Push((int)ch);
    else if (ch==',') // OUTPUT CHAR FROM STACK
        res+=(char)stack.Pop();
    else if (new Regex(@"[><^v]").IsMatch(""+ch)) // CHANGE DIRECTION
        direction = ch; 
    else if (new Regex(@"\d").IsMatch(""+ch)) // CHANGE DIRECTION
        stack.Push(ch-'0'); 
    else if (ch=='*') // MULTIPLICATION
        stack.Push(stack.Pop()*stack.Pop());
    else if (ch=='+') // SUM
        stack.Push(stack.Pop()+stack.Pop());
    else if (ch=='`') // GREATER THEN
         stack.Push(stack.Pop()>=stack.Pop()?0:1); 
    else if (ch=='!') // NOT
        stack.Push(stack.Pop()==0?1:0);
    else if (ch=='.') // OUTPUT NUMBER
        res+=$"{stack.Pop()} ";
    else if (ch=='#') // JUMP NEXT COMMAND
        move();
    else if (ch=='$') // DISCARD ITEM FROM STACK
        stack.Pop();
    else if (ch=='\\') // SWAP
        { var a=stack.Pop(); var b=stack.Pop(); stack.Push(a); stack.Push(b); }
    else if (ch=='%') // modulo
        { var a=stack.Pop(); var b=stack.Pop(); stack.Push(b%a); }
    else if (ch=='-') // MINUS
        { var a=stack.Pop(); var b=stack.Pop(); stack.Push(b-a); }
    else if (ch=='/') // DIVISION
        { var a=stack.Pop(); var b=stack.Pop(); stack.Push(b/a); }
    else if (ch==':') // DUPLICATE
        stack.Push(stack.First());
    else if (ch=='_' || ch=='|') // CONDITIONALS: MOVE IF STACK ZERO, LEFT OTHERWISE
        {
        var last = stack.Pop();
        if (ch=='_') direction=last==0?'>':'<'; // right if stack was zero. Left otherwise
        else direction=last==0?'v':'^'; // ch=='|'  
        }
    else if (ch==' '); // SPACE - DO NOTHING. 
    else return res;
    move();
    }
return res;
void move() // move cursor
{
    switch(direction)
        {
            case '>':
                if (++c==p[0].Length) c=0; break;
            case '<':
                if (--c==-1) c=p[0].Length-1; break;
            case 'v':
                if (++l==p.Length) l=0; break;
            case '^':
                if (--l==-1) l=p.Length-1; break;
            default: break;
        }
}
}