Functional JS implementation of Befunge Interpeter

befunge.js

const BEFUNGE = ()=>{

    var c, r;
    var s = [],
        i = 0,
        j = 0,
        di = 0,
        dj = 1,
        e = 0,
        set = (a,b)=>{di=b;dj=a},
        g = ()=>c[(i+=di) - di][(j+=dj)- dj];

    const I = {
        ">": () => set(1,0),
        "<": () => set(-1,0),
        "^": () => set(0,-1),
        "v": () => set(0,1),
        "?": () => ((x) => set(
                [0, [1,-1][(x > .75) | 0]][(x > .5) | 0],
                [0, [1,-1][(x > .25) | 0]][(x <= .5) | 0]
            ))(Math.random()),
        "+": () => s.push(s.pop() + s.pop()),
        "-": () => s.push(s.pop() - s.pop()),
        "*": () => s.push(s.pop() * s.pop()),
        "/": () => s.push((s.pop() / s.pop())|0),
        "%": () => s.push(s.pop() % s.pop()),
        "!": () => s.push((s.pop == 0)|0),
        "`": () => s.push(s.pop() > s.pop()),
        "_": () => set(-1 + 2*(s.pop()==0), 0),
        "|": () => set(0, -1 + 2*(s.pop()==0)),
        '"': () => {g(); while(c[i][j] != '"'){s.push(c[i][j].charCodeAt(0));g();}},
        ":": () => s.push(s[s.length-1] | 0),
        "\\": () => s = s.concat([s.pop(),s.pop()]),
        "$": () => s.pop(),
        ".": () => r+= s.pop(),
        ",": () => r+= String.fromCharCode(s.pop()),
        "#": () => g(),
        "g": () => s.push((c[s.pop()][s.pop()] || "").charCodeAt(0) | 0),
        "p": () => c[s.pop()][s.pop()] = String.fromCharCode(s.pop()),
        "&": () => s.push(prompt() | 0),
        "~": () => s.push(prompt().charCodeAt(0)),
        "@": () => e = 1,
        "0": () => s.push(0),
        "1": () => s.push(1),
        "2": () => s.push(2),
        "3": () => s.push(3),
        "4": () => s.push(4),
        "5": () => s.push(5),
        "6": () => s.push(6),
        "7": () => s.push(7),
        "8": () => s.push(8),
        "9": () => s.push(9),
        " ": () => {}
    }

    return (S)=> {
        c = S.split('\n').filter((x)=>x.length>0);
        r = "";
        while(!e) (I[c[i][j]](),g());
        return r;
    }
}

var b = BEFUNGE();
console.log(b(
`
>                                            v
v    "D"   <                                  
,          ^ $ " y"  <                        
,                    ^ $ " l" <               
,                             ^ $" a" <       
,                                     ^ "n " <
,                                             
>                                            v
v                  ,"is",                    <
                                              
     $$            >,v >,       $$           v
                   , $ \\                      
                   " " "                      
                                              
                   t h e                      
                                              
                   " " "                      
                     $                        
>                 ,^ >,^                      
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
v               " Illest "                   <
          ---------------------               
>                   :v                        
                  v:,_@                       
                  >  ^                        
                                              
        He's other things too, but
                 whatever
`));