Palindrome

Context-free grammar for unary addition

S
=> 1S1
=> 11S11
=> 110S011
=> 1101S1011
=> 1101p1011
Accept

function delta(c, p) { // Unary addition
    if (c=='0' && p=='S') return "0S0";
    if (c=='1' && p=='S') return "1S1";
    if (c=='p' && p=='S') return "p";
    return '';  //default -- no transition
}
function generate(w, init='S') {
    //w: input String
    //init: start symbol
    //g: generated String
    let txt = init, g = init
    for (let i=0; i<w.length; i++) {
        let c = w[i], p = g[i]
        if (c == p) continue
        let d = delta(c, p)
        if (d == '') {
          input.selectionStart = i
          input.selectionEnd = i+1
          break
        }
        g = g.replace(p, d)
        txt += "\n=> "+g
    }
    return txt+'\n'+(w==g ? "Accept" : "Reject")
}