Pop S-Expression

function pop(input) {
	var i = input.indexOf('(') + 1, // Start of out outermost s-expression
		j = -1,                     // Will be set to the index of the matching ) to close the outsermost s-expression
		l = 1,                      // Nesting 'stack counter' to make sure we get the outermost expression only
		k = 0;                      // Loop index

	if(i < 0)
		return input;

	for(k=i; k<input.length; k++) {
		if(input[k] === '(') {
			l += 1;
		} else if(input[k] === ')') {
			l -= 1;
		}
		
		if(l === 0) {
			j = k;
			break;
		}
	}

	if(j < 0)
		return input;

	//first s-expression, after first s-expression
	return [input.slice(0,i-1), input.slice(i,j), input.slice(j+1)];
}