public static Tuple <Semantics.SExp, String> parseSExp(String s)
{
var t = s.Trim();
if (t.Length > 0 && t[0] == '(')
{
var l = new List <Semantics.SExp>();
var m = s.Substring(1).Trim();
var r = parse(m);
while (r != null)
{
l.Add(r.Item1);
m = r.Item2.Trim();
r = parse(r.Item2);
}
if (m.Length > 0 && m[0] == ')')
{
Semantics.SExp acc = new Semantics.Atom("nil");
for (int i = l.Count - 1; i >= 0; i--)
{
acc = new Semantics.Cons(l[i], acc);
}
return(Tuple.Create(acc, m.Substring(1).Trim()));
}
else
{
return(null);
}
}
else
{
return(null);
}
}
public static Tuple <Semantics.SExp, String> parseAtom(String s)
{
var t = s.Trim();
var i = 0;
if (t.Length > 0 && (t[0] == '(' || t[0] == ')'))
{
return(null);
}
while (t.Length > i && t[i] != ' ' && t[i] != '(' && t[i] != ')')
{
i++;
}
if (i == 0)
{
return(null);
}
Semantics.SExp r = new Semantics.Atom(t.Substring(0, i));
var m = t.Substring(i);
return(Tuple.Create(r, m));
}
