/// <summary>
/// Convert infix regexp re to postfix notation.
/// Insert . as explicit concatenation operator.
/// </summary>
/// <param name="re">input re</param>
/// <returns>postfix re</returns>
private static string re2post(string re)
{
int nalt = 0;
int natom = 0;
string buf = "";
var dst = new StringBuilder();
var paren = new List <paren>();
var p = new paren();
paren.Add(p);
foreach (var r in re)
{
switch (r)
{
case '(':
if (natom > 1)
{
--natom;
dst.Append('.');
}
p.nalt = nalt;
p.natom = natom;
p = new paren();
paren.Add(p);
nalt = 0;
natom = 0;
break;
case '|':
if (natom == 0)
{
throw new Exception("unexpected |");
}
while (--natom > 0)
{
dst.Append('.');
}
nalt++;
break;
case ')':
if (p.Equals(paren[0]))
{
throw new Exception("something bad");
}
if (natom == 0)
{
throw new Exception("unexpected )");
}
while (--natom > 0)
{
dst.Append('.');
}
for (; nalt > 0; nalt--)
{
dst.Append('|');
}
paren.Remove(p);
p = paren.Last();
nalt = p.nalt;
natom = p.natom;
natom++;
break;
case '*':
case '+':
case '?':
if (natom == 0)
{
throw new Exception("unexpected " + r);
}
dst.Append(r);
break;
default:
if (natom > 1)
{
--natom;
dst.Append('.');
}
dst.Append(r);
natom++;
break;
}
}
if (p.Equals(paren.Last()) != true)
{
throw new Exception("unbalanced parens");
}
while (--natom > 0)
{
dst.Append('.');
}
for (; nalt > 0; nalt--)
{
dst.Append('|');
}
return(dst.ToString());
}
=> new OptionalRule(paren(delimit(r.r1, r.r2)));
