public static ErlangNumberToken Lex(TextBuffer buffer)
{
var sb = new StringBuilder();
sb.Append(buffer.Peek());
buffer.Advance();
bool seenHash = false;
bool seenE = false;
bool seenDecimal = false;
var last = default(char);
while (buffer.TextRemains())
{
var c = buffer.Peek();
if (c == '#')
{
if (!seenHash && !seenDecimal)
{
seenHash = true;
buffer.Advance();
sb.Append(c);
}
else
{
// premature end of number
break;
}
}
else if (c == '.')
{
if (!seenDecimal && !seenHash)
{
seenDecimal = true;
buffer.Advance();
sb.Append(c);
}
else
{
// premature end of number
break;
}
}
else if ((c == 'e' || c == 'E') && !seenHash)
{
if (!seenE)
{
seenE = true;
buffer.Advance();
sb.Append(c);
}
else
{
// premature end of number
break;
}
}
else if (c == '+' || c == '-')
{
if (seenE && (last == 'e' || last == 'E'))
{
buffer.Advance();
sb.Append(c);
}
else
{
// possibly already saw sign
break;
}
}
else if (IsNumberContinue(c))
{
buffer.Advance();
sb.Append(c);
}
else
{
break;
}
last = c;
}
Debug.Assert(!(seenDecimal && seenHash)); // should not have seen both
Debug.Assert(!(seenE && seenHash)); // should not have seen both
if (last == '.')
{
// numbers can't end in a decimal point
buffer.Retreat();
sb.Remove(sb.Length - 1, 1);
seenDecimal = false;
}
var text = sb.ToString();
double doubleValue = default(double);
BigInteger bigValue = default(BigInteger);
string error = null;
if (!seenHash)
{
// simple parsing
if (seenDecimal || seenE)
{
doubleValue = Convert.ToDouble(text);
}
else
{
bigValue = BigInteger.Parse(text);
}
}
else
{
// complex hash parsing
var parts = text.Split("#".ToCharArray(), 2);
int @base = Convert.ToInt32(parts[0]);
if (@base >= 2 && @base <= 36)
{
int val = 0;
for (int i = 0; i < parts[1].Length; i++)
{
int digitValue = 0;
var l = parts[1][i];
if (l >= '0' && l <= '9')
{
digitValue = l - '0';
}
else
{
digitValue = char.ToUpperInvariant(l) - 'A' + 10;
}
if (digitValue < 0 || digitValue >= @base)
{
error = string.Format("Digit '{0}' not valid for base '{1}'", l, @base);
return(new ErlangNumberToken(text)
{
Error = error
});
}
val = (val * @base) + digitValue;
}
bigValue = val;
}
else
{
error = "Base must be between 2 and 36 inclusive.";
}
}
if (seenDecimal)
{
return new ErlangNumberToken(text, doubleValue)
{
Error = error
}
}
;
else
{
return new ErlangNumberToken(text, bigValue)
{
Error = error
}
};
}
}