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// $Id$
using System;
using System.Text;
using System.IO;
namespace Lisp {
public class Lexer {
private StreamReader stream;
private char[] buffer;
private char c;
int bufpos;
int buflen;
public class EOFException : Exception {
};
public enum TokenType {
EOF,
OPEN_PAREN,
CLOSE_PAREN,
SYMBOL,
STRING,
INTEGER,
REAL,
TRUE,
FALSE
};
private StringBuilder TokenStringBuilder;
public string TokenString {
get { return TokenStringBuilder.ToString(); }
}
public int LineNumber;
public Lexer(StreamReader stream) {
this.stream = stream;
buffer = new char[1025];
NextChar();
}
public TokenType GetNextToken() {
try {
while(Char.IsWhiteSpace(c)) {
NextChar();
if(c == '\n')
LineNumber++;
}
TokenStringBuilder = new StringBuilder();
switch(c) {
case ';': // comment
while(true) {
NextChar();
if(c == '\n') {
LineNumber++;
break;
}
}
NextChar();
return GetNextToken();
case '(':
NextChar();
return TokenType.OPEN_PAREN;
case ')':
NextChar();
return TokenType.CLOSE_PAREN;
case '"': { // string
int startline = LineNumber;
while(true) {
NextChar();
if(c == '"')
break;
if(c == '\\') {
NextChar();
switch(c) {
case 'n':
c = '\n';
break;
case 't':
c = '\t';
break;
}
}
TokenStringBuilder.Append(c);
}
NextChar();
return TokenType.STRING;
}
case '#': // constant
NextChar();
while(Char.IsLetterOrDigit(c) || c == '_') {
TokenStringBuilder.Append(c);
NextChar();
}
if(TokenString == "t")
return TokenType.TRUE;
if(TokenString == "f")
return TokenType.FALSE;
throw new Exception("Unknown constant '"
+ TokenString + "'");
default:
if(Char.IsDigit(c) || c == '-') {
bool have_nondigits = false;
bool have_digits = false;
int have_floating_point = 0;
do {
if(Char.IsDigit(c))
have_digits = true;
else if(c == '.')
have_floating_point++;
else if(Char.IsLetter(c) || c == '_')
have_nondigits = true;
TokenStringBuilder.Append(c);
NextChar();
} while(!Char.IsWhiteSpace(c) && c != '\"' && c != '('
&& c != ')' && c != ';');
if(have_nondigits || !have_digits
|| have_floating_point > 1)
return TokenType.SYMBOL;
else if(have_floating_point == 1)
return TokenType.REAL;
else
return TokenType.INTEGER;
} else {
do {
TokenStringBuilder.Append(c);
NextChar();
} while(!Char.IsWhiteSpace(c) && c != '\"' && c != '('
&& c != ')' && c != ';');
return TokenType.SYMBOL;
}
}
} catch(EOFException) {
return TokenType.EOF;
}
}
private void NextChar() {
if(bufpos >= buflen) {
if(!stream.BaseStream.CanRead)
throw new EOFException();
buflen = stream.Read(buffer, 0, 1024);
bufpos = 0;
// following hack appends an additional ' ' at the end of the file
// to avoid problems when parsing symbols/elements and a sudden EOF:
// This way we can avoid the need for an unget function.
if(!stream.BaseStream.CanRead) {
buffer[buflen] = ' ';
++buflen;
}
}
c = buffer[bufpos++];
}
}
}
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