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using System;
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using System.Collections.Generic;
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using System.Text;
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//Added
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using System.IO;
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public sealed class Lexer
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{
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private readonly IList<object> listLexemes;
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public Lexer(TextReader inputFile)
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{
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listLexemes = new List<object>();
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ReadProgramFile(inputFile);
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}
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public IList<object> GetLexemes
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{
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get
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{
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return listLexemes;
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}
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}
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public enum Tokens
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{
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Add,
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Subtract,
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Multiply,
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Divide,
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Terminator,
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EqualTo,
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LessThan,
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GreaterThan,
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Comma,
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OpenParen,
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CloseParen,
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OpenBrac,
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CloseBrac
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}
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private void ReadProgramFile(System.IO.TextReader programFile)
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{
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while (programFile.Peek() != -1)
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{
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char symbol = (char)programFile.Peek();
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if (char.IsWhiteSpace(symbol))
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{
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// if the symbol is whitespace then move to next symbol
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programFile.Read();
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}
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else if (char.IsLetter(symbol) || symbol == '_')
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{
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//identify the tokens
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StringBuilder token = new StringBuilder();
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while (char.IsLetter(symbol) || symbol == '_')
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{
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token.Append(symbol);
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programFile.Read();
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if (programFile.Peek() == -1)
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{
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break;
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}
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else
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{
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symbol = (char)programFile.Peek();
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}
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}
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listLexemes.Add(token.ToString());
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}
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else if (symbol == '"')
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{
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// string literal
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StringBuilder stringLiteral = new StringBuilder();
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programFile.Read(); // skip the '"'
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if (programFile.Peek() == -1)
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{
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throw new Exception("String literal is not terminated");
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}
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while ((symbol = (char)programFile.Peek()) != '"')
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{
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stringLiteral.Append(symbol);
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programFile.Read();
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if (programFile.Peek() == -1)
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{
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throw new Exception("String literal is not terminated");
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}
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}
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// skip the terminating "
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programFile.Read();
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listLexemes.Add(stringLiteral);
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}
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else if (char.IsDigit(symbol))
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{
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// numeric literal
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StringBuilder numericLiteral = new StringBuilder();
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while (char.IsDigit(symbol))
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{
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numericLiteral.Append(symbol);
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programFile.Read();
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if (programFile.Peek() == -1)
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{
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break;
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}
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else
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{
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symbol = (char)programFile.Peek();
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}
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}
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listLexemes.Add(int.Parse(numericLiteral.ToString()));
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}
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else switch (symbol)
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{
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case '(':
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programFile.Read();
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listLexemes.Add(Tokens.OpenParen);
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break;
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case ')':
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programFile.Read();
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listLexemes.Add(Tokens.CloseParen);
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break;
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case '=':
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programFile.Read();
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listLexemes.Add(Tokens.EqualTo);
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break;
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case ';':
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programFile.Read();
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listLexemes.Add(Tokens.Terminator);
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break;
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case '<':
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programFile.Read();
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listLexemes.Add(Tokens.LessThan);
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break;
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case '>':
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programFile.Read();
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listLexemes.Add(Tokens.GreaterThan);
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break;
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case ',':
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programFile.Read();
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listLexemes.Add(Tokens.Comma);
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break;
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case '/':
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programFile.Read();
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listLexemes.Add(Tokens.Divide);
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break;
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case '*':
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programFile.Read();
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listLexemes.Add(Tokens.Multiply);
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break;
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case '-':
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programFile.Read();
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listLexemes.Add(Tokens.Subtract);
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break;
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case '+':
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programFile.Read();
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listLexemes.Add(Tokens.Add);
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break;
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case '{':
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programFile.Read();
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listLexemes.Add(Tokens.OpenBrac);
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break;
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case '}':
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programFile.Read();
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listLexemes.Add(Tokens.CloseBrac);
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break;
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default:
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ExceptionHandler("unidentified symbol '" + symbol + "'");
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break;
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}
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}
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}
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public void ExceptionHandler(string strException)
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{
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throw new Exception(strException);
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}
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}
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