public ProgramState Execute(ProgramState state)
{
MyIDictionary <int, MyPair <string, StreamReader> > fileTable = state.GetFileTab();
MyIDictionary <string, int> symTable = state.GetSymTab();
// 1. evaluate var_file_id to a value
int value;
try
{
value = var_file_id.Evaluate(symTable);
}
catch (ExpressionEvaluationException e)
{
throw new MyStatementExecutionException("Cannot read from var " + var_file_id.ToString() + ".");
}
// 2. get the StreamReader object associated in the file table. If there is no entry associated
// with that value in the file table, we stop the execution
StreamReader sr;
try
{
sr = fileTable.Get(value).GetSecond();
}
catch (InvalidKeyMyDictionaryException)
{
throw new MyStatementExecutionException("Error. There is no entry (" + value + ") in the file table.");
}
// 3. Read a line from the file using the ReadLine() method of the StreamReader object.
// If line is null create a zero int value, otherwise translate the string into an int value
int read;
try
{
string line = sr.ReadLine();
read = line.Equals(null) ? 0 : Int32.Parse(line);
}
catch (IOException)
{
throw new MyStatementExecutionException("Error on reading from file.");
}
// 4. Add a new mapping (var_name, int value computed at the previous step) into the sym-table.
// If var_name exists in sym-table, update its associated value instead of adding a new mapping
symTable.Put(var_name, read);
// 5. return
return(null);
}
public ProgramState Execute(ProgramState state)
{
MyIDictionary <string, int> symTab = state.GetSymTab();
try
{
int value = expr.Evaluate(symTab);
symTab.Put(id, value);
}
catch (ExpressionEvaluationException e)
{
Console.WriteLine(e.ToString());
}
return(null);
}
public ProgramState Execute(ProgramState state)
{
MyIDictionary <int, MyPair <string, StreamReader> > fileTable = state.GetFileTab();
MyIDictionary <string, int> symTable = state.GetSymTab();
// 1. check whether the filename is not already in the file table
// If it exists stop the execution with an appropiate error message
foreach (MyPair <string, StreamReader> pair in fileTable.Values())
{
if (pair.GetFirst().Equals(filename))
{
throw new MyStatementExecutionException("File " + filename + " already open.");
}
}
// 2. open the file filename. If the file does not exists or other IO error occurs,
// stop the execution with an appropiate error message
StreamReader sr;
try
{
sr = new StreamReader(filename);
}
catch (FileNotFoundException)
{
throw new MyStatementExecutionException("File " + filename + " does not exist");
}
catch (IOException e)
{
throw new MyStatementExecutionException(e.ToString());
}
// 3. create a new entrance into the file table which maps a new unique integer id
// to the (filename, StreamReader class created before) pair
fileTable.Put(++fd, new MyPair <string, StreamReader>(filename, sr));
// 4. set the var_file_id to that new unique integer key into the sym-table.
symTable.Put(var_file_id, fd);
// 5. return
return(null);
}
