/// <summary>
/// The primary function that make the expression that will be compiled then evaluated.
/// </summary>
/// <param name="tokens"></param>
/// <returns></returns>
public Expression FormTheExpression(Token tokens)
{
Expression quantityExpression = null;
ExprOp eop = null;
ExprOp FirstEop = null;
int ix = 0; //this is the index in the discovered tokens
while (ix < tokens.Count)
{
string q = tokens[ix].TokenValue;
string op = ix + 1 < tokens.Count ? tokens[ix + 1].TokenValue : string.Empty;
if (q == "+" || q == "-")
{
// unary prefix operator.
//consume another token for number
if (q == "+")
{
//q = tokens[ix].TokenValue;
quantityExpression = Expression.Constant(1.0);
}
else
{
quantityExpression = Expression.Constant(-1.0);
}
op = "_h*";
ix--;
goto ExpressionCompleted;
}
if (tokens[ix].TokenClassType == typeof(IfWordToken))
{
// this is an If Word so we need to take all the tokens after it until we find THEN token
// and form expression.
int ifClosingIndex;
Token IfBodyToken = tokens.SubTokens(ix + 1, typeof(ThenWordToken), out ifClosingIndex);
int thenClosingIndex;
Token ThenBodyToken = null;
int elseClosingIndex;
Token ElseBodyToken = null;
ix = ifClosingIndex;
if (ix < tokens.Count)
{
if (tokens[ifClosingIndex].TokenClassType == typeof(ThenWordToken))
{
// True part evaluation
ThenBodyToken = tokens.SubTokens(ix + 1, typeof(ElseWordToken), out thenClosingIndex);
ix = thenClosingIndex;
if (ix < tokens.Count)
{
if (tokens[thenClosingIndex].TokenClassType == typeof(ElseWordToken))
{
// True part evaluation
ElseBodyToken = tokens.SubTokens(ix + 1, typeof(ElseWordToken), out elseClosingIndex);
ix = elseClosingIndex;
}
}
}
}
Expression TestPart = FormTheExpression(IfBodyToken);
Expression TruePart;
Expression FalsePart;
if (ThenBodyToken != null)
TruePart = Expression.Convert(FormTheExpression(ThenBodyToken), typeof(object));
else
TruePart = Expression.Constant(true, typeof(object));
if (ElseBodyToken != null)
FalsePart = Expression.Convert(FormTheExpression(ElseBodyToken), typeof(object));
else
FalsePart = Expression.Constant(false, typeof(object));
quantityExpression = Expression.Condition(TestPart, TruePart, FalsePart);
}
else if (tokens[ix].TokenClassType == typeof(ParenthesisCallToken))
{
quantityExpression = FunctionCallExpression(tokens[ix]);
}
else if (tokens[ix].TokenClassType == typeof(ParenthesisGroupToken))
{
// take the inner tokens and send it to be parsed again.
quantityExpression = FormTheExpression(tokens[ix].RemoveSpaceTokens().TrimTokens(1, 1));
}
else if (tokens[ix].TokenClassType == typeof(SymbolicToken))
{
//
quantityExpression = ExternalFieldHandleExpression(tokens[ix]);
}
else if (tokens[ix].TokenClassType == typeof(NumberToken))
{
//
quantityExpression = Expression.Constant(double.Parse(tokens[ix].TokenValue));
}
else if (tokens[ix].TokenClassType == typeof(WordToken))
{
// we are taking about internal variable storage
quantityExpression = InternalFieldHandleExpression(tokens[ix]);
}
else if (tokens[ix].TokenClassType == typeof(TextToken))
{
quantityExpression = Expression.Constant(tokens[ix].TrimTokens(1, 1).TokenValue);
}
else
{
throw new UnRecognizedException("Token: " + tokens[ix].TokenValue + " was not identified");
}
ExpressionCompleted:
if (eop == null)
{
//firs time creation
FirstEop = new ExprOp();
eop = FirstEop;
}
else
{
//use the next object to be eop.
eop.Next = new ExprOp();
eop = eop.Next;
}
eop.Operation = op;
eop.ValueExpression = quantityExpression;
ix += 2;
}
//then form the calculation expression
return ConstructExpression(FirstEop);
}