/// <summary>
/// Parses an atomic production.<para/>
/// An atomic production can be represented as EBNF like:
/// <code><atomic> := [ <literal> ] { <exp> } { <token> { <exp> } }</code><para/>
/// This means that, in an equation such as <c>y=4x√2</c> the three tokens '4', 'x' and '√2' are correctly broken
/// down into three separate multiplications. This is so the algebraic multiplication short-hand of omitting the
/// cross symbol still works. Lastly, this also parses any exponents.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this sub-expression in the order it should be evaluated.</returns>
protected ParseTreeNode ParseAtomic(ParserEnumerator enumerator)
{
ParseTreeNode currentNode = null;
// parse the preceding literal, if there is one
if (enumerator.Check <DigitToken>())
{
currentNode = ParseLiteral(enumerator);
}
if (enumerator.Check <ExpToken>())
{
if (currentNode != null) // we can't exponentiate a non-existent literal
{
currentNode = new BinaryParseTreeNode(
ExpEvaluator,
currentNode,
ParseExponent(enumerator));
}
else
{
throw new ParseException("Expected a valid token before an exponent.", enumerator.Current);
}
}
while (enumerator.Accept <Token>(t => t is IParsable))
{
// parse any other successive tokens
ParseTreeNode currentNodeSubtoken = (enumerator.Current as IParsable).Parse();
if (enumerator.Check <ExpToken>())
{
currentNodeSubtoken = new BinaryParseTreeNode(
ExpEvaluator,
currentNodeSubtoken,
ParseExponent(enumerator));
}
if (currentNode == null)
{
// if the current node is null, create it
currentNode = currentNodeSubtoken;
}
else
{
// otherwise, multiply the existing current node with the new subnode
currentNode = new BinaryParseTreeNode(
MultiplyEvaluator,
currentNode,
currentNodeSubtoken);
}
}
if (currentNode == null)
{
throw new ParseException("Expected a valid token.", enumerator.Current);
}
return(currentNode);
}
/// <summary>
/// Parses this token into a <c>Graphmatic.Expressions.Parsing.ParseTreeToken</c> representing
/// the sequence of calculations needed to evaluate this expression.
/// </summary>
/// <param name="equationParse">Whether to parse as an equation (ie. including the equals sign) or not.</param>
/// <returns>A <c>Graphmatic.Expressions.Parsing.ParseTreeToken</c> representing a syntax tree
/// for this token and any children.</returns>
public ParseTreeNode Parse(bool equationParse)
{
ParserEnumerator enumerator = new ParserEnumerator(this);
ParseTreeNode tree = equationParse ?
ParseEquation(enumerator) :
ParseSummation(enumerator);
return(tree);
}
/// <summary>
/// Parses a series of <c>ExpToken</c>s, and returns the combined power.
/// This function takes advantage of the mathematical identity: <c>(a^b)^c=a^(b*c)</c>. Successive <c>ExpToken</c>s
/// have their powers multiplied together such to return a single power to which to raise the previous expression to.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns the power that the token preceding the parsed <c>ExpToken</c>s should be raised to.</returns>
protected ParseTreeNode ParseExponent(ParserEnumerator enumerator)
{
if (enumerator.Accept <ExpToken>())
{
ParseTreeNode exponentNode = (enumerator.Current as ExpToken).Power.Parse();
while (enumerator.Accept <ExpToken>())
{
exponentNode = new BinaryParseTreeNode(
MultiplyEvaluator,
exponentNode,
(enumerator.Current as ExpToken).Power.Parse());
}
return(exponentNode);
}
else
{
return(null);
}
}
/// <summary>
/// Parses a summation production, handling addition and subtraction.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this sub-expression in the order it should be evaluated.</returns>
protected ParseTreeNode ParseSummation(ParserEnumerator enumerator)
{
ParseTreeNode currentNode = ParseProduction(enumerator);
while (enumerator.Accept <OperationToken>(t =>
t.Operation == OperationToken.OperationType.Add ||
t.Operation == OperationToken.OperationType.Subtract))
{
OperationToken current = enumerator.Current as OperationToken;
if (current.Operation == OperationToken.OperationType.Add)
{
currentNode = new BinaryParseTreeNode(AddEvaluator, currentNode, ParseProduction(enumerator));
}
else if (current.Operation == OperationToken.OperationType.Subtract)
{
currentNode = new BinaryParseTreeNode(SubtractEvaluator, currentNode, ParseProduction(enumerator));
}
}
return(currentNode);
}
/// <summary>
/// Parses a production production (I might have called it that on purpose.)<para/>
/// Basically, this handles multiplication and division.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this sub-expression in the order it should be evaluated.</returns>
protected ParseTreeNode ParseProduction(ParserEnumerator enumerator)
{
ParseTreeNode currentNode = ParseUnary(enumerator);
while (enumerator.Accept <OperationToken>(t =>
t.Operation == OperationToken.OperationType.Multiply ||
t.Operation == OperationToken.OperationType.Divide))
{
OperationToken current = enumerator.Current as OperationToken;
if (current.Operation == OperationToken.OperationType.Multiply)
{
currentNode = new BinaryParseTreeNode(MultiplyEvaluator, currentNode, ParseUnary(enumerator));
}
else if (current.Operation == OperationToken.OperationType.Divide)
{
currentNode = new BinaryParseTreeNode(DivideEvaluator, currentNode, ParseUnary(enumerator));
}
}
return(currentNode);
}
/// <summary>
/// Parses an equation production, handling the equals sign.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this equation.<para/>
/// The equals (=) symbol is essentially equivalent to a subtraction (-) symbol with lower precedence, at least in
/// the context of evaluating the equation.</returns>
protected ParseTreeNode ParseEquation(ParserEnumerator enumerator)
{
ParseTreeNode leftNode = ParseSummation(enumerator), rightNode;
SymbolicToken current = enumerator.Current as SymbolicToken;
if (enumerator.Accept <SymbolicToken>(t => t.Type == SymbolicToken.SymbolicType.Equals))
{
rightNode = ParseSummation(enumerator);
}
else
{
throw new ParseException("Equals sign (=) expected in equation.", enumerator.Current);
}
if (!enumerator.EndReached)
{
throw new ParseException("Unexpected symbol after equation.", enumerator.Current);
}
if (leftNode == null || rightNode == null)
{
throw new ParseException("Equation is incomplete.", enumerator.Current);
}
return(new BinaryParseTreeNode(EqualsEvaluator, leftNode, rightNode));
}
/// <summary>
/// Parses unary operators, such as anything prefixed with + and -.<para/>
/// This correctly swallows any additional operators so as to avoid any huge unnecessary chains of unary negation.
/// This means an expression like <c>y=--++--+--++--++++--x</c> will correctly reduce to <c>y=x</c>.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this sub-expression in the order it should be evaluated.</returns>
protected ParseTreeNode ParseUnary(ParserEnumerator enumerator)
{
bool positive = true;
while (enumerator.Accept <OperationToken>(t =>
t.Operation == OperationToken.OperationType.Add ||
t.Operation == OperationToken.OperationType.Subtract))
{
OperationToken current = enumerator.Current as OperationToken;
if (current.Operation == OperationToken.OperationType.Subtract)
{
positive = !positive;
} // do nothing if the operation token is positive
}
if (positive)
{
return(ParseAtomic(enumerator));
}
else
{
return(new UnaryParseTreeNode(NegationEvaluator, ParseAtomic(enumerator)));
}
}
/// <summary>
/// Parses a literal numeric value. This will correctly accept decimal places and positive/negative exponents.<para/>
/// This works in a bit of a cheaty way, but it saves some code. The entered literal is converted into a string representing
/// the value (turning the <c>*10^</c> operator into the character <c>e</c>) and then parsed using the .NET framework,
/// leaving the conversion from token sequence to double up to Double.Parse.
/// </summary>
/// <param name="enumerator">An enumerator containing the current location in the Expression of the parser.</param>
/// <returns>Returns a parse tree node representing this sub-expression in the order it should be evaluated.</returns>
protected ConstantParseTreeNode ParseLiteral(ParserEnumerator enumerator)
{
StringBuilder builder = new StringBuilder();
double scaleFactor = 1;
if (enumerator.Check <DigitToken>()) // integer component
{
while (enumerator.Accept <DigitToken>())
{
builder.Append((enumerator.Current as DigitToken).Text);
}
}
else
{
throw new ParseException("Literal number must begin with a digit.", enumerator.Current);
}
if (enumerator.Accept <SymbolicToken>(t => t.Type == SymbolicToken.SymbolicType.DecimalPoint)) // decimal place
{
builder.Append('.');
if (enumerator.Check <DigitToken>()) // fractional component
{
while (enumerator.Accept <DigitToken>())
{
builder.Append((enumerator.Current as DigitToken).Text);
}
}
else
{
throw new ParseException("Decimal point in a literal number must be followed by a digit.", enumerator.Current);
}
}
if (enumerator.Accept <SymbolicToken>(t => t.Type == SymbolicToken.SymbolicType.Exp10)) // exponent
{
builder.Append('e');
// optional sign after the '*10^' symbol
if (enumerator.Accept <OperationToken>(t => t.Operation == OperationToken.OperationType.Add))
{
builder.Append('+');
}
if (enumerator.Accept <OperationToken>(t => t.Operation == OperationToken.OperationType.Subtract))
{
builder.Append('-');
}
if (enumerator.Check <DigitToken>())
{
while (enumerator.Accept <DigitToken>())
{
builder.Append((enumerator.Current as DigitToken).Text);
}
}
else
{
throw new ParseException("Exponent symbol in a literal number must be followed by a digit, optionally preceded by a symbol.", enumerator.Current);
}
}
if (enumerator.Accept <SymbolicToken>(t => t.Type == SymbolicToken.SymbolicType.Percent)) // divide by 100 when the percentage sign appears
{
scaleFactor /= 100.0;
}
return(new ConstantParseTreeNode(Double.Parse(builder.ToString()) * scaleFactor));
}
