static IExpression ParseUntil(MathExpressionReader r, Stack<Operator> opStack, Stack<IExpression> output, Token readUntilToken,
int startOpStackSize)
{
do
{
switch (r.CurrentTokenType)
{
case Token.LeftParens:
{
opStack.Push(Ops[OperationType.LeftParens]);
r.ReadToken();
var arg = ParseUntil(r, opStack, output, Token.Coma | Token.RightParens,
opStack.Count);
if (r.CurrentTokenType == Token.Coma)
throw new InvalidDataException("Tuples not supported");
if (r.CurrentTokenType != Token.RightParens)
throw new InvalidDataException("Mismatched parens, missing a closing parens");
output.Push(arg);
while (opStack.TryPeek(out var stackOp) && stackOp.Type != OperationType.LeftParens)
{
opStack.Pop();
PopOpOperandsAndPushNode(stackOp);
}
if (opStack.TryPeek(out var leftParens) && leftParens.Type == OperationType.LeftParens)
opStack.Pop();
else
throw new InvalidDataException("Mismatched parens");
r.ReadToken();
break;
}
/// <summary>
/// Parses a mathematical expression.
/// </summary>
/// <param name="expressionStr">The expression in string to be parsed.</param>
/// <param name="error">The error message if an exception occured.</param>
/// <returns>An IExpression that contains the parsed expression.</returns>
public static IExpression Parse(string expressionStr, out string error)
{
var output = new Stack<IExpression>();
var opStack = new Stack<Operator>();
var r = new MathExpressionReader(expressionStr);
try
{
r.ReadToken();
error = null;
return ParseUntil(r, opStack, output, Token.None, 0);
}
catch (Exception e)
{
error = e.Message;
return null;
}
}
