private Expression ParseEquationNoFunctions(string equation)
{
while (equation.IndexOf('(') != -1) //While there are still grouping symbols
{
var subEquation = GetSubExpression(equation.Substring(equation.IndexOf('(') + 1)); //Skip '('
subExpressions.Add(ParseEquationNoFunctions(subEquation));
equation = equation.Replace("(" + subEquation + ")", "{" + (subExpressions.Count - 1).ToString() + "}");
}
CreateExpressions(ref equation, '^');
CreateExpressions(ref equation, '*', '/');
CreateExpressions(ref equation, '-', '+');
using (TypeTextReader reader = new TypeTextReader(new StringReader(equation.Substring(1))))
{
var expressionID = (int)reader.ReadInt64();
return(subExpressions[expressionID]);
}
}
/// <summary>
/// Parses a function as a string into an expression tree.
/// </summary>
/// <param name="function">The string to parse.</param>
/// <returns>The expression tree representing the function.</returns>
public Expression <Func <double, double> > ParseFunctionAsExpressionTree(string function)
{
function = Regex.Replace(function, @"({|\[)", "(");//Replace all non-paren grouping symbols with parens
function = Regex.Replace(function, @"(}|\])", ")");
function = Regex.Replace(function, @"\s", "");
subExpressions.Clear();
subExpressions.Add(x);
subExpressions.Add(Expression.Constant(Math.E));
subExpressions.Add(Expression.Constant(Math.PI));
function = function.Replace(nameof(x), "{0}");
function = function.Replace("e", "{1}");
function = function.Replace("pi", "{2}");
function = Regex.Replace(function, @"(?<number>[0-9]+){", @"${number}*{"); // Handles expressions such as 5x and changes it to 5 * x
if (function[0] == '-')
{
if (function[1] != '{') // If we are not negating a subexpression
{
using (TypeTextReader reader = new TypeTextReader(new StringReader(function.Substring(1))))
{
var val = reader.ReadDouble();
var exprID = subExpressions.Count;
subExpressions.Add(Expression.Constant(-val));
var length = function.Length - reader.BaseReader.ReadToEnd().Length;
function = function.Replace(function.Substring(0, length), "{" + exprID + "}");
}
}
else
{
using (TypeTextReader reader = new TypeTextReader(new StringReader(function.Substring(1))))
{
var subExprId = (int)reader.ReadInt64();
var exprID = subExpressions.Count;
subExpressions.Add(Expression.Negate(subExpressions[subExprId]));
var length = function.Length - reader.BaseReader.ReadToEnd().Length;
function = function.Replace(function.Substring(0, length), "{" + exprID + "}");
}
}
}
var lambda = Expression.Lambda <Func <double, double> >(ParseEquation(function), x);
return(lambda);
}
private void CreateExpressions(ref string equation, params char[] operations)
{
var index = 0;
while ((index = equation.IndexOfAny(operations)) != -1)// While one of the operations can still be performed
{
var previous = equation[index - 1];
Expression left, right;
int startPlaceholder, endPlaceholder;
if (previous == '}')
{
var openingIndex = equation.Substring(0, index).LastIndexOf('{');
var exprID = Int32.Parse(equation.Substring(openingIndex + 1, (index - 1) - (openingIndex + 1)));
left = subExpressions[exprID];
startPlaceholder = openingIndex;
}
else
{
var substr = new string(equation.Substring(0, index).Reverse().ToArray());
var leftVal = Double.NaN;
var leftBuilder = new StringBuilder();
using (StringReader reader = new StringReader(substr))
{
var val = 0;
while ((val = reader.Read()) != -1)
{
var ch = (char)val;
if (Char.IsDigit(ch))
{
leftBuilder.Append(ch);
}
else
{
break;
}
}
leftVal = Double.Parse(new string(leftBuilder.ToString().Reverse().ToArray()));
}
left = Expression.Constant(leftVal);
startPlaceholder = equation.Substring(0, index).LastIndexOf(leftVal.ToString());
}
var next = equation[index + 1];
if (next == '{')
{
var closingIndex = equation.Substring(index).IndexOf('}');
int exprID;
using (TypeTextReader reader = new TypeTextReader(new StringReader(equation.Substring(index + 2))))
{
exprID = (int)reader.ReadInt64();
}
right = subExpressions[exprID];
endPlaceholder = closingIndex + index + 1;
}
else
{
using (TypeTextReader reader = new TypeTextReader(new StringReader(equation.Substring(index + 1))))
{
var exp = reader.ReadDouble();
right = Expression.Constant(exp);
endPlaceholder = equation.Length - reader.BaseReader.ReadToEnd().Length;
}
}
var op = equation[index];
equation = equation.Replace(equation.Substring(startPlaceholder, endPlaceholder - startPlaceholder), "{" + subExpressions.Count.ToString() + "}");
subExpressions.Add(Expression.MakeBinary(ExpTypeFromChar(op), left, right));
}
}
