using System;
using System.Text;
using System.CodeDom.Compiler;
using System.Linq;
using System.Reflection;
using Microsoft.VisualBasic;
namespace DrawGraph
{
internal class Function
{
private MethodInfo _evaluateFunction;
private string _expression;
public Function(string f)
{
Expression = f;
}
public Function()
{
}
public string Expression
{
get
{
return _expression;
}
set
{
_expression = ConvertExpression(value);
CreateEvaluator();
}
}
public float Apply(float x)
{
return (float) _evaluateFunction.
Invoke(null,
new object[] {x
}); }
private string ConvertExpression(string expr)
{
StringBuilder converted
= new StringBuilder
(expr.
Replace(" ",
string.
Empty));
for (int i = 0; i < converted.Length; i++)
{
if (char.IsNumber(converted[i]) && i < converted.Length - 1)
{
if (!IsNumberOrOperator(converted[i + 1]))
{
converted.Insert(i + 1, "*");
i++;
}
}
else if (converted[i] == 'x' && i < converted.Length - 1)
{
if (!IsOperator(converted[i + 1]))
{
converted.Insert(i + 1, "*");
i++;
}
}
else if (converted[i] == ')' && i < converted.Length - 1)
{
if (!IsOperator(converted[i + 1]))
{
converted.Insert(i + 1, "*");
i++;
}
}
}
converted = converted.Replace("sin", "Math.Sin")
.Replace("cos", "Math.Cos")
.Replace("tan", "Math.Tan")
.Replace("abs", "Math.Abs")
.Replace("log", "Math.Log")
.Replace("sqrt", "Math.Sqrt");
return converted.ToString();
}
private bool IsNumberOrOperator(char c)
{
const string operators = "+-/*^.,)";
return (char.IsNumber(c) || operators.Contains(c));
}
private bool IsOperator(char c)
{
const string operators = "+-/*^.,)";
return (operators.Contains(c));
}
private void CreateEvaluator()
{
// il codice compilato e` in vb.net poiche` semplifica il parsing dell'espressione
string code = string.Format(
@"Imports System.Collections.Generic
Imports System.Text
Imports System
Imports Microsoft.VisualBasic
Class Evaluator
Const e as Double = math.E
Public Shared Function Evaluate(x As Single) As Single
Return {0}
End Function
End Class", Expression);
var parameters
= new CompilerParameters
(); var provider
= new VBCodeProvider
();
parameters.GenerateExecutable = false;
parameters.TreatWarningsAsErrors = true;
parameters.TempFiles.KeepFiles = false;
parameters.GenerateInMemory = true;
var results = provider.CompileAssemblyFromSource(parameters, code);
if (results.Errors.Count > 0)
throw new Exception
("Espressione non valida!");
var asm = results.CompiledAssembly;
_evaluateFunction = asm.GetType("Evaluator").GetMethod("Evaluate");
}
}
}
