public static Expression <Func <T, bool> > ToExpression <T>(this AxiomFilter filter)
{
var axDict = GetAxiomExpressionDictionary <T>(filter);
filter.Format = filter.Format.Replace(AND_ALSO, AND).Replace(OR_ELSE, OR);
var junctionDict = new Dictionary <string, Func <Expression <Func <T, bool> >, Expression <Func <T, bool> >, Expression <Func <T, bool> > > >()
{
{ AND, TypeExtensions.AndAlso },
{ OR, TypeExtensions.OrElse }
};
Func <string, bool> IsBinOperator = (string s) =>
{
return(s == AND || s == OR);
};
Func <string, bool> IsUnaryOperator = (string s) =>
{
return(s == NOT);
};
Func <object, Expression <Func <T, bool> > > GetAxiomFunc = (object o) =>
{
if (!(o is Token))
{
return(o as Expression <Func <T, bool> >);
}
return(axDict[((Token)o).Value]);
};
using (var reader = new StringReader(filter.Format))
{
var parser = new Parser();
var tokens = parser.Tokenize(reader).ToList();
var rpn = parser.ShuntingYard(tokens).ToList();
var processStack = new Stack <object>();
var i = 0;
do
{
var t = rpn[i];
if (IsBinOperator(t.Value))
{
processStack.Push(
junctionDict[t.Value](
GetAxiomFunc(processStack.Pop()),
GetAxiomFunc(processStack.Pop())
)
);
}
else if (IsUnaryOperator(t.Value))
{
processStack.Push(
TypeExtensions.Not(
GetAxiomFunc(processStack.Pop())
)
);
}
else
{
processStack.Push(t);
}
i++;
}while (i < rpn.Count);
var exp = processStack.Pop() as Expression <Func <T, bool> >;
return((exp.CanReduce)
? exp.Reduce() as Expression <Func <T, bool> >
: exp);
}
}
private static Dictionary <string, Expression <Func <T, bool> > > GetAxiomExpressionDictionary <T>(AxiomFilter filter)
{
var type = typeof(T);
var axiomDict = new Dictionary <string, Expression <Func <T, bool> > >();
var paramExpression = Expression.Parameter(type, "🖕🏽");
foreach (var a in filter.Axioms)
{
var conditionalExpression = a.ToExpression <T>(paramExpression);
axiomDict.Add($"{{{a.Key}}}", conditionalExpression);
}
return(axiomDict);
}