public Func <int, int> Factorial()
{
// Creating a parameter expression.
var value = Expression.Parameter(typeof(int), "value");
// Creating an expression to hold a local variable.
var result = Expression.Variable(typeof(int), "result");
// Creating a label to jump to from a loop.
var label = Expression.Label(typeof(int));
// Creating a method body.
var block = Expression.Block(
new[] { result },
Expression.Assign(result, Expression.Constant(1)),
Expression.Loop(
Expression.IfThenElse(
Expression.GreaterThan(value, Expression.Constant(1)),
Expression.MultiplyAssign(result,
Expression.PostDecrementAssign(value)),
Expression.Break(label, result)
),
label
)
);
return(Expression.Lambda <Func <int, int> >(block, value).Compile());
}