You can build an expression tree to perform a while loop by using Expression.Loop method. For example, you have the following code.
var result = 1;
while (n > 1)
{
result = result * n;
n--;
}
Console.WriteLine(result);
Here is the code that is required to build the same functionality using expression tree.
var nArgument = Expression.Parameter(typeof(int), "n");
var result = Expression.Variable(typeof(int), "result");
// Creating a label that represents the return value
LabelTarget label = Expression.Label(typeof(int));
var initializeResult = Expression.Assign(result, Expression.Constant(1));
// This is the inner block that performs the multiplication,
// and decrements the value of 'n'
var ifTrueBlock = Expression.Block(
Expression.Assign(result,
Expression.Multiply(result, nArgument)),
Expression.PostDecrementAssign(nArgument)
);
var ifThenElseExpr = Expression.IfThenElse(
Expression.GreaterThan(nArgument, Expression.Constant(1)),
ifTrueBlock,
Expression.Break(label, result)
);
// Creating a method body.
BlockExpression body = Expression.Block(
new[] { result },
initializeResult,
Expression.Loop(ifThenElseExpr, label)
);
// Compile and run an expression tree.
var factorial = Expression.Lambda<Func<int, int>>(body, nArgument).Compile();
Console.WriteLine(factorial(6));