Passing local variables to expression tree as collection list

Question

How can i do pass parameters to an expression tree as collection? For example Expression.Block(params Expression[] expressions) expects parameters as array. So can i create a List collection and pass parameters with this.

for example i translated this code to expression tree

void func(int p1)
{
    int i;
    i = 0;
    for (; i < p1; i++)
    {
        Console.WriteLine("Hello World");
    }
}

to 

 ParameterExpression i = Expression.Parameter(typeof(int), "i");
        ParameterExpression p1 = Expression.Parameter(typeof(int), "p1");
        LabelTarget label = Expression.Label();

        List<Expression> lines = new List<Expression>();
        lines.Add(i);//this is local variable "i" that i declared above
        lines.Add(Expression.Assign(i, Expression.Constant(0)));
        lines.Add(Expression.Loop(
            Expression.Block(
            Expression.IfThenElse(Expression.LessThan(i, p1), Expression.Assign(i, Expression.Add(i, Expression.Constant(1))), Expression.Break(label)),
                Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Hello World"))
            ), label
            ));

        BlockExpression block = Expression.Block(
            lines.ToArray()
            );

        Expression.Lambda<Action<int>>(block, new ParameterExpression[] { p1 }).Compile()(10);

this code compiles but when i run it I get

"UnhandledException:System.InvalidOperationException: variable 'i' of type 'System.Int32' referenced from scope '', but it is not defined"

But i defined "i" with => lines.Add(i); What is wrong here?

How can i add list.Add(A local variable) or is there anyway adding Expression to Block in RunTime like Block.add?

Answer 1

When you declare the block, you need to pass any variables referenced with in the block as the first argument,

BlockExpression block = Expression.Block(
    new ParameterExpression[] { i },
    lines.ToArray()
    );