Compile and run dynamic code, without generating EXE?

Question

I was wondering if it was possible to compile, and run stored code, without generating an exe or any type of other files, basically run the file from memory.

Basical

Answer 1

In Mono you use CSharp.Evaluator. It works truly in memory v. some of the other solutions mentioned that write out and read back in a file under the hood.

Answer 2

Here is an example of how to use System.Linq.Expressions to add to Tim's answer. Obviously it isn't the prettiest code but having it in this nice tree-like form makes development so easy.

private  Expression<IsWordChar> CreateIsWordCharExpression()
{
    var e = Expression.Parameter(typeof(int), "e");
    var c = Expression.Variable(typeof(char), "c");
    var returnLabel = Expression.Label(Expression.Label(typeof(bool)), _falseConstant);
    var lambda = Expression.Lambda<IsWordChar>(
        Expression.Block(
            new[] { c },
            Expression.IfThen(
                Expression.OrElse(
                    Expression.Equal(e, Expression.Constant(-1)),
                    Expression.Equal(e, _inputLengthVar)
                ),
                Expression.Return(returnLabel.Target, _falseConstant)
            ),
            Expression.Assign(c, Expression.MakeIndex(_str, _stringCharsPropertyInfo, new[] { e })),
            Expression.IfThenElse(
                Expression.OrElse(
                    Expression.OrElse(
                        Expression.OrElse(
                            Expression.AndAlso(
                                Expression.GreaterThanOrEqual(c, Expression.Constant('a')),
                                Expression.LessThanOrEqual(c, Expression.Constant('z'))
                            ),
                            Expression.AndAlso(
                                Expression.GreaterThanOrEqual(c, Expression.Constant('A')),
                                Expression.LessThanOrEqual(c, Expression.Constant('Z'))
                            )
                        ),
                        Expression.AndAlso(
                            Expression.GreaterThanOrEqual(c, Expression.Constant('0')),
                            Expression.LessThanOrEqual(c, Expression.Constant('1'))
                        )
                    ),
                    Expression.Equal(c, Expression.Constant('_'))
                ),
                Expression.Return(returnLabel.Target, _trueConstant),
                Expression.Return(returnLabel.Target, _falseConstant)
            ),
            returnLabel
        ),
        "IsWordChar",
        new[] { e }
    );
    return lambda;
}