expression-trees

问题 Is it possible to implement a ! (not) using expression trees. I'm interested in creating a C# eval class which will parse and evaluate logical expressions which contain true, false, ||, && and !. I know that && and || are currently supported by .NET 4 expression trees, but I was wondering if their is a way to implement summat like !(x && y) || z where z=false, y=true and z=false. Currently I'm using a standard stack based tokenizer, parser, evaluator to evaluate these types of expression but

问题 I want to use an expression in another one: Expression<Func<double, double>> f = x => x * x * 27 + blah ... expression with x; Expression<Func<double, double>> g = y => 3 + 8 * f.Compile()(y) * y * blah... expression with y and f(y); This will not work when sent to LINQ to SQL because f.Compile() is unknown to SQL. How do you evaluate the expression f on the variable y without compiling it, but still using normal syntax to define g ? I don't want to have to define all of g with some

问题 For some fancy reflection stuff, I've got a function of type Func and need to pass it into a function that accepts type Func where T is not known until run time. For example: public bool MyOperation(Func<string,bool> op) { return _myValues.Any(op); } public static bool InvokeOperationMethod(MethodInfo info, object obj,Func<object,bool> opAsObject) { info.Invoke(obj, opAsObject); } The issue is that since I've got a lambda of a weaker type, I can't pass it as an argument of a stronger type. So

问题 Say I have an entity that I want to query with ranking applied: public class Person: Entity { public int Id { get; protected set; } public string Name { get; set; } public DateTime Birthday { get; set; } } In my query I have the following: Expression<Func<Person, object>> orderBy = x => x.Name; var dbContext = new MyDbContext(); var keyword = "term"; var startsWithResults = dbContext.People .Where(x => x.Name.StartsWith(keyword)) .Select(x => new { Rank = 1, Entity = x, }); var

问题 I'm trying to come up with an elegant way to handle some generated polynomials. Here's the situation we'll focus on (exclusively) for this question: order is a parameter in generating an n th order polynomial, where n:=order + 1. i is an integer parameter in the range 0..n The polynomial has zeros at x_j, where j = 1..n and j ≠ i (it should be clear at this point that StackOverflow needs a new feature or it's present and I don't know it) The polynomial evaluates to 1 at x_i. Since this

问题 I'm trying to come up with an elegant way to handle some generated polynomials. Here's the situation we'll focus on (exclusively) for this question: order is a parameter in generating an n th order polynomial, where n:=order + 1. i is an integer parameter in the range 0..n The polynomial has zeros at x_j, where j = 1..n and j ≠ i (it should be clear at this point that StackOverflow needs a new feature or it's present and I don't know it) The polynomial evaluates to 1 at x_i. Since this

问题 I have created a generic search extension method for IQueryable that enables you to search for a single property to see if a search term is contained within it. http://jnye.co/Posts/6/c%23-generic-search-extension-method-for-iqueryable I now want to enable the user to select multiple properties to search within each, matching if any property contains the text. The code: The user enters the following code to perform this search: string searchTerm = "Essex"; context.Clubs.Search(searchTerm,

问题 I am trying to build a lambda expression, containing two assignments (as shown further down), that I can then pass to a Queryable.Select() method. I am trying to pass a string variable into a method and then use that variable to build up the lambda expression so that I can use it in a LINQ Select query. My reasoning behind it is that I have a SQL Server datasource with many column names, I am creating a charting application that will allow the user to select, say by typing in the column name,

问题 Here's what can be done in C# - var two = 2; System.Linq.Expressions.Expression<System.Func<int, int>> expr = x => x * two; expr.Compile().Invoke(4); // returns 8 I wish to do the precise equivalent in F#. Here's what I tried, but did not compile - let two = 2 let expr = (fun x -> x * two) : System.Linq.Expressions.Expression<System.Func<int, int>> expr.Compile().Invoke(4) // desired to return 8 Perhaps predictably, compilation fails on line 2 with the following error - "This function takes

问题 How is it possible to filter data based on some set of filters or expressions that should be used with or operation in where clause? For example, there is a class: class DTOFilter { public string Domain { get; set; } public string Mobile { get; set; } } It is required to filter Users list based on the list of the filters next way: u=> (u.Email.Contains(filters[0].Domain) && u.PhoneNumber.StartsWith(filters[0].Mobile)) || (u.Email.Contains(filters[1].Domain) && u.PhoneNumber.StartsWith(filters