Implementation Not in .net 4 Expression Trees

Question

Is it possible to implement a! (not) using expression trees. I am interested in creating a C # eval class that will parse and evaluate logical expressions that contain true, false, ||, && as well !. I know that && and || are currently supported by .NET 4 expression trees, but I was wondering if their way of implementing sumat like! (x && y) || z where z = false, y = true and z = false.

I am currently using a standard tokenizer, parser, standard stack based evaluator to evaluate these types of expressions, but happly dump it if a suitable expression tree could be created and executed on the fly.

Answer 1

Usually I find it worthwhile to code a lambda expression that does what I want, and then see what the C # compiler does with it.

So this code:

Expression<Func<bool,bool>> func = x => !x; 

Compiled to:

 ParameterExpression expression2; Expression<Func<bool, bool>> expression = Expression.Lambda<Func<bool, bool>>(Expression.Not( expression2 = Expression.Parameter(typeof(bool), "x")), new ParameterExpression[] { expression2 }); 

(Apologies for formatting - it's hard to figure out what to do about it.)

This is decompiled with Reflector, but with its “optimization” installed on .NET 2.0, to avoid using lambda syntax.

Once you pass the trash, you will see it with Expression.Not . && uses Expression.AndAlso and || uses Expression.OrElse .

Answer 2

It already exists in System.Linq.Expressions . See UnaryExpression . If there is something in the expressions that you don’t like, I would suggest using them. There are also ways to create abstract syntax trees from source code, in particular in Microsoft.Scripting.Ast (found in DLR: Microsoft.Scripting).

Answer 3

This may be useful: http://community.bartdesmet.net/blogs/bart/archive/2009/08/10/expression-trees-take-two-introducing-system-linq-expressions-v4-0.aspx