module Standard {
    module Algorithms {
        Filter(this, comp) {
            comptype := Expression(Utility.Forward(comp)).Type;
            thistype := Expression(Utility.Forward(this)).Type;
            if ((Utility.IsMovable(comptype) && comptype.IsRRef()) || Utility.IsCopyable(comptype)
             && (Utility.IsMovable(thistype) && thistype.IsRRef()) || Utility.IsCopyable(thistype)) {
                it_type := type {
                };
                resulttype := type {
                    func := Utility.Forward(comp);
                    src := Utility.Forward(this);
                };
                return resulttype();
            }
            // Not suitable for lazy evalutation, eagerly evaluate.
            result := Containers.Vector(Compiler.Expression(*this.Begin).Type)();
            while(this) {
                x := *this.Begin;
                if (comp(x)) result.Insert(result.Back(), x);
                ++this.Begin;
            }
            return result;
        }
    }
}