lambda expressions in vb.net

Question

I have something that is driving me absolutely crazy...

    Public Function GetAccountGroups() As IList(Of AccountGroup)
        Dim raw_account_groups As IList(Of AccountGroup)
        raw_account_groups = _repository.GetAccountGroups().ToList()
        Dim parents = (From ag In raw_account_groups _
                      Where ag.parent_id = 0 _
                      Select ag).ToList()

        parents(0).sub_account_groups = (From sag In raw_account_groups _
                               Where sag.parent_id = 0 _
                                Select sag).ToList()

        Dim sql_func As Func(Of AccountGroup, List(Of AccountGroup)) = Function(p) _
                                                                      (From sag In raw_account_groups _
                                                                       Where sag.parent_id = p.id _
                                                                       Select sag).ToList()

        parents.ForEach(Function(p) p.sub_account_groups = sql_func(p))

        Return parents
    End Function

The line parents.ForEach(Function(p) p.sub_account_groups = sql_func(p)) has this error...

Operator '=' is not defined for types 'System.Collections.Generic.IList(Of st.data.AccountGroup)' and 'System.Collections.Generic.List(Of st.data.AccountGroup)'.

but I really can't see how it is any different from this code from Rob Connery

public IList<Category> GetCategories() {
    IList<Category> rawCategories = _repository.GetCategories().ToList();                 
    var parents = (from c in rawCategories 
        where c.ParentID == 0
        select c).ToList();
     parents.ForEach(p =>
    {
        p.SubCategories = (from subs in rawCategories
        where subs.ParentID == p.ID
        select subs).ToList();
    });

    return parents; 
}

which compiles perfectly... what am I doing incorrectly?

Answer 1

Lambda's in VB.Net have to return a value, so your equal sign ('=') is being intepreted as a comparison (so that the lambda returns a boolean), rather than an assignment.