Question

I am trying to work with SharePoint 2010 objects with F# (just as experiement).

So I write this code

let getSPDomainUsers (spWeb : SPWeb) =
seq {
  for r in spWeb.RoleAssignments do
    match r.Member with
    | :? SPUser as user ->        
      for b in r.RoleDefinitionBindings do
        if (user.IsDomainGroup) then yield (spWeb.Url.ToLower(), user, b.Name.ToLower())
    | :? SPGroup as group ->
      for u in group.Users do
        for b in r.RoleDefinitionBindings do
          if (u.IsDomainGroup) then yield (spWeb.Url.ToLower(), u, b.Name.ToLower())
    | _ -> ()
} 

However with all these for loops and if conditions my code looks very imperative.

instead of for loop I want to do something like List.map However most of these objects like
RoleDefinitionBindings or RoleAssignments are returning me Collections which are not Lists or Arrays or Sequences so I am forced to write loops.

Can you tell me a way in which I can avoid the loops when the return type is a custom collection object like SPRoleAssignmentCollection and SPRoleDefinitionBindingCollection.

Answer 1

SPRoleDefinitionBindingCollection inherits SPBaseCollection which implements IEnumerable (but not IEnumerable<T>, i.e., seq<'T>). You can use Seq.cast to convert instances of IEnumerable into a seq<'T>.

Once you have a seq<'T> you can use the usual functions in the F# Seq module.

Here’s a cleaned-up version of your code. I don’t have SharePoint so I can’t compile/test it; you may need to explicitly cast the custom collection types to IEnumerable before piping them into Seq.cast.

let userInfo (user : SPUser) =
    user.RoleDefinitionBindings
    |> Seq.cast<SPRoleDefinition>
    |> Seq.choose (fun b ->
        if user.IsDomainGroup then
            Some (spWeb.Url.ToLower(), user, b.Name.ToLower())
        else None)

let getSPDomainUsers (spWeb : SPWeb) =
    spWeb.RoleAssignments
    |> Seq.cast<SPRoleAssignment>
    |> Seq.collect (fun r ->
        match r.Member with
        | :? SPUser as user ->
            userInfo user
        | :? SPGroup as group ->
            Seq.collect userInfo group.Users
        | _ ->
            Seq.empty)