gistfile1.ml

#light

module SeqMonad = 
  let bindS l f = Seq.concat (Seq.map f l)
  let returnS l = seq { yield l }
  
  type SeqBuilder() =
    member x.Delay(f) = f()
    member x.Bind(l, f) = bindS l f
    member x.Return(l) = returnS l
  let seqM = new SeqBuilder()
  
  let guarded (b:bool) (xs:'a seq) : 'a seq =
    match b with
    | true   -> xs
    | false -> Seq.empty
    
  let res =
    seqM { let! x = seq {1..36}
           let! y = seq {x..36}
           return guarded (x * y = 36) (seq { yield (x, y) })
         }