anchor.diff:  let ``tx monad rollback and zero`` () = 
       let c = withMemDb()
       let tran() = tx {
  -        do! Tx.execNonQueryi "insert into person (id,name) values (@id, @name)" [P("@id",3);P("@name", "juan")]
  +        do! txInsert 3
           if 1 = 1
               then do! Tx.rollback 4
           return 0
  
positive.code:     let c = withMemDb()
      let tran() = tx {
          for i in 1..50 do
              do! Tx.execNonQueryi "insert into person (id,name) values (@id, @name)" [P("@id",1);P("@name", "juan")]
      }
      let result = tran() c
      match result with
  
negative.code: let ``tx monad composable`` () =
      let c = withMemDb()
      let tran1() = tx {
          do! txInsert 3
      }
      let tran() = tx {
          do! tran1()
          do! txInsert 4
      }
      let result = tran() c
      match result with
  