F# XML Type provider and optional types

Question

Using the XML type provider on these two functionally equivalent XML files gives different results with the XML type provider.

XML File 1:

<?xml version="1.0" encoding="utf-8"?>
<params>
  <mode >
     <reg >0</reg>     
  </mode>
  <mode >
     <reg >1.7976931348623157E+308</reg>     
  </mode>
  <mode></mode>
</params>

XML File 2:

<?xml version="1.0" encoding="utf-8"?>
<params>
  <mode>    
  </mode>
  <mode >
    <reg >0</reg>
  </mode>
  <mode >
    <reg >1.7976931348623157E+308</reg>
  </mode>
</params>

Note that the only difference is that the empty "mode" is at the end of one file and the start of the other.

The test F# code looks like this:

type  Test = XmlProvider<""".\test.xml""">
type  Test2 = XmlProvider<""".\test2.xml""">

let xml = Test.GetSample()
let list1 = [for mode in xml.Modes -> mode.Reg]

let xml2 = Test2.GetSample()
let list2 = [for mode in xml2.Modes -> mode.Reg]

list1 has type "Option <float> list" as you would expect. But list2 has type "float list", which is incorrect and causes a runtime exception.

Why does this happen and how can do I avoid this issue?

Answer 1

What version of F# Data are you using? Have you tried with latest 2.x? If it still doesn't work, please submit an issue on https://github.com/fsharp/FSharp.Data/issues

Answer 2

This is fixed in latest F# Data version