# Domain Driven Type Narrowing

**URL:** <https://discourse.elm-lang.org/t/domain-driven-type-narrowing/7753>\
**Category:** Learn\
**Created:** [September 13, 2021, 2:19am UTC](https://discourse.elm-lang.org/t/domain-driven-type-narrowing/7753 "2021-09-13T02:19:34Z")\
**Posts on this page:** 1\
**Showing post:** 38

<div class="post-metadata">

**Author:** ![nickwalt](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.elm-lang.org/nickwalt/32/1283_2.png) [@nickwalt](https://discourse.elm-lang.org/u/nickwalt)\
**Post date:** [October 1, 2021, 11:52am UTC](https://discourse.elm-lang.org/t/domain-driven-type-narrowing/7753/38 "2021-10-01T11:52:16Z")

</div>

> [@rupert](#):
>
> Been a while since I read the Scott Wlaschin Domain Modelling in F# book - does he describe the phantom builder pattern with extensible record types there? Or some equivalent in F#.

Good question - I cannot tell. I’ll have to learn all about the builder pattern in Elm before I can answer that question.

---

_[View the full topic](https://discourse.elm-lang.org/t/domain-driven-type-narrowing/7753)._