[daanx]

Looks like a fun project, very nice :-)

For those interested in more of the beautiful theory on extensible row types, this project seems to be based on an earlier paper I wrote on scoped labels: https://www.microsoft.com/en-us/research/wp-content/uploads/...

[jimmyhmiller]

Thanks for the reference. Espresso doesn't support recursive records. Does system in your paper allow for those? Is there anything particularly tricky about supporting them?

[willtim]

Hi, author here, yes your paper was a huge inspiration and I really should add a references section in the readme. The row types in Expresso use very simple lacks constraints, similar to the old Hugs TREX system, and don't permit duplicate/scoped labels. I felt this was also a pretty good sweet spot.

[daanx]

Thanks :-) TREX (by Mark Jones and Benedict Gaster) is great. The beauty is that a lacks constraints can get translated to fields offsets at runtime making it super efficient!

E.g. a type like:

foo :: r/x => { x :: int | r } -> int

foo r = r.x

Gets translated at runtime to a function where the lacks constraint r/x becomes an actual offset parameter.