Expresso: A simple expressions language with polymorphic extensible row types

Re:Expresso: A simple expressions language with polymorphic ... by willtim on Saturday November 17, 2018 @05:58PM (#18477837)

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.

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Re:Expresso: A simple expressions language with polymorphic ... by daanx on Sunday November 18, 2018 @12:39AM (#18479022)

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.

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