A paper that profoundly influenced my language design: “Programming with Polymorphic Variants” https://caml.inria.fr/pub/papers/garrigue-polymorphic_variants-ml

A paper that profoundly influenced my language design: “Programming with Polymorphic Variants” https://caml.inria.fr/pub/papers/garrigue-polymorphic_variants-ml98.pdf https://caml.inria.fr/pub/papers/garrigue-polymorphic_varian... And the earlier paper “A Polymorphic Type System for Extensible Records and Variants” https://web.cecs.pdx.edu/~mpj/pubs/96-3.pdf https://web.cecs.pdx.edu/~mpj/pubs/96-3.pdf Row types are magically good: they serve either records or variants (aka sum types aka enums) equally well and both polymorphically. They’re duals. Here’s a diagram. Construction Inspection Records {x:1} : {x:Int} r.x — r : {x:Int|r} [closed] [open; note the row variable r] Variants ‘Just 1 : <Just Int|v> case v of ‘Just 0 -> ... [open; note the row var v] v : <Just Int> [closed] Neither have to be declared ahead of time, making them a perfect fit in the balance between play and serious work on my programming language.