Notes on Implementing Algebraic Subtyping (blog post + language)

Algebraic Subtyping is a type system devised by Stephen Dolan in 2016, in his dissertation. It extends Hindley-Milner with subtyping, in a way that preserves decidability and principality. Over the past few years, I have implemented Algebraic Subtyping in my language Pinafore (omitting record types). Pinafore is, as far as I know, currently the only language to implement this type system besides Dolan’s own MLsub prototype.

See also: Pinafore and Sixteen Unusual Things about Pinafore