HIW 2021 - A new interface for GHC typechecker plugins and type-family rewriting

Whole-channel inclusion: ACM SIGPLAN is an honest teaching channel (title sample + 3 transcripts read: All three samples lack transcripts, so the channel verdict relies on the prior title-sample assessment indicating near-entirely academic conference talks and tutorials.); this title passed a strict title check (sonnet) after a labelling pass.