Roc Zulip Daily Summary — 2026-03-01

  • Realm: https://roc.zulipchat.com
  • Window: 2026-03-01 12:00 AM to 2026-03-02 12:00 AM (America/Los_Angeles)
  • Messages: 5
  • LLM: vertex_open_model model=zai-org/glm-5-maas topics=2 ok=2/2

Top threads

List concatMany and insert

Summary

Jonathan inquires about the existence of a List insert function or a concatMany function to optimize memory allocation, and Luke points him to legacy documentation for the join function while suggesting Dict for insert-heavy use cases.

Key points

  • Jonathan is looking for a way to insert into a List without allocating multiple intermediate arrays.
  • Luke suggests that the old documentation (specifically join) is being ported to the new compiler without major changes.
  • Luke recommends Dict for data structures that require insert-friendly operations, though he notes it may not be fully implemented yet.
  • Jonathan mentions he is attempting to implement a Hash Array Mapped Trie (HAMT) in Roc as a learning exercise.

Open questions

  • Are tree-based data structures (like Scala Vector or Clojure PersistentVector) planned for Roc?

Action items

Key links

Value showing up as opaque type

Summary

Jonathan encountered a compiler bug where a value appeared as an opaque type and caused a segfault when accessing the second payload of a multi-payload tag, which was resolved by refactoring the tag to use a record payload instead.

Key points

  • The issue occurred when pattern matching on a tag with multiple payloads, specifically Just(U64, Str).
  • Printing the matched value v resulted in an opaque type output, and subsequent operations like equality checks caused a crash (status 139).
  • The compiler version used was a debug build (a3741118) on macOS Apple Silicon.
  • The bug was bypassed by changing the tag definition to use a record payload: Just({index: U64, value: v}).

Open questions

  • What is the root cause of the failure to handle multiple payloads in tag types correctly?

Action items