-- Results: R ok err type for explicit error handling.
-- ~ wraps a value in Ok, ^ wraps in Err.
-- Display: ~value for Ok, ^value for Err.
-- Safe division: Err on divide-by-zero (ends with ~/a b — WrapOk of a binary expr, safe)
div a:n b:n>R n t;=b 0 ^"divide by zero";~/a b
-- Delegate to num builtin: parses text to number or Err (last function — call safe at EOF)
parse tx:t>R n t;num tx
-- run: div 10 2
-- out: ~5
-- run: div 10 0
-- out: ^divide by zero
-- run: parse three
-- out: ^three