Tracker for potential small additions

[usaoc]

This is an issue specifically for tracking relatively small additions, such as convenience functions, forms, etc. If you feel that a certain nicety is currently missing in Rhombus, please raise it; if you feel like implementing one of them, go ahead! If you have a proposal for more systematic change, though, open a separate issue so that it’s easier to track it.

The current list:

• Reducer
  • [ ] Equivalents for for/first, for/last, etc.
  • [ ] Right fold, i.e., for/foldr
• Sequence
  • [x] Range with a decreasing step (or any step at all), cf. in-range (implemented, as Range.step_by)
    • A way for specifying a decresing step is still missing
• Function
  • [x] Canonical way to do function composition? Say, operators like <</>> (implemented, as compose and compose_values)
  • [x] Pipeline operator (|>)
    • Note: A simple version can be found in rhombus-compat
  • [ ] More pipeline operators
    • [x] &> for chaining maybe results? (implemented, as ?>)
    • [ ] !> for chaining imperative functions?
  • [x] Anonymous function in the style of fancy-app?
    • Note: Previously discussed at #203
• Annotation
  • [x] satisfying, like converting, but for predicate annotations
• Srcloc
  • [ ] Use keyword arguments for constructor
• Exn
  • [ ] Use keyword arguments for constructor