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
  • Equivalent for for/first, for/last, etc.
  • Right fold, i.e., for/foldr
• Sequence
  • Range with a decreasing step (or any step at all), cf. in-range
• Function
  • Canonical way to do function composition? Say, operators like <</>>
  • Pipeline operator (|>)
    • Note: A simple version can be found in rhombus-compat
  • Anonymous function in the style of fancy-app?
    • Note: Previously discussed at `fancy-app` scope #203
• Annotation
  • satisfying, like converting, but for predicate annotations
• Srcloc
  • Use keyword arguments for constructor