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uip title description author status type category created
0129
Typed Paths with $coin Extensions
Add %blob and %many to typed paths
~rovnys-ricfer
Draft
Standards Track
Hoon
2024-07-25

Abstract

Hoon's original path data structure has syntax and parsing that allows each element to be a $coin data structure: either a typical string-encoded scalar value, a %many string-encoded list of values or a %blob string-encoded "jammed" (serialized) arbitrary noun. These features are useful for encoding more complex data structures in paths in a standardized and somewhat human-readable manner.

The latest conception of a path in Hoon -- a so-called "typed path", called a $pith in the standard library and introducible using provisional #/foo/bar syntax -- lacks these extra encodings, limiting its expressiveness. This proposal adds the $coin encodings back into typed paths to reclaim the lost expressivity while retaining the performance and legibility improvements of typed paths.

Specification

This is a type definition for a typed path with %many and %blob extensions. Description follows. This does not include parsing or serialization functions.

|%
+$  path  (list zeta)
+$  zeta
  $~  [%n ~]
  $@  @tas
  $%  [%many p=(list zeta)]
      [%blob p=*]
      [%ub @ub]  [%uc @uc]  [%ud @ud]  [%ui @ui]
      [%ux @ux]  [%uv @uv]  [%uw @uw]
      [%sb @sb]  [%sc @sc]  [%sd @sd]  [%si @si]
      [%sx @sx]  [%sv @sv]  [%sw @sw]
      [%da @da]  [%dr @dr]
      [%f ?]     [%n ~]
      [%if @if]  [%is @is]
      [%t @t]    [%ta @ta]  ::  @tas
      [%p @p]    [%q @q]
      [%rs @rs]  [%rd @rd]  [%rh @rh]  [%rq @rq]
  ==
--

A path is a list of zeta elements. Each zeta can either be a @tas, a %many list of elements, a %blob arbitrary noun, or a cell of an atom aura and value, for any aura that is understood natively by the Hoon language.

::  Just like today's typed paths, this typed path
::
#/foo/3/0x4/~2024.7.25
::
::  parses to
::
~[%foo [%ud 3] [%ux 0x4] [%da ~2024.7.25]]
::
::  This typed path takes advantage of the new %blob and %many features:
::
#/baz/~05iggq1/._foo_~~d1_.~-bar~-~-__
::
::  It parses to
::
~[%baz [%blob [33 44]] [%many ~[%foo [%dr ~d1] %many ~[%bar]]]]

Note that %many elements can contain other %many elements recursively, allowing for arbitrary tree shapes of encoded path elements. This example's final %bar is doubly coin-encoded due to being inside two nested %many elements. %blob elements can also be nested inside %many elements.

Backwards Compatibility

I think this new typed path should replace the existing typed path, since it just adds capability -- any typed paths in the existing system, as parsed data structures or strings, should still work.

Once these new typed paths have been demonstrated more thoroughly, the provisional #/ syntax could be replaced by some kind of permanent syntax, possibly replacing the original / path syntax.

Security Considerations

I am not aware of any security considerations to speak of. These paths would be safer if atom sanity was enforced during ;;, as proposed in the Aura Renovation UIP, but that is just as true for existing typed paths.

Copyright

Copyright and related rights waived via CC0.