Core.opt_at: def of bend-schema-lib@0.4.1.0
Import: import bend-schema-lib@0.4.1.0/core.bend as Core
Lines 1692-1716 of bend-schema-lib@0.4.1.0/core.bend: https://jend.leeeet.dev/read.txt?path=bend-schema-lib@0.4.1.0/core.bend&start_line=1692&end_line=1716

import Base

# An absent value reaches the top of what enc writes for s: s is an SOptional,
# or it hands the value it was given straight to a schema that is (a rule, a
# strict object, a bound, or the tail of a variant or tagged chain -- and an
# SOpt, whose Some case passes the value through). Everything else wraps what
# it writes in a constructor of its own, so an absent value cannot surface.
def opt_at(s: Schema) -> Bool:
  match s:
    case SOptional{i}:
      True{}
    case SOpt{i}:
      opt_at(i)
    case SRule{s2, tag}:
      opt_at(s2)
    case SStrict{s2}:
      opt_at(s2)
    case SStrLen{lo, hi, s2}:
      opt_at(s2)
    case SListLen{lo, hi, s2}:
      opt_at(s2)
    case STagged{k, n, cs, rest}:
      opt_at(rest)
    case SVariant{n, vs, rest}:
      opt_at(rest)
    case _:
      False{}

Uses (2):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=bend-schema-lib@0.4.1.0/core.bend&name=Schema