Tree.groups: def of bolt@1.27.0.0
Import: import bolt@1.27.0.0/src/syntax/tree.bend as Tree
Lines 210-216 of bolt@1.27.0.0/src/syntax/tree.bend: https://jend.leeeet.dev/read.txt?path=bolt@1.27.0.0/src/syntax/tree.bend&start_line=210&end_line=216

import Base

# how many groups sit open on top of the stack
def groups(stack: List<&2, Frame>) -> Nat:
  match stack:
    case Con{FGroup{open, kids}, rest}:
      Succ{groups(rest)}
    case other:
      0n

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=bolt@1.27.0.0/src/syntax/tree.bend&name=Frame