def untick

bolt@1.27.0.0 · src/lsp/frame.bend:230

import Base

230# a count one less (zero stays zero)
231def untick(ds: List<&2, Digit>) -> List<&2, Digit>:
232  match ds:
233    case Nil{}:
234      Nil{}
235    case Con{D0{}, t}:
236      D9{} <> untick(t)
237    case Con{D1{}, t}:
238      D0{} <> t
239    case Con{D2{}, t}:
240      D1{} <> t
241    case Con{D3{}, t}:
242      D2{} <> t
243    case Con{D4{}, t}:
244      D3{} <> t
245    case Con{D5{}, t}:
246      D4{} <> t
247    case Con{D6{}, t}:
248      D5{} <> t
249    case Con{D7{}, t}:
250      D6{} <> t
251    case Con{D8{}, t}:
252      D7{} <> t
253    case Con{D9{}, t}:
254      D8{} <> t