X25519.len: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/src/crypto/curve25519/x25519.bend as X25519
Lines 88-96 of bend-collections@1.0.0.0/src/crypto/curve25519/x25519.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/src/crypto/curve25519/x25519.bend&start_line=88&end_line=96

import Base

# the ladder's bit count, 8 len(k) - 1: 255 for a 32-byte scalar (RFC 7748
# `bits`). Taken from the scalar, it keeps the proof checker from unfolding
# the 255 steps for an unknown scalar.
def len(xs: List<&2, U32>) -> Nat:
  match xs:
    case Nil{}:
      0n
    case Con{x, xt}:
      1n+len(xt)

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=Base/base.bend&name=U32