example_wrapped.nim

import sequtils
from strutils import join

proc toRna*(dna: string): string =
  result = toSeq(dna)
    .map(c => (
      case c:
        of 'A':
          return "U"
        of 'T':
          return "A"
        of 'C':
          return "G"
        of 'G':
          return "C"
        else:
          raise newException(ValueError, "invalid DNA character detected")
    )).join()