A TM to duplicate a string

tm-dup.yaml

name: divisible by 3
source code: |-
  # A TM to duplicate a string.
  # (That is, compute f(w) = ww.)
  #
  # @author: ibarland@radford.edu
  # run this at: https://turingmachine.io/?import-gist=7732e683354339c9993fb0fe5390af90
  # assignment: https://www.radford.edu/itec420/2020fall-ibarland/Homeworks/hw06.html
  # 
  input: 'abbab'
  blank: '_'
  start state: copyChar

  table:
    copyChar:
      a: {write: A, R: carryA}
      b: {write: B, R: carryB}
      
    carryA:
      [a,b,A,B]: R
      _: {write: A, L: moveLPastCopied }
      
    carryB:
      [a,b,A,B]: R
      _: {write: B, L: moveLPastCopied }
      
    moveLPastCopied:
      [A,B]: L
      [a,b]: {L: moveLPastUncopied }
      _:  {R: fixup}   # we've copied everything!
      
    moveLPastUncopied:
      [a,b]: L
      [A,B]: {R: copyChar }

    fixup:
      A: {write: a, R}
      B: {write: b, R}
      _: {L: returnHome}

    returnHome:
      [a,b]: L
      _: {R: halt}
      
    halt:
positions:
  copyChar: {x: 219.53, y: 124.87}
  carryA: {x: 566.33, y: 77.01}
  carryB: {x: 476.55, y: 148}
  moveLPastCopied: {x: 454.11, y: 297.98}
  moveLPastUncopied: {x: 278.68, y: 298.78}
  fixup: {x: 512.65, y: 342.47}
  returnHome: {x: 563.37, y: 386.52}
  halt: {x: 614.27, y: 428.81}