######################################################################
# busybeaver3.yvtm 
#
# A .yvtm file (yaml virtual turing machine)
# is a representation of a Turing machine.
#
# See:
#   - http://en.wikipedia.org/wiki/Turing_machine
#   - https://en.wikipedia.org/wiki/Busy_beaver
#   - http://www.yaml.org/start.html
#
# There are libraries for reading YAML file for
# lots of coding languages. For python,
# the following code
#
#    >>> import yaml
#    >>> turing = yaml.load(open('busybeaver3.yvtm'))
#
# would give the following python data structure
#
#    turing = {'tape'   : '0',
#              'accept' : [],
#              'reject' : [],
#              'blank'  : '0',
#              'machine': [['one',   '0', 'two',  '1', 'right'],
#                          ['one',   '1', 'HALT', '1', 'right'],
#                          ['two',   '0', 'three','0', 'right'],
#                          ['two',   '1', 'two',  '1', 'right'],
#                          ['three', '0', 'three','1', 'left'],
#                          ['three', '1', 'one',  '1', 'left']]
#             }
#
# Notes :
#   - The tape has blank symbols as far as needed to the left and right.
#   - The leftmost symbol in the "tape" spec is the first read.
#   - The move command is one of (right, left, stay).
#   - The machine should stops after either
#       - moving into any of the accept or reject states
#       - there is no appropriate rule.
#   - The tape (and blank) specification below has quotes 
#     so that it is a string, not a number. (The YAML spec
#     will turn a bare word into a string, but not a bare number.)
#
# Are we having fun yet?
#
#
# Jim Mahoney | Oct 2016 | MIT License
#####################################################################

tape:    "0"
start:   one
blank:   "0"
accept:  []
reject:  []

machine:

#      current  read     next      write   move
#      state    symbol   state     symbol  to
#      -----    ------   --------  -----   -----

   - [ one,     0,       two,      1,      right ]
   - [ one,     1,       HALT,     1,      right ]

   - [ two,     0,       three,    0,      right ]
   - [ two,     1,       two,      1,      right ]

   - [ three,   0,       three,    1,      left  ]
   - [ three,   1,       one,      1,      left  ]