######################################################################
# 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 example, this python code
#
#    >>> import yaml
#    >>> turing = yaml.load(open('busybeaver3.yvtm'))
#
# would read this .yvtm file into this 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 stops when either of these two things happens.
#       - It moves into any of the accept or reject states.
#       - There is no appropriate rule to apply.
#   - The symbols, states, and strings in the options and rules may need
#     quotes depending on what characters they contain.
#     For example, if that spec below was
#          tape: 0011
#     then YAML would treat 0011 as a number and ignore the leading zeros.
#     See the YAML spec for the details. If in doubt, use quotes.
#
# See ./yvtm.py for an implementation of a virtual turing machine
# that reads and executes this file.
#
# 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  ]