149 lines
3.6 KiB
Python
149 lines
3.6 KiB
Python
#!/usr/bin/env python3
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import enum
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from collections import namedtuple
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class actions(enum.Enum):
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change, left, right, nothing = range(4)
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State = namedtuple('State', ['action', 'transitions', 'reachable'])
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class SFParseError(Exception): pass
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def parse_smallfuck(s):
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def parse(s, index = 0, in_loop = False):
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parsed = []
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while True:
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assert index <= len(s)
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if index == len(s):
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if in_loop:
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raise SFParseError('Unexpected end of text (expected "]")')
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else:
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break
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c = s[index]
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index += 1
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if c == ']':
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if in_loop:
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break
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else:
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raise SFParseError('Unexpected "]"')
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elif c == '[':
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loop, index = parse(s, index, True)
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parsed.append(loop)
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elif c in ['<', '>', '*']:
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parsed.append(c)
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return parsed, index
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parsed, index = parse(s)
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return parsed
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def turingify(parsed):
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states = []
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def add_state(action, transitions):
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nonlocal states
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assert action in actions
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assert len(transitions) == 2
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index = len(states)
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states.append(State(action, transitions, [False, False]))
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return index
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def worker(parsed, end = None):
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nonlocal states
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while len(parsed) > 0:
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c = parsed[-1]
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parsed = parsed[:-1]
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if type(c) == list:
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loop_test = add_state(actions.nothing, [end, None])
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loop_body = worker(c, loop_test)
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# We want the loop to repeat if the cell is set
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states[loop_test].transitions[1] = loop_body
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end = loop_test
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elif c == '*':
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end = add_state(actions.change, [end, end])
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elif c == '<':
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end = add_state(actions.left, [end, end])
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elif c == '>':
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end = add_state(actions.right, [end, end])
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else:
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assert not "Unreachable"
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return end
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return worker(parsed), states
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def prettyprint_states(states):
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for i in range(len(states)):
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state = states[i]
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action = {actions.change: '* ', actions.left: '< ', actions.right: '> ', actions.nothing: ''}[state.action]
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if state.reachable == [True, True]:
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reachable = '(*)'
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elif state.reachable == [True, False]:
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reachable = '(0)'
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elif state.reachable == [False, True]:
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reachable = '(1)'
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elif state.reachable == [False, False]:
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reachable = '(!)'
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else:
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reachable = ''
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print('%4i%s: %s%s' % (i, reachable, action, state.transitions))
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def reachability(start, states):
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def copy_state(index):
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state = states[index]
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action = state.action
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transitions = state.transitions[:]
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reachable = [False if i is None else i for i in state.reachable]
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return State(action, transitions, reachable)
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# Since we always end up with start at index 0, no need to create processed_start
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processed = [copy_state(start)]
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processed[0].reachable[0] = True
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processed[0].reachable[1] = True
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translations = {start: 0}
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processed_sweep = 0
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while processed_sweep < len(processed):
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for i in range(len(processed[processed_sweep].transitions)):
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index_states = processed[processed_sweep].transitions[i]
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# Nothing to be done if we point to halt state
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if index_states is None:
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continue
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# Copy the state to processed if it isn't already there
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if index_states not in translations:
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index_processed = len(processed)
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processed.append(copy_state(index_states))
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translations[index_states] = index_processed
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# Fix transition to the state
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processed[processed_sweep].transitions[i] = translations[index_states]
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# Mark how we got to the state
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processed[translations[index_states]].reachable[i] = True
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processed_sweep += 1
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return processed
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def main():
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program = input('program: ')
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start_noreachability, states_noreachability = turingify(parse_smallfuck(program))
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processed = reachability(start_noreachability, states_noreachability)
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prettyprint_states(processed)
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if __name__ == '__main__':
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main()
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