36 lines
1.0 KiB
Python
36 lines
1.0 KiB
Python
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#!/usr/bin/env python3
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X_B = {
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('B', 's1'): ('X', 'R', 's2'),
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('B', 's2'): ('B', 'L', 's3'),
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('X', 's3'): ('B', 'R', 's4'),
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('B', 's4'): ('B', 'L', 's1')
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}
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def simulate(instructions):
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# set up initial state
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# note that tape is hard-coded for now, but should be a data structure that
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# can grow in either direction and the state shouldn't be hard-coded. This
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# works for the initial pass at this.
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tape, head, state = ['B', 'B'], 0, 's1'
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# loop: this should be an infinite loop (with a possible halting state in the state table)
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for _ in range(8):
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print(state + ': ' + ''.join(tape))
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print(' ' + ' ' * head + '^')
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# look up instruction
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(tape[head], head_dir, state) = instructions[(tape[head], state)]
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# apply instruction
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head += 1 if head_dir == 'R' else -1
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# sanity checks
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assert(head_dir in ['R', 'L'])
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assert(head >= 0)
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assert(head < len(tape))
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# four lines of actual code that can simulate any CPU
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simulate(X_B)
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