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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 More general machines
Step1:  We've seen finite automata, pushdown automata, and Turing machines, but many other kinds of automata can be created by instantiating a Machine directly.
Step2:  The first argument is required. This machine has four stores, all of type BASE (to be explained below).
The argument state=0 means that store 0 is the state. It's this store that is used to define the start and accept conditions, and this store that is used to define the nodes in a state transition diagram.
The argument input=1 is required and means that store 1 is the input. When the automaton is run, the input string will be placed on this store.
As with other kinds of machines, you can define a start state, transitions, and accept states using set_start_state, add_transition, and add_accept_state.
Step3:  This is something like a 2-stack PDA that recognizes the language ${w###w}$. It works by transferring the first half of the input to the first stack, transferring the first stack to the second stack (reversing it), then checking the second half of the input against it.
This example also demonstrates that we can read three # signs in one transition.
Store types
BASE
Our example above demonstrated the BASE store type. We used a BASE store like a stack, and showed that if the lhs of a transition has more than one symbol, it pops that many symbols. Likewise, if the rhs of a transition has more than one symbol, it pushes that many symbols.
Additionally, a BASE store has a head like a Turing machine; it just happens that we left the head in position 0. If the rhs is ^ v, where v is a string, the head moves to the cell to the left of v; if the rhs is v ^, the head moves to the cell to the right of v.
For more information, see the reference section on Internals.
STREAM
The above example looked different from a standard PDA because the right-hand sides of transitions explicitly popped input symbols as they were read. And it had to explicitly check for a blank (_) indicating the end of the string before accepting. To make the input look more like a finite or pushdown automaton's, use the store type STREAM.
A store of type STREAM (which only really makes sense for the input store) has two properties.
Transitions do not have an entry in their right-hand side for STREAMs; it is implicitly &amp;.
The input must be entirely consumed in order for the machine to accept the input string.
Step4:  This looks just like a pushdown automaton.
TAPE
The caret (^) notation above can be used to move the head as in a Turing machine, but to get more standard notation, use a store of type TAPE. Then the right-hand-side of a transition has two entries for that store, a write and a move (which can be L or R).
Step5:  Low-level interface
Instead of creating an automaton using set_start_state, add_transition, and add_accept_state, you can also directly access the members start_config, transitions, and accept_config.
This interface completely ignores store types. Transitions are created as for BASE stores
Step6:  start_config specifies an initial value for every store (not just the state). The initial value for the input is ignored, as it will be replaced by the input string.
Step7:  accept_configs is a set of configurations, each which specifies a pattern for every store (not just the state).
Step8:  This is how STREAM stores are able to require that the input is fully consumed -- by making the accept configuration for the input store to default to a blank (_).
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Python Code:
from tock import *
Explanation: More general machines
End of explanation
m1 = Machine([BASE, BASE, BASE, BASE], state=0, input=1)
Explanation: We've seen finite automata, pushdown automata, and Turing machines, but many other kinds of automata can be created by instantiating a Machine directly.
End of explanation
m1.set_start_state('q1')
m1.add_transition('q1, &, &, & -> q2, &, $, $')
m1.add_transition('q2, a, &, & -> q2, &, a, &')
m1.add_transition('q2, b, &, & -> q2, &, b, &')
m1.add_transition('q2, # # #, &, & -> q3, &, &, &')
m1.add_transition('q3, &, a, & -> q3, &, &, a')
m1.add_transition('q3, &, b, & -> q3, &, &, b')
m1.add_transition('q3, &, $, & -> q4, &, &, &')
m1.add_transition('q4, a, &, a -> q4, &, &, &')
m1.add_transition('q4, b, &, b -> q4, &, &, &')
m1.add_transition('q4, _, &, $ -> q5, &, &, &')
m1.add_accept_state('q5')
m1
run(m1, 'a a b # # # a a b').shortest_path()
run(m1, 'a a b # # # b a a').has_path()
Explanation: The first argument is required. This machine has four stores, all of type BASE (to be explained below).
The argument state=0 means that store 0 is the state. It's this store that is used to define the start and accept conditions, and this store that is used to define the nodes in a state transition diagram.
The argument input=1 is required and means that store 1 is the input. When the automaton is run, the input string will be placed on this store.
As with other kinds of machines, you can define a start state, transitions, and accept states using set_start_state, add_transition, and add_accept_state.
End of explanation
m2 = Machine([BASE, STREAM, BASE], state=0, input=1)
m2.set_start_state('q1')
m2.add_transition('q1, &, & -> q2, $')
m2.add_transition('q2, a, & -> q2, a')
m2.add_transition('q2, &, & -> q3, &')
m2.add_transition('q3, b, a -> q3, &')
m2.add_transition('q3, &, $ -> q4, &')
m2.add_accept_state('q4')
m2
Explanation: This is something like a 2-stack PDA that recognizes the language ${w###w}$. It works by transferring the first half of the input to the first stack, transferring the first stack to the second stack (reversing it), then checking the second half of the input against it.
This example also demonstrates that we can read three # signs in one transition.
Store types
BASE
Our example above demonstrated the BASE store type. We used a BASE store like a stack, and showed that if the lhs of a transition has more than one symbol, it pops that many symbols. Likewise, if the rhs of a transition has more than one symbol, it pushes that many symbols.
Additionally, a BASE store has a head like a Turing machine; it just happens that we left the head in position 0. If the rhs is ^ v, where v is a string, the head moves to the cell to the left of v; if the rhs is v ^, the head moves to the cell to the right of v.
For more information, see the reference section on Internals.
STREAM
The above example looked different from a standard PDA because the right-hand sides of transitions explicitly popped input symbols as they were read. And it had to explicitly check for a blank (_) indicating the end of the string before accepting. To make the input look more like a finite or pushdown automaton's, use the store type STREAM.
A store of type STREAM (which only really makes sense for the input store) has two properties.
Transitions do not have an entry in their right-hand side for STREAMs; it is implicitly &amp;.
The input must be entirely consumed in order for the machine to accept the input string.
End of explanation
m3 = Machine([BASE, TAPE], state=0, input=1)
m3.set_start_state('q1')
m3.add_transition('q1, a -> q2, b, R')
m3.add_accept_state('q2')
m3
Explanation: This looks just like a pushdown automaton.
TAPE
The caret (^) notation above can be used to move the head as in a Turing machine, but to get more standard notation, use a store of type TAPE. Then the right-hand-side of a transition has two entries for that store, a write and a move (which can be L or R).
End of explanation
for t in m3.transitions: print(t)
m3.transitions.append(machines.Transition('q1, b -> q2, c ^'))
for t in m3.transitions: print(t)
Explanation: Low-level interface
Instead of creating an automaton using set_start_state, add_transition, and add_accept_state, you can also directly access the members start_config, transitions, and accept_config.
This interface completely ignores store types. Transitions are created as for BASE stores:
End of explanation
m3.start_config
m3.start_config = machines.Configuration('q2, &')
m3.start_config
Explanation: start_config specifies an initial value for every store (not just the state). The initial value for the input is ignored, as it will be replaced by the input string.
End of explanation
for c in m3.accept_configs: print(c)
# accept in state q3 if current symbol is a
m3.accept_configs.add(machines.Configuration('q3, a')) 
Explanation: accept_configs is a set of configurations, each which specifies a pattern for every store (not just the state).
End of explanation
for c in m2.accept_configs: print(c)
Explanation: This is how STREAM stores are able to require that the input is fully consumed -- by making the accept configuration for the input store to default to a blank (_).
End of explanation
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