Created
November 23, 2019 15:32
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turing machine simulator
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package main | |
import "fmt" | |
import "strings" | |
const ( | |
Q0 = "q_0" | |
Q1 = "q_1" | |
Q2 = "q_2" | |
Q3 = "q_3" | |
Q4 = "q_4" | |
QReject = `q_{\mathrm{reject}}` | |
QAccept = `q_{\mathrm{accept}}` | |
) | |
const ( | |
A = "a" | |
X = "x" | |
) | |
const Empty = `\sqcup` | |
type Dir string | |
const ( | |
Right Dir = "R" | |
Left Dir = "L" | |
) | |
type Transition struct { | |
headNext, qNext string | |
dir Dir | |
} | |
var ( | |
transitions = map[string]map[string]*Transition{} | |
) | |
func register(qPrev, headPrev, qNext, headNext string, dir Dir) { | |
if _, ok := transitions[qPrev]; !ok { | |
transitions[qPrev] = map[string]*Transition{} | |
} | |
transitions[qPrev][headPrev] = &Transition{ | |
qNext: qNext, | |
headNext: headNext, | |
dir: dir, | |
} | |
} | |
func getTransition(tape []string, idx int, q string) (*Transition, bool) { | |
if _, ok := transitions[q]; !ok { | |
return nil, false | |
} | |
v, ok := transitions[q][tape[idx]] | |
return v, ok | |
} | |
func initTape(arr []string) ([]string, int) { | |
ret := make([]string, 10000) | |
for i := range ret { | |
ret[i] = Empty | |
} | |
copy(ret[5000:], arr) | |
return ret, 5000 | |
} | |
func getStatus(tape []string, idx int, q string) string { | |
tapeIdx := 0 | |
for i := range tape { | |
if tape[i] != Empty { | |
break | |
} | |
tapeIdx = i | |
} | |
tapeEnd := 0 | |
for i := len(tape) - 1; i >= 0; i-- { | |
if tape[i] != Empty { | |
break | |
} | |
tapeEnd = i | |
} | |
return fmt.Sprintf("(%s, {%s}, %d)", q, strings.Join(tape[tapeIdx+1:tapeEnd], "}{"), idx-tapeIdx) | |
} | |
func main() { | |
register(Q0, A, Q1, Empty, Right) | |
register(Q0, Empty, QReject, Empty, Right) | |
register(Q0, X, QReject, X, Right) | |
register(Q1, X, Q1, X, Right) | |
register(Q1, Empty, QAccept, Empty, Right) | |
register(Q1, A, Q2, X, Right) | |
register(Q2, X, Q2, X, Right) | |
register(Q2, A, Q3, A, Right) | |
register(Q2, Empty, Q4, Empty, Left) | |
register(Q3, A, Q2, X, Right) | |
register(Q3, X, Q3, X, Right) | |
register(Q3, Empty, QReject, Empty, Right) | |
register(Q4, A, Q4, A, Left) | |
register(Q4, X, Q4, X, Left) | |
register(Q4, Empty, Q1, Empty, Right) | |
tape, idx := initTape([]string{A, A, A, A}) | |
q := Q0 | |
fmt.Print("&&", getStatus(tape, idx, q)) | |
for tr, ok := getTransition(tape, idx, q); ok; tr, ok = getTransition(tape, idx, q) { | |
tape[idx] = tr.headNext | |
if tr.dir == Right { | |
idx++ | |
} else { | |
idx-- | |
} | |
q = tr.qNext | |
fmt.Println(`\\`) | |
fmt.Print(`&\to& `) | |
fmt.Print(getStatus(tape, idx, q)) | |
} | |
fmt.Println() | |
} |
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