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1 // Var.h
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2
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3 // This is the base class for all variables in rail. The
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4 // acquire/release is for reference counting, which we will use for
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5 // our GC implementation. We can use reference counting here because
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6 // the only primitives are cons (':'), lambda ('&'), and stack
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7 // operations. No modifications of cons cells or closures are allowed.
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8
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9 // The simple tag-based polymorphism here is used because all of the
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10 // actions work only on specific well-defined types. Thus we want
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11 // to bypass the complex multiple-dispatch pattern.
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12
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13 #ifndef VAR_H_RAIL_1
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14 #define VAR_H_RAIL_1
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15
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16 class StringVar;
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17 class ListVar;
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18 class NilVar;
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19 class Closure;
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20
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21 class Var
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22 {
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23 public:
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24 Var() : refCount(0) {}
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25 virtual ~Var() {}
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26
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27 void acquire(void)
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28 {
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29 ++refCount;
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30 }
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31
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32 void release(void)
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33 {
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34 --refCount;
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35 if (refCount <= 0)
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36 {
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37 delete this;
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38 }
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39 }
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40
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41 virtual StringVar * getString(void)=0;
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42 virtual ListVar * getList(void)=0;
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43 virtual NilVar * getNil(void)=0;
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44 virtual Closure * getClosure(void)=0;
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45
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46 virtual std::string toString(void) const=0;
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47 private:
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48 Var(Var const &) {}
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49 Var & operator=(Var const &) { return *this; }
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50 private:
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51 int refCount;
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52 };
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53
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54 #endif
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