interpreter.c

来自「Design Pattern C Source Code」· C语言 代码 · 共 183 行

/*
*/
#include "defs.H"
#include <strings.h>
class VariableExp;
class Context;
/*
*/
class BooleanExp {
public:
    BooleanExp();
    virtual ~BooleanExp();
/*
*/
    virtual bool Evaluate(Context&) = 0;
    virtual BooleanExp* Replace(const char*, BooleanExp&) = 0;
    virtual BooleanExp* Copy() const = 0;
};
/*
*/
class Context {
public:
    bool Lookup(const char*) const;
    void Assign(VariableExp*, bool);
};
/*
*/
class VariableExp : public BooleanExp {
public:
    VariableExp(const char*);
    virtual ~VariableExp();
/*
*/
    virtual bool Evaluate(Context&);
    virtual BooleanExp* Replace(const char*, BooleanExp&);
    virtual BooleanExp* Copy() const;
private:
    char* _name;
};
/*
*/
VariableExp::VariableExp (const char* name) {
    _name = strdup(name);
}
/*
*/
bool VariableExp::Evaluate (Context& aContext) {
    return aContext.Lookup(_name);
}
/*
*/
BooleanExp* VariableExp::Copy () const {
    return new VariableExp(_name);
}
/*
*/
BooleanExp* VariableExp::Replace (
    const char* name, BooleanExp& exp
) {
    if (strcmp(name, _name) != 0) {
        return exp.Copy();
    } else {
        return new VariableExp(_name);
   }
}
/*
*/
class AndExp : public BooleanExp {
public:
    AndExp(BooleanExp*, BooleanExp*);
    virtual ~ AndExp();
/*
*/
    virtual bool Evaluate(Context&);
    virtual BooleanExp* Replace(const char*, BooleanExp&);
    virtual BooleanExp* Copy() const;
private:
    BooleanExp* _operand1;
    BooleanExp* _operand2;
};
/*
*/
AndExp::AndExp (BooleanExp* op1, BooleanExp* op2) {
    _operand1 = op1;
    _operand2 = op2;
}
/*
*/
bool AndExp::Evaluate (Context& aContext) {
    return
        _operand1->Evaluate(aContext) &&
        _operand2->Evaluate(aContext);
}
/*
*/
BooleanExp* AndExp::Copy () const {
    return
        new AndExp(_operand1->Copy(), _operand2->Copy());
}
/*
*/
BooleanExp* AndExp::Replace (const char* name, BooleanExp& exp) {
    return
        new AndExp(
            _operand1->Replace(name, exp),
            _operand2->Replace(name, exp)
        );
}
/*
*/
class Constant : public  BooleanExp {
public:
    Constant(int v) { _value = v; };

    virtual bool Evaluate(Context&);
    virtual BooleanExp* Replace(const char*, BooleanExp&);
    virtual BooleanExp* Copy() const;
private:
    int _value;
};

class OrExp : public BooleanExp {
public:
    OrExp(BooleanExp*, BooleanExp*);
    virtual ~ OrExp();

    virtual bool Evaluate(Context&);
    virtual BooleanExp* Replace(const char*, BooleanExp&);
    virtual BooleanExp* Copy() const;
private:
    BooleanExp* _operand1;
    BooleanExp* _operand2;
};

class NotExp : public BooleanExp {
public:
    NotExp(BooleanExp*);
    virtual ~ NotExp();

    virtual bool Evaluate(Context&);
    virtual BooleanExp* Replace(const char*, BooleanExp&);
    virtual BooleanExp* Copy() const;
private:
    BooleanExp* _operand;
};
main () {


/*
*/
BooleanExp* expression;
Context context;

VariableExp* x = new VariableExp("X");
VariableExp* y = new VariableExp("Y");

expression = new OrExp(
    new AndExp(new Constant(true), x),
    new AndExp(y, new NotExp(x))
);
/*
*/
context.Assign(x, false);
context.Assign(y, true);

bool result = expression->Evaluate(context);
/*
*/
BooleanExp* replacement;
VariableExp* z = new VariableExp("Z");

replacement = new NotExp(z);
expression->Replace("Y", *replacement);

context.Assign(z, true);

result = expression ->Evaluate(context);
/*
*/
}
/*
*/