数学表达式解释器

示例需求

1. 支持数字、变量、加减乘除运算
2. 支持函数调用（如 max(2,3)）
3. 能够处理嵌套表达式（如 (x + 5) * max(y,10)）

完整代码实现

#include <iostream>
#include <memory>
#include <unordered_map>
#include <vector>
#include <sstream>
#include <cctype>
#include <cmath>

// ====================== 解释器核心组件 ======================
class Context {
   
public:
    std::unordered_map<std::string, double> variables;
    double getVariable(const std::string& name) const {
   
        auto it = variables.find(name);
        if (it == variables.end()) throw std::runtime_error("Undefined variable: " + name);
        return it->second;
    }
};

class Expression {
   
public:
    virtual double interpret(const Context& ctx) const = 0;
    virtual ~Expression() = default;
};

// ====================== 终结符表达式 ======================
class Number : public Expression {
   
    double value;
public:
    Number(double v) : value(v) {
   }
    double interpret(const Context&) const override {
    return value; }
};

class Variable : public Expression {
   
    std::string name;
public:
    Variable(std::string n) : name(std::move(n)) {
   }
    double interpret(const Context& ctx) const override {
   
        return ctx.getVariable(name);
    }
};

// ====================== 非终结符表达式 ======================
class AddExpr : public Expression {
   
    std::unique_ptr<Expression> left, right;
public:
    AddExpr(Expression* l, Expression* r) : left(l), right(r) {
   }
    double interpret(const Context& ctx) const override {
   
        return left->interpret(ctx) + right->interpret(ctx);
    }
};

class MultiplyExpr : public Expression {
   
    std::unique_ptr<Expression> left, right;
public:
    MultiplyExpr(Expression