Merge pull request #3 from H5JKey/variable-support

add variables

Author: H5JKey

README.md

@@ -11,7 +11,7 @@ A flexible and extensible C++ library for parsing and evaluating mathematical ex
 - Parentheses and operator precedence
 - Floating-point number support
 - Easy to add new operators, functions and constans
-- Convertation to RPN and it's evaluation
+- Easy to add and use variables
 
 ## Quick Start
 
@@ -28,7 +28,11 @@ int main() {
     parser.registerOperator("max", parser::Operator{
         parser::Operator::Type::FUNCTION, 
         4, false, 2,
-        [](auto args) { return std::max(args[0], args[1]); },
+        [&](auto args) {
+            double left = parser.tokenToDouble(args[0]); // this function convert token to double, according of its type
+            double right = parser.tokenToDouble(args[1]);
+            return Token{MathParser::Token::Type::NUMBER, std::max(left, right)}; 
+        },
         "max"
     });
 
@@ -49,7 +53,10 @@ parser.registerOperator("log", parser::Operator{
     4,         // Precedence
     false,     // Right associativity
     1,         // Single argument
-    [](auto args) { return std::log(args[0]); },
+    [](auto args) {
+          double arg = parser.tokenToDouble(args[0]);
+          return MathParser::Token{MathParser::Token::Type::NUMBER, std::log(arg)};
+    }, // Evaluating function
     "log"      // Function name
 });
 ```

include/mathparser.hpp

@@ -5,10 +5,34 @@
 #include <functional>
 #include <cmath>
 #include <map>
+#include <variant>
+#include <stdexcept>
 
 class MathParser {
 public:
-    using EvaluateFunc = std::function<double(const std::vector<double>&)>;
+    struct Token {
+        enum class Type {
+            OPERATOR,
+            NUMBER,
+            VARIABLE,
+            CONSTANT
+        };
+        Type type;
+        std::variant<double, std::string> value;
+
+        bool operator<(const Token& other) const {
+            if (type != other.type) 
+                return static_cast<int>(type) < static_cast<int>(other.type);
+            
+            switch(type) {
+                case Type::NUMBER:
+                    return std::get<double>(value) < std::get<double>(other.value);
+                default:
+                    return std::get<std::string>(value) < std::get<std::string>(other.value);
+            }
+        }
+    };
+    using EvaluateFunc = std::function<Token(const std::vector<Token>&)>;
     struct Operator {
         enum class Type {
             UNARY,
@@ -23,24 +47,30 @@ class MathParser {
         int operandCount;
         EvaluateFunc evaluate;
         std::string symbol;
-    };   
+    };  
+
 private:
     std::unordered_map<std::string, Operator> operators;
     std::map<std::string, double> constants;
+    std::map<std::string, double> variables;
     void init();
 
     bool isOperator(const std::string& symbol);
     bool isOperator(char symbol);
 
     bool isConstant(const std::string& symbol);
 
+    
+    double evaluateRPN(const std::vector<Token>& RPN);  //evaluate Reverse Polish notation
+    std::vector<Token> toRPN(const std::string& expression);  //make Reverse Polish notation
+
 public:
     MathParser();
     ~MathParser() = default;
 
     void registerOperator(const std::string& symbol, Operator op);
     void registerConstant(const std::string& symbol, double value);
     double evaluate(const std::string& expression);
-    double evaluateRPN(const std::vector<std::string>& RPN);  //evaluate Reverse Polish notation
-    std::vector<std::string> toRPN(const std::string& expression);  //make Reverse Polish notation
+    double tokenToDouble(const Token& token);
+    double getVariableValue(const std::string& varName);
 };

src/main.cpp

@@ -1,4 +1,12 @@
-int main() {
+#include "mathparser.hpp"
+#include <iostream>
 
+int main() {
+    MathParser math;
+    std::cout<<math.evaluate("x=5")<<'\n';
+    std::cout<<math.evaluate("y=7")<<'\n';
+    std::cout<<math.evaluate("x = x+y+1")<<'\n';
+    std::cout<<math.evaluate("variable = x - y")<<'\n';
+    std::cout<<math.getVariableValue("variable");
     return 0;
 }