1 files changed, 67 insertions, 0 deletions
diff --git a/repl.cc b/repl.cc
new file mode 100644
index 0000000..616d0f3
--- /dev/null
+++ b/repl.cc
@@ -0,0 +1,67 @@
+#include <iostream>
+
+#include <stack>
+#include <string>
+#include <algorithm>
+
+#include <cctype>
+#include <cstdlib>
+
+bool is_number(const std::string& token) {
+	return std::all_of(
+		token.begin(),
+		token.end(),
+		[](char c) { return std::isdigit(c); }
+	);
+}
+
+bool is_primitive(const std::string& token) {
+	return token == "+"
+	    || token == "-"
+	    || token == "*"
+	    || token == ".";
+}
+
+void process(std::stack<int>& stack, const std::string& token) {
+	if ( token == "+" ) {
+		const int b = stack.top();
+		stack.pop();
+		const int a = stack.top();
+		stack.pop();
+
+		stack.push(a + b);
+	} else if ( token == "-" ) {
+		const int b = stack.top();
+		stack.pop();
+		const int a = stack.top();
+		stack.pop();
+
+		stack.push(a - b);
+	} else if ( token == "*" ) {
+		const int b = stack.top();
+		stack.pop();
+		const int a = stack.top();
+		stack.pop();
+
+		stack.push(a * b);
+	} else if ( token == "." ) {
+		std::cout << stack.top() << std::endl;
+	}
+}
+
+int main(int, char*[]) {
+	std::stack<int> stack;
+	std::string     token;
+
+	while ( std::cin.good() ) {
+		if ( std::cin >> token ) {
+			if ( is_number(token) ) {
+				stack.push(std::atoi(token.c_str()));
+			} else if ( is_primitive(token) ) {
+				process(stack, token);
+			}
+		}
+	}
+
+	return 0;
+}