Implement primitives as lambda expressions in an unordered set

1 files changed, 66 insertions, 49 deletions

diff --git a/repl.cc b/repl.cc
index a44a733..31d8b07 100644
--- a/repl.cc
+++ b/repl.cc
@@ -4,6 +4,9 @@
 #include <string>
 #include <algorithm>
 
+#include <unordered_map>
+#include <functional>
+
 #include <cctype>
 #include <cstdlib>
 
@@ -15,65 +18,79 @@ bool is_number(const std::string& token) {
 	);
 }
 
-bool is_primitive(const std::string& token) {
-	return token == "+"
-	    || token == "-"
-	    || token == "*"
-	    || token == "."
-	    || token == "swp"
-	    || token == "dup"
-	    || token == "del";
-}
-
-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();
+int main(int, char*[]) {
+	std::stack<int> stack;
+	std::string     token;
 
-		stack.push(a + b);
-	} else if ( token == "-" ) {
-		const int b = stack.top();
-		stack.pop();
-		const int a = stack.top();
-		stack.pop();
+	std::unordered_map<std::string, std::function<void(void)>> builtin{
+		{
+			"+", [&stack]() {
+				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);
+			}
+		},
+		{
+			"-", [&stack]() {
+				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;
-	} else if ( token == "swp" ) {
-		const int b = stack.top();
-		stack.pop();
-		const int a = stack.top();
-		stack.pop();
+				stack.push(a - b);
+			}
+		},
+		{
+			"*", [&stack]() {
+				const int b = stack.top();
+				stack.pop();
+				const int a = stack.top();
+				stack.pop();
 
-		stack.push(b);
-		stack.push(a);
-	} else if ( token == "dup" ) {
-		stack.push(stack.top());
-	} else if ( token == "del" ) {
-		stack.pop();
-	}
-}
+				stack.push(a * b);
+			}
+		},
+		{
+			".", [&stack]() {
+				std::cout << stack.top() << std::endl;
+			}
+		},
+		{
+			"swp", [&stack]() {
+				const int b = stack.top();
+				stack.pop();
+				const int a = stack.top();
+				stack.pop();
 
-int main(int, char*[]) {
-	std::stack<int> stack;
-	std::string     token;
+				stack.push(b);
+				stack.push(a);
+			}
+		},
+		{
+			"dup", [&stack]() {
+				stack.push(stack.top());
+			}
+		},
+		{
+			"del", [&stack]() {
+				stack.pop();
+			}
+		}
+	};
 
 	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);
+			} else {
+				const auto& impl = builtin.find(token);
+
+				if ( impl != builtin.end() ) {
+					impl->second();
+				}
 			}
 		}
 	}