Eval: Add special form "do"

src/eval.cpp

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: MIT
  */
 
-#include <iterator> // sd::advance, std::next
+#include <iterator> // sd::advance, std::next, std::prev
 #include <list>
 #include <memory> // std::static_pointer_cast
 #include <span>   // std::span
@@ -57,6 +57,9 @@ ASTNodePtr Eval::evalImpl(ASTNodePtr ast, EnvironmentPtr env)
 		if (symbol == "let*") {
 			return evalLet(nodes, env);
 		}
+		if (symbol == "do") {
+			return evalDo(nodes, env);
+		}
 	}
 
 	// Function call
@@ -200,6 +203,22 @@ ASTNodePtr Eval::evalLet(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
 	return evalImpl(second_argument, let_env);
 }
 
+ASTNodePtr Eval::evalDo(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
+{
+	if (nodes.size() == 0) {
+		Error::the().addError(format("wrong number of arguments: do, {}", nodes.size()));
+		return nullptr;
+	}
+
+	// Evaluate all nodes except the last
+	for (auto it = nodes.begin(); it != std::prev(nodes.end(), 1); ++it) {
+		evalImpl(*it, env);
+	}
+
+	// Eval and return last node
+	return evalImpl(nodes.back(), env);
+}
+
 ASTNodePtr Eval::apply(std::shared_ptr<List> evaluated_list)
 {
 	if (evaluated_list == nullptr) {

src/eval.h

@@ -27,6 +27,7 @@ private:
 	ASTNodePtr evalAst(ASTNodePtr ast, EnvironmentPtr env);
 	ASTNodePtr evalDef(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env);
 	ASTNodePtr evalLet(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env);
+	ASTNodePtr evalDo(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env);
 	ASTNodePtr apply(std::shared_ptr<List> evaluated_list);
 
 	ASTNodePtr m_ast;