irc: improve multi-line strings; complete list concat and dynamic attrs

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I64e53c68d90b62f3ca306865ceda32af6a6a6964

src/irc/evaluator.cpp

@@ -5,9 +5,7 @@
 #include "evaluator.h"
 #include "nix/expr/eval.hh"
 #include "nix/expr/value.hh"
-#include "nix/util/error.hh"
-
-#include <stdexcept>
+#include "nix/util/url.hh"
 #include <unordered_map>
 
 namespace nix_irc {
@@ -66,11 +64,7 @@ struct Evaluator::Impl {
 
   explicit Impl(EvalState& s) : state(s) {}
 
-  ~Impl() {
-    for (auto& env : environments) {
-      delete env.release();
-    }
-  }
+  // Destructor not needed - unique_ptr handles cleanup automatically
 
   IREnvironment* make_env(IREnvironment* parent = nullptr) {
     auto env = new IREnvironment(parent);
@@ -108,14 +102,42 @@ struct Evaluator::Impl {
 
     if (auto* n = node->get_if<ConstIntNode>()) {
       v.mkInt(n->value);
+    } else if (auto* n = node->get_if<ConstFloatNode>()) {
+      v.mkFloat(n->value);
     } else if (auto* n = node->get_if<ConstStringNode>()) {
       v.mkString(n->value);
     } else if (auto* n = node->get_if<ConstPathNode>()) {
-      v.mkPath(state.rootPath(CanonPath(n->value)));
+      std::string path = n->value;
+      // Expand ~/ to home directory
+      if (path.size() >= 2 && path[0] == '~' && path[1] == '/') {
+        const char* home = getenv("HOME");
+        if (home) {
+          path = std::string(home) + path.substr(1);
+        }
+      }
+      v.mkPath(state.rootPath(CanonPath(path)));
     } else if (auto* n = node->get_if<ConstBoolNode>()) {
       v.mkBool(n->value);
-    } else if (auto* n = node->get_if<ConstNullNode>()) {  // NOLINT(bugprone-branch-clone)
+    } else if (auto* n = node->get_if<ConstNullNode>()) { // NOLINT(bugprone-branch-clone)
       v.mkNull();
+    } else if (auto* n = node->get_if<ConstURINode>()) {
+      // Parse and validate URI, then create string with URI context
+      auto parsed = parseURL(n->value, true);
+      // Store URI with context - use simple mkString with context
+      v.mkString(parsed.to_string(), nix::NixStringContext{});
+    } else if (auto* n = node->get_if<ConstLookupPathNode>()) {
+      // Lookup path like <nixpkgs>; resolve via Nix search path
+      // We can use EvalState's searchPath to resolve
+      auto path = state.findFile(n->value);
+      v.mkPath(path);
+    } else if (auto* n = node->get_if<ListNode>()) {
+      // Evaluate list - allocate and populate
+      auto builder = state.buildList(n->elements.size());
+      for (size_t i = 0; i < n->elements.size(); i++) {
+        builder.elems[i] = state.allocValue();
+        eval_node(n->elements[i], *builder.elems[i], env);
+      }
+      v.mkList(builder);
     } else if (auto* n = node->get_if<VarNode>()) {
       Value* bound = env ? env->lookup(n->index) : nullptr;
       if (!bound && env && n->name.has_value()) {
@@ -216,6 +238,22 @@ struct Evaluator::Impl {
             v.mkInt((left->integer() + right->integer()).valueWrapping());
           } else if (left->type() == nString && right->type() == nString) {
             v.mkString(std::string(left->c_str()) + std::string(right->c_str()));
+          } else if (left->type() == nPath && right->type() == nString) {
+            // Path + string = path
+            std::string leftPath = std::string(left->path().path.abs());
+            std::string result = leftPath + std::string(right->c_str());
+            v.mkPath(state.rootPath(CanonPath(result)));
+          } else if (left->type() == nString && right->type() == nPath) {
+            // String + path = path
+            std::string rightPath = std::string(right->path().path.abs());
+            std::string result = std::string(left->c_str()) + rightPath;
+            v.mkPath(state.rootPath(CanonPath(result)));
+          } else if (left->type() == nPath && right->type() == nPath) {
+            // Path + path = path
+            std::string leftPath = std::string(left->path().path.abs());
+            std::string rightPath = std::string(right->path().path.abs());
+            std::string result = leftPath + rightPath;
+            v.mkPath(state.rootPath(CanonPath(result)));
           } else {
             state.error<EvalError>("type error in addition").debugThrow();
           }
@@ -286,10 +324,60 @@ struct Evaluator::Impl {
             state.error<EvalError>("type error in comparison").debugThrow();
           }
           break;
-        case BinaryOp::CONCAT:
-          // ++ is list concatenation in Nix; string concat uses ADD (+)
-          state.error<EvalError>("list concatenation not yet implemented").debugThrow();
+        case BinaryOp::CONCAT: {
+          // List concatenation: left ++ right
+          if (left->type() != nList || right->type() != nList) {
+            state.error<EvalError>("list concatenation requires two lists").debugThrow();
+          }
+
+          size_t left_size = left->listSize();
+          size_t right_size = right->listSize();
+          size_t total_size = left_size + right_size;
+
+          auto builder = state.buildList(total_size);
+          auto left_view = left->listView();
+          auto right_view = right->listView();
+
+          // Copy elements from left list
+          size_t idx = 0;
+          for (auto elem : left_view) {
+            builder.elems[idx++] = elem;
+          }
+
+          // Copy elements from right list
+          for (auto elem : right_view) {
+            builder.elems[idx++] = elem;
+          }
+
+          v.mkList(builder);
           break;
+        }
+        case BinaryOp::MERGE: {
+          // // is attrset merge - right overrides left
+          if (left->type() != nAttrs || right->type() != nAttrs) {
+            state.error<EvalError>("attrset merge requires two attrsets").debugThrow();
+          }
+
+          // Build a map of right attrs first (these have priority)
+          std::unordered_map<Symbol, Value*> right_attrs;
+          for (auto& attr : *right->attrs()) {
+            right_attrs[attr.name] = attr.value;
+          }
+
+          // Copy right attrs to result
+          auto builder = state.buildBindings(left->attrs()->size() + right->attrs()->size());
+          for (auto& attr : *right->attrs()) {
+            builder.insert(attr.name, attr.value);
+          }
+          // Add left attrs that don't exist in right
+          for (auto& attr : *left->attrs()) {
+            if (right_attrs.find(attr.name) == right_attrs.end()) {
+              builder.insert(attr.name, attr.value);
+            }
+          }
+          v.mkAttrs(builder.finish());
+          break;
+        }
         default:
           state.error<EvalError>("unknown binary operator").debugThrow();
         }
@@ -335,17 +423,16 @@ struct Evaluator::Impl {
     } else if (auto* n = node->get_if<LetNode>()) {
       auto let_env = make_env(env);
       for (const auto& [name, expr] : n->bindings) {
-        Value* val = make_thunk(expr, env);
+        // Create thunks in let_env so bindings can reference each other
+        Value* val = make_thunk(expr, let_env);
         let_env->bind(val);
       }
       eval_node(n->body, v, let_env);
     } else if (auto* n = node->get_if<LetRecNode>()) {
       auto letrec_env = make_env(env);
-      std::vector<Value*> thunk_vals;
 
       for (const auto& [name, expr] : n->bindings) {
         Value* val = make_thunk(expr, letrec_env);
-        thunk_vals.push_back(val);
         letrec_env->bind(val);
       }
 
@@ -355,21 +442,36 @@ struct Evaluator::Impl {
 
       IREnvironment* attr_env = env;
       if (n->recursive) {
+        // For recursive attrsets, create environment where all bindings can
+        // see each other
         attr_env = make_env(env);
-        for (const auto& [key, val] : n->attrs) {
-          Value* thunk = make_thunk(val, attr_env);
-          attr_env->bind(thunk);
+        for (const auto& binding : n->attrs) {
+          if (!binding.is_dynamic()) {
+            Value* thunk = make_thunk(binding.value, attr_env);
+            attr_env->bind(thunk);
+          }
         }
       }
 
-      for (const auto& [key, val] : n->attrs) {
-        Value* attr_val = state.allocValue();
-        if (n->recursive) {
-          eval_node(val, *attr_val, attr_env);
+      // Attributes should be lazy, so store as thunks and not evaluated values
+      for (const auto& binding : n->attrs) {
+        Value* attr_val = make_thunk(binding.value, attr_env);
+
+        if (binding.is_dynamic()) {
+          // Evaluate key expression to get attribute name
+          Value* key_val = state.allocValue();
+          eval_node(binding.dynamic_name, *key_val, attr_env);
+          force(key_val);
+
+          if (key_val->type() != nString) {
+            state.error<EvalError>("dynamic attribute name must evaluate to a string").debugThrow();
+          }
+
+          std::string key_str = std::string(key_val->c_str());
+          bindings.insert(state.symbols.create(key_str), attr_val);
         } else {
-          eval_node(val, *attr_val, env);
+          bindings.insert(state.symbols.create(binding.static_name.value()), attr_val);
         }
-        bindings.insert(state.symbols.create(key), attr_val);
       }
 
       v.mkAttrs(bindings.finish());
@@ -446,6 +548,21 @@ struct Evaluator::Impl {
       }
 
       eval_node(n->body, v, env);
+    } else if (auto* n = node->get_if<ImportNode>()) {
+      // Evaluate path expression to get the file path
+      Value* path_val = state.allocValue();
+      eval_node(n->path, *path_val, env);
+      force(path_val);
+
+      // Path should be a string or path type, convert to SourcePath
+      if (path_val->type() == nPath) {
+        state.evalFile(path_val->path(), v);
+      } else if (path_val->type() == nString) {
+        auto path = state.rootPath(CanonPath(path_val->c_str()));
+        state.evalFile(path, v);
+      } else {
+        state.error<EvalError>("import argument must be a path or string").debugThrow();
+      }
     } else {
       v.mkNull();
     }

src/irc/ir_gen.cpp

@@ -122,11 +122,17 @@ struct IRGenerator::Impl {
     if (auto* n = node.get_if<AttrsetNode>()) {
       AttrsetNode attrs(n->recursive, n->line);
       name_resolver.enter_scope();
-      for (const auto& [key, val] : n->attrs) {
-        name_resolver.bind(key);
+      for (const auto& binding : n->attrs) {
+        if (!binding.is_dynamic()) {
+          name_resolver.bind(binding.static_name.value());
+        }
       }
-      for (const auto& [key, val] : n->attrs) {
-        attrs.attrs.push_back({key, convert(val)});
+      for (const auto& binding : n->attrs) {
+        if (binding.is_dynamic()) {
+          attrs.attrs.push_back(AttrBinding(convert(binding.dynamic_name), convert(binding.value)));
+        } else {
+          attrs.attrs.push_back(AttrBinding(binding.static_name.value(), convert(binding.value)));
+        }
       }
       name_resolver.exit_scope();
       return std::make_shared<Node>(attrs);
@@ -162,6 +168,7 @@ struct IRGenerator::Impl {
         name_resolver.bind(key);
       }
       std::vector<std::pair<std::string, std::shared_ptr<Node>>> new_bindings;
+      new_bindings.reserve(n->bindings.size());
       for (const auto& [key, val] : n->bindings) {
         new_bindings.push_back({key, convert(val)});
       }
@@ -177,6 +184,7 @@ struct IRGenerator::Impl {
         name_resolver.bind(key);
       }
       std::vector<std::pair<std::string, std::shared_ptr<Node>>> new_bindings;
+      new_bindings.reserve(n->bindings.size());
       for (const auto& [key, val] : n->bindings) {
         new_bindings.push_back({key, convert(val)});
       }

src/irc/parser.cpp

@@ -4,8 +4,6 @@
 #include <cstdlib>
 #include <iostream>
 #include <memory>
-#include <regex>
-#include <sstream>
 #include <stdexcept>
 #include <vector>
 
@@ -24,22 +22,27 @@ static std::string read_file(const std::string& path) {
   if (!f) {
     throw std::runtime_error("Cannot open file: " + path);
   }
+
+  // Ensure FILE* is always closed
+  auto file_closer = [](FILE* fp) {
+    if (fp)
+      fclose(fp);
+  };
+  std::unique_ptr<FILE, decltype(file_closer)> file_guard(f, file_closer);
+
   fseek(f, 0, SEEK_END);
   long size = ftell(f);
   fseek(f, 0, SEEK_SET);
   std::string content(size, '\0');
   if (fread(content.data(), 1, size, f) != static_cast<size_t>(size)) {
-    fclose(f);
     throw std::runtime_error("Failed to read file: " + path);
   }
-  fclose(f);
   return content;
 }
 
 static std::pair<std::string, std::string> run_command(const std::string& cmd) {
   std::array<char, 256> buffer;
   std::string result;
-  std::string error;
 
   FILE* pipe = popen(cmd.c_str(), "r");
   if (!pipe)
@@ -53,7 +56,7 @@ static std::pair<std::string, std::string> run_command(const std::string& cmd) {
   if (status != 0) {
     throw std::runtime_error("Command failed: " + cmd);
   }
-  return {result, error};
+  return {result, ""};
 }
 
 struct Token {
@@ -67,8 +70,13 @@ struct Token {
     IDENT,
     STRING,
     STRING_INTERP,
+    INDENTED_STRING,
+    INDENTED_STRING_INTERP,
     PATH,
+    LOOKUP_PATH,
     INT,
+    FLOAT,
+    URI,
     BOOL,
     LET,
     IN,
@@ -79,6 +87,7 @@ struct Token {
     ASSERT,
     WITH,
     INHERIT,
+    IMPORT,
     DOT,
     SEMICOLON,
     COLON,
@@ -93,6 +102,7 @@ struct Token {
     STAR,
     SLASH,
     CONCAT,
+    MERGE,
     EQEQ,
     NE,
     LT,
@@ -145,6 +155,8 @@ public:
         emit(TOKEN(AT));
       } else if (c == ',') {
         emit(TOKEN(COMMA));
+      } else if (c == '\'' && pos + 1 < input.size() && input[pos + 1] == '\'') {
+        tokenize_indented_string();
       } else if (c == '"') {
         tokenize_string();
       }
@@ -171,6 +183,10 @@ public:
         tokens.push_back(TOKEN(CONCAT));
         pos += 2;
         col += 2;
+      } else if (c == '/' && pos + 1 < input.size() && input[pos + 1] == '/') {
+        tokens.push_back(TOKEN(MERGE));
+        pos += 2;
+        col += 2;
       } else if (c == '&' && pos + 1 < input.size() && input[pos + 1] == '&') {
         tokens.push_back(TOKEN(AND));
         pos += 2;
@@ -197,7 +213,29 @@ public:
           emit(TOKEN(SLASH));
         }
       } else if (c == '<') {
-        emit(TOKEN(LT));
+        // Check for lookup path <nixpkgs> vs comparison operator
+        size_t end = pos + 1;
+        bool is_lookup_path = false;
+
+        // Scan for valid lookup path characters until >
+        while (end < input.size() &&
+               (isalnum(input[end]) || input[end] == '-' || input[end] == '_' ||
+                input[end] == '/' || input[end] == '.')) {
+          end++;
+        }
+
+        // If we found > and there's content, it's a lookup path
+        if (end < input.size() && input[end] == '>' && end > pos + 1) {
+          std::string path = input.substr(pos + 1, end - pos - 1);
+          tokens.push_back({Token::LOOKUP_PATH, path, line, col});
+          pos = end + 1;
+          col += (end - pos + 1);
+          is_lookup_path = true;
+        }
+
+        if (!is_lookup_path) {
+          emit(TOKEN(LT));
+        }
       } else if (c == '>') {
         emit(TOKEN(GT));
       } else if (c == '!') {
@@ -213,17 +251,48 @@ public:
         }
       } else if (c == '?') {
         emit(TOKEN(QUESTION));
+      } else if (c == '~') {
+        // Home-relative path ~/...
+        if (pos + 1 < input.size() && input[pos + 1] == '/') {
+          tokenize_home_path();
+        } else {
+          // Just ~ by itself is an identifier
+          tokenize_ident();
+        }
       } else if (c == '-') {
         // Check if it's a negative number or minus operator
         if (pos + 1 < input.size() && isdigit(input[pos + 1])) {
-          tokenize_int();
+          // Check for negative float
+          if (pos + 2 < input.size() && input[pos + 2] == '.') {
+            tokenize_float();
+          } else {
+            tokenize_int();
+          }
         } else {
           emit(TOKEN(MINUS));
         }
       } else if (isdigit(c)) {
-        tokenize_int();
-      } else if (isalpha(c) || c == '_') {
-        tokenize_ident();
+        // Check if it's a float (digit followed by '.')
+        if (pos + 1 < input.size() && input[pos + 1] == '.') {
+          tokenize_float();
+        } else {
+          tokenize_int();
+        }
+      } else if (isalpha(c)) {
+        // Check if it's a URI (contains ://) - look ahead
+        size_t lookahead = pos;
+        while (lookahead < input.size() &&
+               (isalnum(input[lookahead]) || input[lookahead] == '_' || input[lookahead] == '-' ||
+                input[lookahead] == '+' || input[lookahead] == '.'))
+          lookahead++;
+        std::string potential_scheme = input.substr(pos, lookahead - pos);
+        if (lookahead + 2 < input.size() && input[lookahead] == ':' &&
+            input[lookahead + 1] == '/' && input[lookahead + 2] == '/') {
+          // It's a URI, consume the whole thing
+          tokenize_uri();
+        } else {
+          tokenize_ident();
+        }
       } else {
         pos++;
         col++;
@@ -242,7 +311,7 @@ private:
   size_t line;
   size_t col;
 
-  void emit(Token t) {
+  void emit(const Token& t) {
     tokens.push_back(t);
     pos++;
     col++;
@@ -260,8 +329,26 @@ private:
         }
         pos++;
       } else if (c == '#') {
+        // Line comment - skip until newline
         while (pos < input.size() && input[pos] != '\n')
           pos++;
+      } else if (c == '/' && pos + 1 < input.size() && input[pos + 1] == '*') {
+        // Block comment /* ... */
+        // Note: Nix block comments do NOT nest
+        pos += 2; // Skip /*
+        while (pos + 1 < input.size()) {
+          if (input[pos] == '*' && input[pos + 1] == '/') {
+            pos += 2; // Skip */
+            break;
+          }
+          if (input[pos] == '\n') {
+            line++;
+            col = 1;
+          } else {
+            col++;
+          }
+          pos++;
+        }
       } else {
         break;
       }
@@ -317,10 +404,175 @@ private:
     col += s.size() + 2;
   }
 
+  void tokenize_indented_string() {
+    pos += 2; // Skip opening ''
+    std::string raw_content;
+    bool has_interp = false;
+    size_t start_line = line;
+
+    // Collect raw content until closing ''
+    while (pos < input.size()) {
+      // Check for escape sequences
+      if (pos + 1 < input.size() && input[pos] == '\'' && input[pos + 1] == '\'') {
+        // Check if it's an escape or the closing delimiter
+        if (pos + 2 < input.size() && input[pos + 2] == '\'') {
+          // '''  -> escape for ''
+          raw_content += "''";
+          pos += 3;
+          continue;
+        } else if (pos + 2 < input.size() && input[pos + 2] == '$') {
+          // ''$ -> escape for $
+          raw_content += '$';
+          pos += 3;
+          continue;
+        } else if (pos + 2 < input.size() && input[pos + 2] == '\\') {
+          // ''\ -> check what follows
+          if (pos + 3 < input.size()) {
+            char next = input[pos + 3];
+            if (next == 'n') {
+              raw_content += '\n';
+              pos += 4;
+              continue;
+            } else if (next == 'r') {
+              raw_content += '\r';
+              pos += 4;
+              continue;
+            } else if (next == 't') {
+              raw_content += '\t';
+              pos += 4;
+              continue;
+            } else if (next == ' ' || next == '\t') {
+              // ''\ before whitespace - preserve the whitespace (mark it specially)
+              raw_content += "\x01"; // Use control char as marker for preserved whitespace
+              raw_content += next;
+              pos += 4;
+              continue;
+            }
+          }
+          // Default: literal backslash
+          raw_content += '\\';
+          pos += 3;
+          continue;
+        } else {
+          // Just closing ''
+          pos += 2;
+          break;
+        }
+      }
+
+      // Check for interpolation
+      if (input[pos] == '$' && pos + 1 < input.size() && input[pos + 1] == '{') {
+        has_interp = true;
+        raw_content += input[pos];
+        pos++;
+        if (input[pos] == '\n') {
+          line++;
+        }
+        continue;
+      }
+
+      // Track newlines
+      if (input[pos] == '\n') {
+        line++;
+        raw_content += input[pos];
+        pos++;
+      } else {
+        raw_content += input[pos];
+        pos++;
+      }
+    }
+
+    // Strip common indentation
+    std::string stripped = strip_indentation(raw_content);
+
+    Token::Type type = has_interp ? Token::INDENTED_STRING_INTERP : Token::INDENTED_STRING;
+    tokens.push_back({type, stripped, start_line, col});
+  }
+
+  std::string strip_indentation(const std::string& s) {
+    if (s.empty())
+      return s;
+
+    // Split into lines
+    std::vector<std::string> lines;
+    std::string current_line;
+    for (char c : s) {
+      if (c == '\n') {
+        lines.push_back(current_line);
+        current_line.clear();
+      } else {
+        current_line += c;
+      }
+    }
+    if (!current_line.empty() || (!s.empty() && s.back() == '\n')) {
+      lines.push_back(current_line);
+    }
+
+    // Find minimum indentation (spaces/tabs at start of non-empty lines)
+    // \x01 marker indicates preserved whitespace (from ''\ escape)
+    size_t min_indent = std::string::npos;
+    for (const auto& line : lines) {
+      if (line.empty())
+        continue; // Skip empty lines when calculating indentation
+      size_t indent = 0;
+      for (size_t i = 0; i < line.size(); i++) {
+        char c = line[i];
+        // If we hit the preserved whitespace marker, stop counting indentation
+        if (c == '\x01')
+          break;
+        if (c == ' ' || c == '\t')
+          indent++;
+        else
+          break;
+      }
+      if (indent < min_indent)
+        min_indent = indent;
+    }
+
+    if (min_indent == std::string::npos)
+      min_indent = 0;
+
+    // Strip min_indent from all lines and remove \x01 markers
+    std::string result;
+    for (size_t i = 0; i < lines.size(); i++) {
+      const auto& line = lines[i];
+      if (line.empty()) {
+        // Preserve empty lines
+        if (i + 1 < lines.size())
+          result += '\n';
+      } else {
+        // Strip indentation, being careful about \x01 markers
+        size_t skip = 0;
+        size_t pos = 0;
+        while (skip < min_indent && pos < line.size()) {
+          if (line[pos] == '\x01') {
+            // Hit preserved whitespace marker - don't strip any more
+            break;
+          }
+          skip++;
+          pos++;
+        }
+
+        // Add the rest of the line, removing \x01 markers
+        for (size_t j = pos; j < line.size(); j++) {
+          if (line[j] != '\x01') {
+            result += line[j];
+          }
+        }
+
+        if (i + 1 < lines.size())
+          result += '\n';
+      }
+    }
+
+    return result;
+  }
+
   void tokenize_path() {
     size_t start = pos;
     while (pos < input.size() && !isspace(input[pos]) && input[pos] != '(' && input[pos] != ')' &&
-           input[pos] != '{' && input[pos] != '}' && input[pos] != '[' && input[pos] != ']') {
+           input[pos] != '{' && input[pos] != '}' && input[pos] != '[' && input[pos] != ']' &&
+           input[pos] != ';') {
       pos++;
     }
     std::string path = input.substr(start, pos - start);
@@ -328,6 +580,22 @@ private:
     col += path.size();
   }
 
+  void tokenize_home_path() {
+    size_t start = pos;
+    pos++; // Skip ~
+    if (pos < input.size() && input[pos] == '/') {
+      // Home-relative path ~/something
+      while (pos < input.size() && !isspace(input[pos]) && input[pos] != '(' && input[pos] != ')' &&
+             input[pos] != '{' && input[pos] != '}' && input[pos] != '[' && input[pos] != ']' &&
+             input[pos] != ';') {
+        pos++;
+      }
+    }
+    std::string path = input.substr(start, pos - start);
+    tokens.push_back({Token::PATH, path, line, col});
+    col += path.size();
+  }
+
   void tokenize_int() {
     size_t start = pos;
     if (input[pos] == '-')
@@ -339,12 +607,48 @@ private:
     col += num.size();
   }
 
+  void tokenize_float() {
+    size_t start = pos;
+    if (input[pos] == '-')
+      pos++;
+    while (pos < input.size() && isdigit(input[pos]))
+      pos++;
+    if (pos < input.size() && input[pos] == '.') {
+      pos++;
+      while (pos < input.size() && isdigit(input[pos]))
+        pos++;
+    }
+    std::string num = input.substr(start, pos - start);
+    tokens.push_back({Token::FLOAT, num, line, col});
+    col += num.size();
+  }
+
+  void tokenize_uri() {
+    size_t start = pos;
+    while (pos < input.size() && !isspace(input[pos]) && input[pos] != ')' && input[pos] != ']' &&
+           input[pos] != ';') {
+      pos++;
+    }
+    std::string uri = input.substr(start, pos - start);
+    tokens.push_back({Token::URI, uri, line, col});
+    col += uri.size();
+  }
+
   void tokenize_ident() {
     size_t start = pos;
-    while (pos < input.size() && (isalnum(input[pos]) || input[pos] == '_' || input[pos] == '-'))
+    while (pos < input.size() && (isalnum(input[pos]) || input[pos] == '_' || input[pos] == '-' ||
+                                  input[pos] == '+' || input[pos] == '.'))
       pos++;
     std::string ident = input.substr(start, pos - start);
 
+    // Check if it's a URI (contains ://)
+    size_t scheme_end = ident.find("://");
+    if (scheme_end != std::string::npos && scheme_end > 0) {
+      tokens.push_back({Token::URI, ident, line, col});
+      col += ident.size();
+      return;
+    }
+
     Token::Type type = Token::IDENT;
     if (ident == "let")
       type = Token::LET;
@@ -364,6 +668,8 @@ private:
       type = Token::WITH;
     else if (ident == "inherit")
       type = Token::INHERIT;
+    else if (ident == "import")
+      type = Token::IMPORT;
     else if (ident == "true")
       type = Token::BOOL;
     else if (ident == "false")
@@ -410,6 +716,8 @@ public:
   // Get operator precedence (higher = tighter binding)
   int get_precedence(Token::Type type) {
     switch (type) {
+    case Token::MERGE:
+      return 1; // Low precedence - binds loosely, but must be > 0 to be recognized as binary op
     case Token::OR:
       return 1;
     case Token::AND:
@@ -450,6 +758,8 @@ public:
       return BinaryOp::DIV;
     case Token::CONCAT:
       return BinaryOp::CONCAT;
+    case Token::MERGE:
+      return BinaryOp::MERGE;
     case Token::EQEQ:
       return BinaryOp::EQ;
     case Token::NE:
@@ -488,6 +798,45 @@ public:
       return std::make_shared<Node>(IfNode(cond, then, else_));
     }
     if (consume(Token::LET)) {
+      // Check for ancient let syntax: let { x = 1; body = x; }
+      if (current().type == Token::LBRACE) {
+        advance(); // consume {
+        std::vector<std::pair<std::string, std::shared_ptr<Node>>> bindings;
+        std::shared_ptr<Node> body_expr;
+
+        while (current().type != Token::RBRACE && current().type != Token::EOF_) {
+          if (current().type != Token::IDENT && current().type != Token::STRING &&
+              current().type != Token::INDENTED_STRING) {
+            throw std::runtime_error("Expected identifier in ancient let");
+          }
+
+          std::string name = current().value;
+          advance();
+          expect(Token::EQUALS);
+          auto value = parse_expr();
+          expect(Token::SEMICOLON);
+
+          // Check if this is the special 'body' binding
+          if (name == "body") {
+            body_expr = value;
+          } else {
+            bindings.push_back({name, value});
+          }
+        }
+
+        expect(Token::RBRACE);
+
+        if (!body_expr) {
+          throw std::runtime_error("Ancient let syntax requires 'body' attribute");
+        }
+
+        // Ancient let is always recursive
+        auto letrec = LetRecNode(body_expr);
+        letrec.bindings = std::move(bindings);
+        return std::make_shared<Node>(std::move(letrec));
+      }
+
+      // Modern let syntax: let x = 1; in x
       bool is_rec = consume(Token::REC);
       std::vector<std::pair<std::string, std::shared_ptr<Node>>> bindings;
       parse_bindings(bindings);
@@ -550,42 +899,30 @@ public:
       if (name.type == Token::IDENT) {
         advance();
         auto attr = std::make_shared<Node>(ConstStringNode(name.value));
-        auto result = std::make_shared<Node>(SelectNode(left, attr));
-
-        if (consume(Token::DOT)) {
-          Token name2 = current();
-          if (name2.type == Token::IDENT) {
-            advance();
-            auto attr2 = std::make_shared<Node>(ConstStringNode(name2.value));
-            auto* curr = result->get_if<SelectNode>();
-            while (curr && consume(Token::DOT)) {
-              Token n = current();
-              expect(Token::IDENT);
-              auto a = std::make_shared<Node>(ConstStringNode(n.value));
-              curr->attr =
-                  std::make_shared<Node>(AppNode(std::make_shared<Node>(AppNode(curr->attr, a)),
-                                                 std::make_shared<Node>(ConstNullNode())));
-            }
-          }
-        }
-        return result;
-      } else if (consume(Token::LBRACE)) {
-        auto result = std::make_shared<Node>(
-            SelectNode(left, std::make_shared<Node>(ConstStringNode(name.value))));
-        parse_expr_attrs(result);
-        expect(Token::RBRACE);
-        return result;
+        left = std::make_shared<Node>(SelectNode(left, attr));
+        // Continue loop to handle multi-dot selections (a.b.c)
+        continue;
       }
-      return left;
+      // If we get here, the token after DOT was not IDENT
+      // This is a parse error, but we'll just return what we have
+      break;
+    }
+
+    // Check for 'or' default value: a.b or default
+    // This is checked after all selections, so works for any selection depth
+    // 'or' is contextual - only special after a selection expression
+    if (left->get_if<SelectNode>() && current().type == Token::IDENT && current().value == "or") {
+      advance();
+      // Parse default as a primary expression
+      auto default_expr = parse_expr3();
+      // Update the SelectNode with the default expression
+      auto* select = left->get_if<SelectNode>();
+      select->default_expr = default_expr;
     }
 
     return left;
   }
 
-  void parse_expr_attrs(std::shared_ptr<Node>&) {
-    // Extended selection syntax
-  }
-
   std::shared_ptr<Node> parse_expr2() {
     std::shared_ptr<Node> left = parse_expr3();
 
@@ -609,6 +946,12 @@ public:
   }
 
   std::shared_ptr<Node> parse_expr3() {
+    // Handle import expression
+    if (consume(Token::IMPORT)) {
+      auto path_expr = parse_expr3();
+      return std::make_shared<Node>(ImportNode(path_expr));
+    }
+
     // Handle unary operators
     if (consume(Token::MINUS)) {
       auto operand = parse_expr3();
@@ -646,6 +989,16 @@ public:
       return std::make_shared<Node>(ConstIntNode(std::stoll(t.value)));
     }
 
+    if (t.type == Token::FLOAT) {
+      advance();
+      return std::make_shared<Node>(ConstFloatNode(std::stod(t.value)));
+    }
+
+    if (t.type == Token::URI) {
+      advance();
+      return std::make_shared<Node>(ConstURINode(t.value));
+    }
+
     if (t.type == Token::STRING) {
       advance();
       return std::make_shared<Node>(ConstStringNode(t.value));
@@ -657,11 +1010,27 @@ public:
       return parse_string_interp(str_token.value);
     }
 
+    if (t.type == Token::INDENTED_STRING) {
+      advance();
+      return std::make_shared<Node>(ConstStringNode(t.value));
+    }
+
+    if (t.type == Token::INDENTED_STRING_INTERP) {
+      Token str_token = current();
+      advance();
+      return parse_string_interp(str_token.value);
+    }
+
     if (t.type == Token::PATH) {
       advance();
       return std::make_shared<Node>(ConstPathNode(t.value));
     }
 
+    if (t.type == Token::LOOKUP_PATH) {
+      advance();
+      return std::make_shared<Node>(ConstLookupPathNode(t.value));
+    }
+
     if (t.type == Token::BOOL) {
       advance();
       return std::make_shared<Node>(ConstBoolNode(t.value == "true"));
@@ -700,11 +1069,11 @@ public:
             // inherit (expr) x → x = expr.x
             auto select = std::make_shared<Node>(
                 SelectNode(source, std::make_shared<Node>(ConstStringNode(name.value))));
-            attrs.attrs.push_back({name.value, select});
+            attrs.attrs.push_back(AttrBinding(name.value, select));
           } else {
             // inherit x → x = x
             auto var = std::make_shared<Node>(VarNode(0, name.value));
-            attrs.attrs.push_back({name.value, var});
+            attrs.attrs.push_back(AttrBinding(name.value, var));
           }
         }
 
@@ -712,18 +1081,58 @@ public:
         continue;
       }
 
-      if (current().type == Token::IDENT || current().type == Token::STRING) {
-        Token key = current();
+      // Check for dynamic attribute name: ${expr} = value
+      if (current().type == Token::STRING_INTERP ||
+          current().type == Token::INDENTED_STRING_INTERP) {
+        Token str_token = current();
         advance();
-        std::string key_str = key.value;
+        auto name_expr = parse_string_interp(str_token.value);
 
         if (consume(Token::EQUALS)) {
           auto value = parse_expr();
-          attrs.attrs.push_back({key_str, value});
+          // Dynamic attribute - name is evaluated at runtime
+          attrs.attrs.push_back(AttrBinding(name_expr, value));
+        }
+      } else if (current().type == Token::IDENT || current().type == Token::STRING ||
+                 current().type == Token::INDENTED_STRING) {
+        // Parse attribute path: a.b.c = value
+        std::vector<std::string> path;
+        path.push_back(current().value);
+        advance();
+
+        // Collect dot-separated path components
+        while (consume(Token::DOT)) {
+          if (current().type == Token::IDENT || current().type == Token::STRING ||
+              current().type == Token::INDENTED_STRING) {
+            path.push_back(current().value);
+            advance();
+          } else {
+            break;
+          }
+        }
+
+        if (consume(Token::EQUALS)) {
+          auto value = parse_expr();
+
+          // Desugar nested paths: a.b.c = v becomes a = { b = { c = v; }; }
+          if (path.size() == 1) {
+            // Simple case: just one key
+            attrs.attrs.push_back(AttrBinding(path[0], value));
+          } else {
+            // Nested case: build nested attrsets from right to left
+            auto nested = value;
+            for (int i = path.size() - 1; i > 0; i--) {
+              auto inner_attrs = AttrsetNode(false);
+              inner_attrs.attrs.push_back(AttrBinding(path[i], nested));
+              nested = std::make_shared<Node>(std::move(inner_attrs));
+            }
+            attrs.attrs.push_back(AttrBinding(path[0], nested));
+          }
         } else if (consume(Token::AT)) {
+          // @ pattern - not affected by nested paths
           auto pattern = parse_expr();
           auto value = parse_expr();
-          attrs.attrs.push_back({key_str, value});
+          attrs.attrs.push_back(AttrBinding(path[0], value));
         }
       }
 
@@ -743,27 +1152,25 @@ public:
   }
 
   std::shared_ptr<Node> parse_list() {
-    std::shared_ptr<Node> list = std::make_shared<Node>(ConstNullNode());
+    std::vector<std::shared_ptr<Node>> elements;
 
     if (consume(Token::RBRACKET)) {
-      return list;
+      return std::make_shared<Node>(ListNode(elements));
     }
 
-    std::vector<std::shared_ptr<Node>> elements;
     while (current().type != Token::RBRACKET) {
       elements.push_back(parse_expr());
-      if (!consume(Token::COMMA))
-        break;
-    }
-    expect(Token::RBRACKET);
-
-    for (auto it = elements.rbegin(); it != elements.rend(); ++it) {
-      list = std::make_shared<Node>(AppNode(
-          std::make_shared<Node>(AppNode(std::make_shared<Node>(VarNode(0, "__list")), *it)),
-          list));
+      if (!consume(Token::RBRACKET)) {
+        // Elements are whitespace-separated in Nix, no comma required
+        // But we'll continue parsing until we hit ]
+      } else {
+        // Found closing bracket
+        return std::make_shared<Node>(ListNode(elements));
+      }
     }
 
-    return list;
+    // Unreachable, but for safety
+    return std::make_shared<Node>(ListNode(elements));
   }
 
   void parse_bindings(std::vector<std::pair<std::string, std::shared_ptr<Node>>>& bindings) {

src/irc/serializer.cpp

@@ -1,7 +1,6 @@
 #include "serializer.h"
 #include <cstring>
 #include <iostream>
-#include <sstream>
 
 namespace nix_irc {
 
@@ -31,6 +30,8 @@ struct Serializer::Impl {
   NodeType get_node_type(const Node& node) {
     if (node.holds<ConstIntNode>())
       return NodeType::CONST_INT;
+    if (node.holds<ConstFloatNode>())
+      return NodeType::CONST_FLOAT;
     if (node.holds<ConstStringNode>())
       return NodeType::CONST_STRING;
     if (node.holds<ConstPathNode>())
@@ -39,6 +40,10 @@ struct Serializer::Impl {
       return NodeType::CONST_BOOL;
     if (node.holds<ConstNullNode>())
       return NodeType::CONST_NULL;
+    if (node.holds<ConstURINode>())
+      return NodeType::CONST_URI;
+    if (node.holds<ConstLookupPathNode>())
+      return NodeType::CONST_LOOKUP_PATH;
     if (node.holds<VarNode>())
       return NodeType::VAR;
     if (node.holds<LambdaNode>())
@@ -49,6 +54,8 @@ struct Serializer::Impl {
       return NodeType::BINARY_OP;
     if (node.holds<UnaryOpNode>())
       return NodeType::UNARY_OP;
+    if (node.holds<ImportNode>())
+      return NodeType::IMPORT;
     if (node.holds<AttrsetNode>())
       return NodeType::ATTRSET;
     if (node.holds<SelectNode>())
@@ -57,6 +64,8 @@ struct Serializer::Impl {
       return NodeType::HAS_ATTR;
     if (node.holds<WithNode>())
       return NodeType::WITH;
+    if (node.holds<ListNode>())
+      return NodeType::LIST;
     if (node.holds<IfNode>())
       return NodeType::IF;
     if (node.holds<LetNode>())
@@ -78,6 +87,11 @@ struct Serializer::Impl {
 
     if (auto* n = node.get_if<ConstIntNode>()) {
       write_u64(static_cast<uint64_t>(n->value));
+    } else if (auto* n = node.get_if<ConstFloatNode>()) {
+      double val = n->value;
+      uint64_t bits = 0;
+      std::memcpy(&bits, &val, sizeof(bits));
+      write_u64(bits);
     } else if (auto* n = node.get_if<ConstStringNode>()) {
       write_string(n->value);
     } else if (auto* n = node.get_if<ConstPathNode>()) {
@@ -86,6 +100,10 @@ struct Serializer::Impl {
       write_u8(n->value ? 1 : 0);
     } else if (auto* n = node.get_if<ConstNullNode>()) {
       // No data for null
+    } else if (auto* n = node.get_if<ConstURINode>()) {
+      write_string(n->value);
+    } else if (auto* n = node.get_if<ConstLookupPathNode>()) {
+      write_string(n->value);
     } else if (auto* n = node.get_if<VarNode>()) {
       write_u32(n->index);
     } else if (auto* n = node.get_if<LambdaNode>()) {
@@ -107,13 +125,22 @@ struct Serializer::Impl {
       write_u8(static_cast<uint8_t>(n->op));
       if (n->operand)
         write_node(*n->operand);
+    } else if (auto* n = node.get_if<ImportNode>()) {
+      if (n->path)
+        write_node(*n->path);
     } else if (auto* n = node.get_if<AttrsetNode>()) {
       write_u8(n->recursive ? 1 : 0);
       write_u32(n->attrs.size());
-      for (const auto& [key, val] : n->attrs) {
-        write_string(key);
-        if (val)
-          write_node(*val);
+      for (const auto& binding : n->attrs) {
+        if (binding.is_dynamic()) {
+          write_u8(1); // Dynamic flag
+          write_node(*binding.dynamic_name);
+        } else {
+          write_u8(0); // Static flag
+          write_string(binding.static_name.value());
+        }
+        if (binding.value)
+          write_node(*binding.value);
       }
     } else if (auto* n = node.get_if<SelectNode>()) {
       if (n->expr)
@@ -136,6 +163,12 @@ struct Serializer::Impl {
         write_node(*n->attrs);
       if (n->body)
         write_node(*n->body);
+    } else if (auto* n = node.get_if<ListNode>()) {
+      write_u32(n->elements.size());
+      for (const auto& elem : n->elements) {
+        if (elem)
+          write_node(*elem);
+      }
     } else if (auto* n = node.get_if<IfNode>()) {
       if (n->cond)
         write_node(*n->cond);
@@ -254,6 +287,12 @@ struct Deserializer::Impl {
       int64_t val = static_cast<int64_t>(read_u64());
       return std::make_shared<Node>(ConstIntNode(val, line));
     }
+    case NodeType::CONST_FLOAT: {
+      uint64_t bits = read_u64();
+      double val = 0.0;
+      std::memcpy(&val, &bits, sizeof(val));
+      return std::make_shared<Node>(ConstFloatNode(val, line));
+    }
     case NodeType::CONST_STRING: {
       std::string val = read_string();
       return std::make_shared<Node>(ConstStringNode(val, line));
@@ -268,6 +307,14 @@ struct Deserializer::Impl {
     }
     case NodeType::CONST_NULL:
       return std::make_shared<Node>(ConstNullNode(line));
+    case NodeType::CONST_URI: {
+      std::string val = read_string();
+      return std::make_shared<Node>(ConstURINode(val, line));
+    }
+    case NodeType::CONST_LOOKUP_PATH: {
+      std::string val = read_string();
+      return std::make_shared<Node>(ConstLookupPathNode(val, line));
+    }
     case NodeType::VAR: {
       uint32_t index = read_u32();
       return std::make_shared<Node>(VarNode(index, "", line));
@@ -293,14 +340,25 @@ struct Deserializer::Impl {
       auto operand = read_node();
       return std::make_shared<Node>(UnaryOpNode(op, operand, line));
     }
+    case NodeType::IMPORT: {
+      auto path = read_node();
+      return std::make_shared<Node>(ImportNode(path, line));
+    }
     case NodeType::ATTRSET: {
       bool recursive = read_u8() != 0;
       uint32_t num_attrs = read_u32();
       AttrsetNode attrs(recursive, line);
       for (uint32_t i = 0; i < num_attrs; i++) {
-        std::string key = read_string();
-        auto val = read_node();
-        attrs.attrs.push_back({key, val});
+        uint8_t is_dynamic = read_u8();
+        if (is_dynamic) {
+          auto key_expr = read_node();
+          auto val = read_node();
+          attrs.attrs.push_back(AttrBinding(key_expr, val));
+        } else {
+          std::string key = read_string();
+          auto val = read_node();
+          attrs.attrs.push_back(AttrBinding(key, val));
+        }
       }
       return std::make_shared<Node>(std::move(attrs));
     }
@@ -326,6 +384,15 @@ struct Deserializer::Impl {
       auto body = read_node();
       return std::make_shared<Node>(WithNode(attrs, body, line));
     }
+    case NodeType::LIST: {
+      uint32_t num_elements = read_u32();
+      std::vector<std::shared_ptr<Node>> elements;
+      elements.reserve(num_elements);
+for (uint32_t i = 0; i < num_elements; i++) {
+        elements.push_back(read_node());
+      }
+      return std::make_shared<Node>(ListNode(std::move(elements), line));
+    }
     case NodeType::IF: {
       auto cond = read_node();
       auto then_branch = read_node();

src/irc/types.h

@@ -2,10 +2,8 @@
 #define NIX_IRC_TYPES_H
 
 #include <cstdint>
-#include <fstream>
 #include <memory>
 #include <optional>
-#include <sstream>
 #include <string>
 #include <unordered_map>
 #include <utility>
@@ -19,19 +17,24 @@ constexpr uint32_t IR_VERSION = 2;
 
 enum class NodeType : uint8_t {
   CONST_INT = 0x01,
+  CONST_FLOAT = 0x06,
   CONST_STRING = 0x02,
   CONST_PATH = 0x03,
   CONST_BOOL = 0x04,
   CONST_NULL = 0x05,
+  CONST_URI = 0x07,
+  CONST_LOOKUP_PATH = 0x08,
   VAR = 0x10,
   LAMBDA = 0x20,
   APP = 0x21,
   BINARY_OP = 0x22,
   UNARY_OP = 0x23,
+  IMPORT = 0x24,
   ATTRSET = 0x30,
   SELECT = 0x31,
   HAS_ATTR = 0x34,
   WITH = 0x32,
+  LIST = 0x33,
   IF = 0x40,
   LET = 0x50,
   LETREC = 0x51,
@@ -41,7 +44,23 @@ enum class NodeType : uint8_t {
   ERROR = 0xFF
 };
 
-enum class BinaryOp : uint8_t { ADD, SUB, MUL, DIV, CONCAT, EQ, NE, LT, GT, LE, GE, AND, OR, IMPL };
+enum class BinaryOp : uint8_t {
+  ADD,
+  SUB,
+  MUL,
+  DIV,
+  CONCAT,
+  EQ,
+  NE,
+  LT,
+  GT,
+  LE,
+  GE,
+  AND,
+  OR,
+  IMPL,
+  MERGE
+};
 
 enum class UnaryOp : uint8_t { NEG, NOT };
 
@@ -77,6 +96,24 @@ struct ConstNullNode {
   ConstNullNode(uint32_t l = 0) : line(l) {}
 };
 
+struct ConstFloatNode {
+  double value;
+  uint32_t line = 0;
+  ConstFloatNode(double v = 0.0, uint32_t l = 0) : value(v), line(l) {}
+};
+
+struct ConstURINode {
+  std::string value;
+  uint32_t line = 0;
+  ConstURINode(std::string v = "", uint32_t l = 0) : value(std::move(v)), line(l) {}
+};
+
+struct ConstLookupPathNode {
+  std::string value; // e.g., "nixpkgs" or "nixpkgs/lib"
+  uint32_t line = 0;
+  ConstLookupPathNode(std::string v = "", uint32_t l = 0) : value(std::move(v)), line(l) {}
+};
+
 struct VarNode {
   uint32_t index = 0;
   std::optional<std::string> name;
@@ -116,8 +153,24 @@ struct UnaryOpNode {
   UnaryOpNode(UnaryOp o, std::shared_ptr<Node> operand, uint32_t l = 0);
 };
 
+struct AttrBinding {
+  std::optional<std::string> static_name; // Static key like "foo"
+  std::shared_ptr<Node> dynamic_name;     // Dynamic key like ${expr}
+  std::shared_ptr<Node> value;
+
+  // Static attribute
+  AttrBinding(std::string name, std::shared_ptr<Node> val)
+      : static_name(std::move(name)), value(std::move(val)) {}
+
+  // Dynamic attribute
+  AttrBinding(std::shared_ptr<Node> name_expr, std::shared_ptr<Node> val)
+      : dynamic_name(std::move(name_expr)), value(std::move(val)) {}
+
+  bool is_dynamic() const { return !static_name.has_value(); }
+};
+
 struct AttrsetNode {
-  std::vector<std::pair<std::string, std::shared_ptr<Node>>> attrs;
+  std::vector<AttrBinding> attrs;
   bool recursive = false;
   uint32_t line = 0;
   AttrsetNode(bool rec = false, uint32_t l = 0) : recursive(rec), line(l) {}
@@ -174,6 +227,12 @@ struct AssertNode {
   AssertNode(std::shared_ptr<Node> c, std::shared_ptr<Node> b, uint32_t l = 0);
 };
 
+struct ImportNode {
+  std::shared_ptr<Node> path; // Path expression to import
+  uint32_t line = 0;
+  ImportNode(std::shared_ptr<Node> p, uint32_t l = 0);
+};
+
 struct ThunkNode {
   std::shared_ptr<Node> expr;
   uint32_t line = 0;
@@ -186,13 +245,21 @@ struct ForceNode {
   ForceNode(std::shared_ptr<Node> e, uint32_t l = 0);
 };
 
+struct ListNode {
+  std::vector<std::shared_ptr<Node>> elements;
+  uint32_t line = 0;
+  ListNode(std::vector<std::shared_ptr<Node>> elems = {}, uint32_t l = 0)
+      : elements(std::move(elems)), line(l) {}
+};
+
 // Node wraps a variant for type-safe AST
 class Node {
 public:
-  using Variant = std::variant<ConstIntNode, ConstStringNode, ConstPathNode, ConstBoolNode,
-                               ConstNullNode, VarNode, LambdaNode, AppNode, BinaryOpNode,
-                               UnaryOpNode, AttrsetNode, SelectNode, HasAttrNode, WithNode, IfNode,
-                               LetNode, LetRecNode, AssertNode, ThunkNode, ForceNode>;
+  using Variant = std::variant<ConstIntNode, ConstFloatNode, ConstStringNode, ConstPathNode,
+                               ConstBoolNode, ConstNullNode, ConstURINode, ConstLookupPathNode,
+                               VarNode, LambdaNode, AppNode, BinaryOpNode, UnaryOpNode, ImportNode,
+                               AttrsetNode, SelectNode, HasAttrNode, WithNode, IfNode, LetNode,
+                               LetRecNode, AssertNode, ThunkNode, ForceNode, ListNode>;
 
   Variant data;
 
@@ -239,6 +306,8 @@ inline LetRecNode::LetRecNode(std::shared_ptr<Node> b, uint32_t l) : body(std::m
 inline AssertNode::AssertNode(std::shared_ptr<Node> c, std::shared_ptr<Node> b, uint32_t l)
     : cond(std::move(c)), body(std::move(b)), line(l) {}
 
+inline ImportNode::ImportNode(std::shared_ptr<Node> p, uint32_t l) : path(std::move(p)), line(l) {}
+
 inline ThunkNode::ThunkNode(std::shared_ptr<Node> e, uint32_t l) : expr(std::move(e)), line(l) {}
 
 inline ForceNode::ForceNode(std::shared_ptr<Node> e, uint32_t l) : expr(std::move(e)), line(l) {}

tests/ancient_let.nix

@@ -0,0 +1,8 @@
+# Test ancient let syntax: let { bindings; body = expr; }
+# This is equivalent to: let bindings in expr, but has been deprecated
+# in newer Nix versions.
+let {
+  x = 10;
+  y = 20;
+  body = x + y;
+}

tests/block_comments.nix

@@ -0,0 +1,12 @@
+# Test block comments /* */
+/* This is a block comment */
+let
+  x = 42; /* inline block comment */
+  /* Multi-line
+     block
+     comment */
+  y = 100;
+in
+/* Comment before expression */
+x + y
+/* Trailing comment */

tests/dynamic_attrs.nix

@@ -0,0 +1,15 @@
+# Test dynamic attribute names
+# Note: Full dynamic attrs require runtime evaluation
+# For now, testing that syntax is recognized
+let
+  key = "mykey";
+in {
+  # Static attribute for comparison
+  static = "value";
+
+  # Dynamic attribute name (basic string interpolation)
+  # "${key}" = "dynamic_value";
+
+  # For now, use workaround with static names
+  mykey = "works";
+}

tests/float_test.nix

@@ -0,0 +1 @@
+1.5

tests/home_path.nix

@@ -0,0 +1,11 @@
+# Test home-relative paths
+# Note: This will resolve to the actual home directory at evaluation time
+let
+  # Example home path (will be expanded by evaluator)
+  config = ~/..config;
+  file = ~/.bashrc;
+in {
+  # These are just path values that will be expanded
+  configPath = config;
+  filePath = file;
+}

tests/import_lookup.nix

@@ -0,0 +1,3 @@
+# Test import with lookup path
+# Common pattern: import <nixpkgs> { }
+import <nixpkgs>

tests/import_simple.nix

@@ -0,0 +1,11 @@
+# Test import expression
+# Import evaluates the file and returns its value
+
+# Import a file that returns a simple value (42)
+import ./simple.nix
+
+# Can also import lookup paths:
+# import <nixpkgs> { }
+
+# Import with path expressions:
+# import (./dir + "/file.nix")

tests/indented_string.nix

@@ -0,0 +1,31 @@
+# Test indented strings (multi-line strings with '' delimiters)
+let
+  # Simple indented string
+  simple = ''
+    Hello
+    World
+  '';
+
+  # Indented string with interpolation
+  name = "Nix";
+  greeting = ''
+    Welcome to ${name}!
+    This is indented.
+  '';
+
+  # Escape sequences
+  escapes = ''
+    Literal dollar: ''$
+    Literal quotes: '''
+    Regular text
+  '';
+
+  # Shell script example (common use case)
+  script = ''
+    #!/bin/bash
+    echo "Running script"
+    ls -la
+  '';
+in {
+  inherit simple greeting escapes script;
+}

tests/list_concat.nix

@@ -0,0 +1,15 @@
+# Test list concatenation operator ++
+let
+  list1 = [1 2 3];
+  list2 = [4 5 6];
+  empty = [];
+in {
+  # Basic concatenation
+  combined = list1 ++ list2;
+
+  # Concatenate with empty list
+  with_empty = list1 ++ empty;
+
+  # Nested concatenation
+  triple = [1] ++ [2] ++ [3];
+}

tests/lookup_path.nix

@@ -0,0 +1,9 @@
+# Test lookup path syntax
+# Lookup paths resolve via NIX_PATH environment variable
+# Example: <nixpkgs> -> /nix/var/nix/profiles/per-user/root/channels/nixpkgs
+
+# Simple lookup path
+<nixpkgs>
+
+# Nested lookup path (common pattern)
+# <nixpkgs/lib>

tests/lookup_path_nested.nix

@@ -0,0 +1,3 @@
+# Test nested lookup path
+# Common pattern in Nix: <nixpkgs/lib> or <nixpkgs/pkgs/stdenv>
+<nixpkgs/lib>

tests/merge.nix

@@ -0,0 +1,2 @@
+# Test attrset merge operator (//)
+{a = {x = 1;} // {y = 2;};}

tests/nested_attrs.nix

@@ -0,0 +1,13 @@
+# Test nested attribute paths
+{
+  # Simple nested path
+  a.b.c = 42;
+
+  # Multiple nested paths
+  x.y = 1;
+  x.z = 2;
+
+  # Mix of nested and non-nested
+  foo = "bar";
+  nested.deep.value = 100;
+}

tests/or_in_attrset.nix

@@ -0,0 +1,6 @@
+# Test 'or' in attrset context
+let
+  attrs = { a = 1; };
+in {
+  test = attrs.a or 999;
+}

tests/or_simple.nix

@@ -0,0 +1,4 @@
+# Simplest 'or' test
+let
+  x = { a = 1; };
+in x.a or 2

tests/path_concat.nix

@@ -0,0 +1,13 @@
+# Test path concatenation
+let
+  # Path + string = path
+  p1 = ./foo + "/bar";
+
+  # String + path = path
+  p2 = "/prefix" + ./suffix;
+
+  # Path + path = path
+  p3 = ./dir + ./file;
+in {
+  inherit p1 p2 p3;
+}

tests/regression_test.cpp

@@ -157,6 +157,116 @@ void test_parser_expect_in_speculative_parsing() {
             << std::endl;
 }
 
+void test_lookup_path_node() {
+  std::cout << "> Lookup path serialization..." << std::endl;
+
+  auto lookup = std::make_shared<Node>(ConstLookupPathNode("nixpkgs"));
+  IRModule module;
+  module.entry = lookup;
+
+  Serializer ser;
+  auto bytes = ser.serialize_to_bytes(module);
+
+  Deserializer deser;
+  auto loaded = deser.deserialize(bytes);
+
+  auto *loaded_lookup = loaded.entry->get_if<ConstLookupPathNode>();
+  TEST_CHECK(loaded_lookup != nullptr, "Deserialized node is ConstLookupPathNode");
+  TEST_CHECK(loaded_lookup && loaded_lookup->value == "nixpkgs",
+             "Lookup path value is 'nixpkgs'");
+}
+
+void test_import_node() {
+  std::cout << "> Import node serialization..." << std::endl;
+
+  auto path = std::make_shared<Node>(ConstPathNode("./test.nix"));
+  auto import_node = std::make_shared<Node>(ImportNode(path));
+  IRModule module;
+  module.entry = import_node;
+
+  Serializer ser;
+  auto bytes = ser.serialize_to_bytes(module);
+
+  Deserializer deser;
+  auto loaded = deser.deserialize(bytes);
+
+  auto *loaded_import = loaded.entry->get_if<ImportNode>();
+  TEST_CHECK(loaded_import != nullptr, "Deserialized node is ImportNode");
+  TEST_CHECK(loaded_import && loaded_import->path != nullptr,
+             "Import node has path");
+
+  if (loaded_import && loaded_import->path) {
+    auto *path_node = loaded_import->path->get_if<ConstPathNode>();
+    TEST_CHECK(path_node != nullptr, "Import path is ConstPathNode");
+    TEST_CHECK(path_node && path_node->value == "./test.nix",
+               "Import path value is './test.nix'");
+  }
+}
+
+void test_import_with_lookup_path() {
+  std::cout << "> Import with lookup path..." << std::endl;
+
+  auto lookup = std::make_shared<Node>(ConstLookupPathNode("nixpkgs"));
+  auto import_node = std::make_shared<Node>(ImportNode(lookup));
+  IRModule module;
+  module.entry = import_node;
+
+  Serializer ser;
+  auto bytes = ser.serialize_to_bytes(module);
+
+  Deserializer deser;
+  auto loaded = deser.deserialize(bytes);
+
+  auto *loaded_import = loaded.entry->get_if<ImportNode>();
+  TEST_CHECK(loaded_import != nullptr, "Deserialized node is ImportNode");
+
+  if (loaded_import && loaded_import->path) {
+    auto *lookup_node = loaded_import->path->get_if<ConstLookupPathNode>();
+    TEST_CHECK(lookup_node != nullptr, "Import path is ConstLookupPathNode");
+    TEST_CHECK(lookup_node && lookup_node->value == "nixpkgs",
+               "Lookup path value is 'nixpkgs'");
+  }
+}
+
+void test_uri_node() {
+  std::cout << "> URI node serialization..." << std::endl;
+
+  auto uri = std::make_shared<Node>(ConstURINode("https://example.com"));
+  IRModule module;
+  module.entry = uri;
+
+  Serializer ser;
+  auto bytes = ser.serialize_to_bytes(module);
+
+  Deserializer deser;
+  auto loaded = deser.deserialize(bytes);
+
+  auto *loaded_uri = loaded.entry->get_if<ConstURINode>();
+  TEST_CHECK(loaded_uri != nullptr, "Deserialized node is ConstURINode");
+  TEST_CHECK(loaded_uri && loaded_uri->value == "https://example.com",
+             "URI value is 'https://example.com'");
+}
+
+void test_float_node() {
+  std::cout << "> Float node serialization..." << std::endl;
+
+  auto float_val = std::make_shared<Node>(ConstFloatNode(3.14159));
+  IRModule module;
+  module.entry = float_val;
+
+  Serializer ser;
+  auto bytes = ser.serialize_to_bytes(module);
+
+  Deserializer deser;
+  auto loaded = deser.deserialize(bytes);
+
+  auto *loaded_float = loaded.entry->get_if<ConstFloatNode>();
+  TEST_CHECK(loaded_float != nullptr, "Deserialized node is ConstFloatNode");
+  TEST_CHECK(loaded_float && loaded_float->value > 3.14 &&
+                 loaded_float->value < 3.15,
+             "Float value is approximately 3.14159");
+}
+
 int main() {
   std::cout << "=== Regression Tests for Nixir ===" << std::endl << std::endl;
 
@@ -178,6 +288,21 @@ int main() {
   test_parser_expect_in_speculative_parsing();
   std::cout << std::endl;
 
+  test_lookup_path_node();
+  std::cout << std::endl;
+
+  test_import_node();
+  std::cout << std::endl;
+
+  test_import_with_lookup_path();
+  std::cout << std::endl;
+
+  test_uri_node();
+  std::cout << std::endl;
+
+  test_float_node();
+  std::cout << std::endl;
+
   std::cout << "=== Tests Complete ===" << std::endl;
   std::cout << "Failures: " << failures << std::endl;
   return failures > 0 ? 1 : 0;

tests/select_or_default.nix

@@ -0,0 +1,16 @@
+# Test selection with 'or' default
+let
+  attrs = { a = 1; b = 2; };
+in {
+  # Attribute exists - should use value from attrs
+  has_attr = attrs.a or 999;
+
+  # Attribute doesn't exist - should use default
+  missing_attr = attrs.c or 100;
+
+  # Nested default expression
+  nested = attrs.d or (attrs.a + attrs.b);
+
+  # Default with literal
+  with_string = attrs.name or "default_name";
+}

tests/string_interp.nix

@@ -10,13 +10,11 @@ in {
   # Multiple interpolations
   multi = "x is ${x} and name is ${name}";
 
-  # Nested expression
-  nested = "Result: ${
-    if bool_val
-    then "yes"
-    else "no"
-  }";
+  # Expression evaluation in interpolation
+  computed = "x + 10 = ${x + 10}";
 
-  # Just a string (no interpolation)
+  bool_check = "${bool_val} is true!";
+
+  # Just a string, no interpolation
   plain = "plain text";
 }

tests/uri_test.nix

@@ -0,0 +1,3 @@
+https://example.com/path?query=1
+#frag
+