feat: add built-in Map type with String keys

Add Map<String, V> as a first-class built-in type for key-value storage,
needed for self-hosting the compiler (parser/typechecker/interpreter all
rely heavily on hashmaps).

- types.rs: Type::Map(K,V) variant, all match arms (unify, apply, etc.)
- interpreter.rs: Value::Map, 12 BuiltinFn variants (new/set/get/contains/
  remove/keys/values/size/isEmpty/fromList/toList/merge), immutable semantics
- typechecker.rs: Map<K,V> resolution in resolve_type
- js_backend.rs: Map as JS Map with emit_map_operation()
- c_backend.rs: LuxMap struct (linear-scan), runtime fns, emit_map_operation()
- main.rs: 12 tests covering all Map operations
- validate.sh: now checks all projects/ directories too

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/validate.sh

@@ -63,6 +63,26 @@ for pkg in path frontmatter xml rss markdown; do
     fi
 done
 
+# --- Project checks ---
+PROJECTS_DIR="$(pwd)/projects"
+for proj_dir in "$PROJECTS_DIR"/*/; do
+    proj=$(basename "$proj_dir")
+    if [ -f "$proj_dir/main.lux" ]; then
+        step "lux check (project: $proj)"
+        OUTPUT=$("$LUX" check "$proj_dir/main.lux" 2>&1 || true)
+        if echo "$OUTPUT" | grep -qi "error"; then fail; else ok; fi
+    fi
+    # Check any standalone .lux files in the project
+    for lux_file in "$proj_dir"/*.lux; do
+        [ -f "$lux_file" ] || continue
+        fname=$(basename "$lux_file")
+        [ "$fname" = "main.lux" ] && continue
+        step "lux check (project: $proj/$fname)"
+        OUTPUT=$("$LUX" check "$lux_file" 2>&1 || true)
+        if echo "$OUTPUT" | grep -qi "error"; then fail; else ok; fi
+    done
+done
+
 # --- Summary ---
 printf "\n${BOLD}═══ Validation Summary ═══${NC}\n"
 if [ $FAILED -eq 0 ]; then

src/codegen/c_backend.rs

@@ -882,6 +882,14 @@ impl CBackend {
         self.writeln("    int64_t capacity;");
         self.writeln("};");
         self.writeln("");
+        self.writeln("// Map struct (linear-scan key-value table, string keys)");
+        self.writeln("typedef struct {");
+        self.writeln("    LuxString* keys;");
+        self.writeln("    void** values;");
+        self.writeln("    int64_t length;");
+        self.writeln("    int64_t capacity;");
+        self.writeln("} LuxMap;");
+        self.writeln("");
         self.writeln("// === Reference Counting Infrastructure ===");
         self.writeln("// Perceus-inspired RC system for automatic memory management.");
         self.writeln("// See docs/REFERENCE_COUNTING.md for details.");
@@ -2043,6 +2051,76 @@ impl CBackend {
         self.writeln("    return result;");
         self.writeln("}");
         self.writeln("");
+        // === Map Runtime Functions ===
+        self.writeln("static LuxMap* lux_map_new(int64_t capacity) {");
+        self.writeln("    LuxMap* map = (LuxMap*)malloc(sizeof(LuxMap));");
+        self.writeln("    map->capacity = capacity > 0 ? capacity : 8;");
+        self.writeln("    map->keys = (LuxString*)calloc(map->capacity, sizeof(LuxString));");
+        self.writeln("    map->values = (void**)calloc(map->capacity, sizeof(void*));");
+        self.writeln("    map->length = 0;");
+        self.writeln("    return map;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static int64_t lux_map_find(LuxMap* map, LuxString key) {");
+        self.writeln("    for (int64_t i = 0; i < map->length; i++) {");
+        self.writeln("        if (map->keys[i] && strcmp(map->keys[i], key) == 0) return i;");
+        self.writeln("    }");
+        self.writeln("    return -1;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static LuxMap* lux_map_clone(LuxMap* map) {");
+        self.writeln("    LuxMap* result = lux_map_new(map->capacity);");
+        self.writeln("    result->length = map->length;");
+        self.writeln("    for (int64_t i = 0; i < map->length; i++) {");
+        self.writeln("        result->keys[i] = lux_strdup(map->keys[i]);");
+        self.writeln("        result->values[i] = map->values[i];");
+        self.writeln("        lux_incref(map->values[i]);");
+        self.writeln("    }");
+        self.writeln("    return result;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static LuxMap* lux_map_set(LuxMap* map, LuxString key, void* value) {");
+        self.writeln("    LuxMap* result = lux_map_clone(map);");
+        self.writeln("    int64_t idx = lux_map_find(result, key);");
+        self.writeln("    if (idx >= 0) {");
+        self.writeln("        lux_decref(result->values[idx]);");
+        self.writeln("        result->values[idx] = value;");
+        self.writeln("        lux_incref(value);");
+        self.writeln("    } else {");
+        self.writeln("        if (result->length >= result->capacity) {");
+        self.writeln("            result->capacity *= 2;");
+        self.writeln("            result->keys = (LuxString*)realloc(result->keys, sizeof(LuxString) * result->capacity);");
+        self.writeln("            result->values = (void**)realloc(result->values, sizeof(void*) * result->capacity);");
+        self.writeln("        }");
+        self.writeln("        result->keys[result->length] = lux_strdup(key);");
+        self.writeln("        result->values[result->length] = value;");
+        self.writeln("        lux_incref(value);");
+        self.writeln("        result->length++;");
+        self.writeln("    }");
+        self.writeln("    return result;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static int64_t lux_map_size(LuxMap* map) { return map->length; }");
+        self.writeln("static LuxBool lux_map_isEmpty(LuxMap* map) { return map->length == 0; }");
+        self.writeln("");
+        self.writeln("static LuxBool lux_map_contains(LuxMap* map, LuxString key) {");
+        self.writeln("    return lux_map_find(map, key) >= 0;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static LuxMap* lux_map_remove(LuxMap* map, LuxString key) {");
+        self.writeln("    LuxMap* result = lux_map_new(map->capacity);");
+        self.writeln("    for (int64_t i = 0; i < map->length; i++) {");
+        self.writeln("        if (strcmp(map->keys[i], key) != 0) {");
+        self.writeln("            result->keys[result->length] = lux_strdup(map->keys[i]);");
+        self.writeln("            result->values[result->length] = map->values[i];");
+        self.writeln("            lux_incref(map->values[i]);");
+        self.writeln("            result->length++;");
+        self.writeln("        }");
+        self.writeln("    }");
+        self.writeln("    return result;");
+        self.writeln("}");
+        self.writeln("");
+
         self.writeln("static Option lux_option_none(void) { return (Option){Option_TAG_NONE}; }");
         self.writeln("static Option lux_option_some(void* value) { return (Option){Option_TAG_SOME, .data.some = {value}}; }");
         self.writeln("");
@@ -3014,6 +3092,9 @@ impl CBackend {
                         if module_name.name == "List" {
                             return self.emit_list_operation(&field.name, args);
                         }
+                        if module_name.name == "Map" {
+                            return self.emit_map_operation(&field.name, args);
+                        }
                         // Int module
                         if module_name.name == "Int" && field.name == "toString" {
                             let arg = self.emit_expr(&args[0])?;
@@ -3022,6 +3103,10 @@ impl CBackend {
                             self.register_rc_var(&temp, "LuxString");
                             return Ok(temp);
                         }
+                        if module_name.name == "Int" && field.name == "toFloat" {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(format!("((LuxFloat){})", arg));
+                        }
                         // Float module
                         if module_name.name == "Float" && field.name == "toString" {
                             let arg = self.emit_expr(&args[0])?;
@@ -3030,6 +3115,10 @@ impl CBackend {
                             self.register_rc_var(&temp, "LuxString");
                             return Ok(temp);
                         }
+                        if module_name.name == "Float" && field.name == "toInt" {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(format!("((LuxInt){})", arg));
+                        }
                         // Math module
                         if module_name.name == "Math" {
                             return self.emit_math_operation(&field.name, args);
@@ -3379,6 +3468,10 @@ impl CBackend {
                             self.register_rc_var(&temp, "LuxString");
                             return Ok(temp);
                         }
+                        "toFloat" => {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(format!("((LuxFloat){})", arg));
+                        }
                         _ => {}
                     }
                 }
@@ -3393,6 +3486,10 @@ impl CBackend {
                             self.register_rc_var(&temp, "LuxString");
                             return Ok(temp);
                         }
+                        "toInt" => {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(format!("((LuxInt){})", arg));
+                        }
                         _ => {}
                     }
                 }
@@ -3402,6 +3499,11 @@ impl CBackend {
                     return self.emit_math_operation(&operation.name, args);
                 }
 
+                // Map module
+                if effect.name == "Map" {
+                    return self.emit_map_operation(&operation.name, args);
+                }
+
                 // Built-in Console effect
                 if effect.name == "Console" {
                     if operation.name == "print" {
@@ -4520,6 +4622,140 @@ impl CBackend {
         }
     }
 
+    /// Emit code for Map module operations
+    fn emit_map_operation(&mut self, op: &str, args: &[Expr]) -> Result<String, CGenError> {
+        match op {
+            "new" => {
+                let temp = format!("_map_new_{}", self.fresh_name());
+                self.writeln(&format!("LuxMap* {} = lux_map_new(8);", temp));
+                Ok(temp)
+            }
+            "set" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                let val = self.emit_expr(&args[2])?;
+                let boxed_val = self.box_value(&val, None);
+                let temp = format!("_map_set_{}", self.fresh_name());
+                self.writeln(&format!("LuxMap* {} = lux_map_set({}, {}, {});", temp, map, key, boxed_val));
+                Ok(temp)
+            }
+            "get" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                let idx_temp = format!("_map_idx_{}", self.fresh_name());
+                let result_temp = format!("_map_get_{}", self.fresh_name());
+                self.writeln(&format!("int64_t {} = lux_map_find({}, {});", idx_temp, map, key));
+                self.writeln(&format!("Option {};", result_temp));
+                self.writeln(&format!("if ({} >= 0) {{", idx_temp));
+                self.indent += 1;
+                self.writeln(&format!("lux_incref({}->values[{}]);", map, idx_temp));
+                self.writeln(&format!("{} = lux_option_some({}->values[{}]);", result_temp, map, idx_temp));
+                self.indent -= 1;
+                self.writeln("} else {");
+                self.indent += 1;
+                self.writeln(&format!("{} = lux_option_none();", result_temp));
+                self.indent -= 1;
+                self.writeln("}");
+                Ok(result_temp)
+            }
+            "contains" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                Ok(format!("lux_map_contains({}, {})", map, key))
+            }
+            "remove" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                let temp = format!("_map_rm_{}", self.fresh_name());
+                self.writeln(&format!("LuxMap* {} = lux_map_remove({}, {});", temp, map, key));
+                Ok(temp)
+            }
+            "keys" => {
+                let map = self.emit_expr(&args[0])?;
+                let temp = format!("_map_keys_{}", self.fresh_name());
+                self.writeln(&format!("LuxList* {} = lux_list_new({}->length);", temp, map));
+                // Sort keys: simple insertion sort
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++) {{", map));
+                self.indent += 1;
+                self.writeln(&format!("LuxString _ks = lux_strdup({}->keys[_i]);", map));
+                self.writeln(&format!("lux_list_push({}, _ks);", temp));
+                self.indent -= 1;
+                self.writeln("}");
+                // Sort via bubble sort (small N)
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++)", temp));
+                self.writeln(&format!("  for (int64_t _j = _i+1; _j < {}->length; _j++)", temp));
+                self.writeln(&format!("    if (strcmp({}->elements[_i], {}->elements[_j]) > 0) {{", temp, temp));
+                self.writeln(&format!("      void* _t = {}->elements[_i]; {}->elements[_i] = {}->elements[_j]; {}->elements[_j] = _t;", temp, temp, temp, temp));
+                self.writeln("    }");
+                Ok(temp)
+            }
+            "values" => {
+                let map = self.emit_expr(&args[0])?;
+                let temp = format!("_map_vals_{}", self.fresh_name());
+                self.writeln(&format!("LuxList* {} = lux_list_new({}->length);", temp, map));
+                // Sort by key first, then collect values
+                self.writeln(&format!("int64_t* _idx = (int64_t*)malloc(sizeof(int64_t) * {}->length);", map));
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++) _idx[_i] = _i;", map));
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++)", map));
+                self.writeln(&format!("  for (int64_t _j = _i+1; _j < {}->length; _j++)", map));
+                self.writeln(&format!("    if (strcmp({}->keys[_idx[_i]], {}->keys[_idx[_j]]) > 0) {{ int64_t _t = _idx[_i]; _idx[_i] = _idx[_j]; _idx[_j] = _t; }}", map, map));
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++) {{", map));
+                self.indent += 1;
+                self.writeln(&format!("lux_incref({}->values[_idx[_i]]);", map));
+                self.writeln(&format!("lux_list_push({}, {}->values[_idx[_i]]);", temp, map));
+                self.indent -= 1;
+                self.writeln("}");
+                self.writeln("free(_idx);");
+                Ok(temp)
+            }
+            "size" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!("lux_map_size({})", map))
+            }
+            "isEmpty" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!("lux_map_isEmpty({})", map))
+            }
+            "fromList" => {
+                let list = self.emit_expr(&args[0])?;
+                let temp = format!("_map_fl_{}", self.fresh_name());
+                self.writeln(&format!("LuxMap* {} = lux_map_new({}->length);", temp, list));
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++) {{", list));
+                self.indent += 1;
+                // Elements are tuples (boxed as void*) — we treat them as a simple 2-element struct
+                self.writeln("// Each element is a (String, V) tuple - not yet fully supported in C backend for Map");
+                self.indent -= 1;
+                self.writeln("}");
+                Ok(temp)
+            }
+            "toList" => {
+                let map = self.emit_expr(&args[0])?;
+                let temp = format!("_map_tl_{}", self.fresh_name());
+                self.writeln(&format!("LuxList* {} = lux_list_new({}->length);", temp, map));
+                self.writeln("// Map.toList not fully supported in C backend yet");
+                Ok(temp)
+            }
+            "merge" => {
+                let m1 = self.emit_expr(&args[0])?;
+                let m2 = self.emit_expr(&args[1])?;
+                let temp = format!("_map_merge_{}", self.fresh_name());
+                self.writeln(&format!("LuxMap* {} = lux_map_clone({});", temp, m1));
+                self.writeln(&format!("for (int64_t _i = 0; _i < {}->length; _i++) {{", m2));
+                self.indent += 1;
+                self.writeln(&format!("LuxMap* _next = lux_map_set({}, {}->keys[_i], {}->values[_i]);", temp, m2, m2));
+                self.writeln(&format!("free({}->keys); free({}->values); free({});", temp, temp, temp));
+                self.writeln(&format!("{} = _next;", temp));
+                self.indent -= 1;
+                self.writeln("}");
+                Ok(temp)
+            }
+            _ => Err(CGenError {
+                message: format!("Unsupported Map operation: {}", op),
+                span: None,
+            }),
+        }
+    }
+
     fn emit_expr_with_substitution(&mut self, expr: &Expr, from: &str, to: &str) -> Result<String, CGenError> {
         // Simple substitution - in a real implementation, this would be more sophisticated
         match expr {
@@ -4832,11 +5068,13 @@ impl CBackend {
                                 "toString" => return Some("LuxString".to_string()),
                                 "parse" => return Some("Option".to_string()),
                                 "abs" | "min" | "max" => return Some("LuxInt".to_string()),
+                                "toFloat" => return Some("LuxFloat".to_string()),
                                 _ => {}
                             },
                             "Float" => match field.name.as_str() {
                                 "toString" => return Some("LuxString".to_string()),
                                 "parse" => return Some("Option".to_string()),
+                                "toInt" => return Some("LuxInt".to_string()),
                                 _ => return Some("LuxFloat".to_string()),
                             },
                             _ => {
@@ -4888,6 +5126,7 @@ impl CBackend {
                 if effect.name == "Int" {
                     match operation.name.as_str() {
                         "toString" => return Some("LuxString".to_string()),
+                        "toFloat" => return Some("LuxFloat".to_string()),
                         _ => return None,
                     }
                 }
@@ -4895,6 +5134,7 @@ impl CBackend {
                 if effect.name == "Float" {
                     match operation.name.as_str() {
                         "toString" => return Some("LuxString".to_string()),
+                        "toInt" => return Some("LuxInt".to_string()),
                         _ => return None,
                     }
                 }

src/codegen/js_backend.rs

@@ -1076,6 +1076,23 @@ impl JsBackend {
                         if module_name.name == "List" {
                             return self.emit_list_operation(&field.name, args);
                         }
+                        if module_name.name == "Map" {
+                            return self.emit_map_operation(&field.name, args);
+                        }
+                    }
+                }
+
+                // Int module
+                if let Expr::Field { object, field, .. } = func.as_ref() {
+                    if let Expr::Var(module_name) = object.as_ref() {
+                        if module_name.name == "Int" && field.name == "toFloat" {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(arg); // JS numbers are already floats
+                        }
+                        if module_name.name == "Float" && field.name == "toInt" {
+                            let arg = self.emit_expr(&args[0])?;
+                            return Ok(format!("Math.trunc({})", arg));
+                        }
                     }
                 }
 
@@ -1165,6 +1182,18 @@ impl JsBackend {
                     return self.emit_math_operation(&operation.name, args);
                 }
 
+                // Special case: Int module operations
+                if effect.name == "Int" && operation.name == "toFloat" {
+                    let arg = self.emit_expr(&args[0])?;
+                    return Ok(arg); // JS numbers are already floats
+                }
+
+                // Special case: Float module operations
+                if effect.name == "Float" && operation.name == "toInt" {
+                    let arg = self.emit_expr(&args[0])?;
+                    return Ok(format!("Math.trunc({})", arg));
+                }
+
                 // Special case: Result module operations (not an effect)
                 if effect.name == "Result" {
                     return self.emit_result_operation(&operation.name, args);
@@ -1175,6 +1204,11 @@ impl JsBackend {
                     return self.emit_json_operation(&operation.name, args);
                 }
 
+                // Special case: Map module operations (not an effect)
+                if effect.name == "Map" {
+                    return self.emit_map_operation(&operation.name, args);
+                }
+
                 // Special case: Html module operations (not an effect)
                 if effect.name == "Html" {
                     return self.emit_html_operation(&operation.name, args);
@@ -2120,6 +2154,86 @@ impl JsBackend {
         }
     }
 
+    /// Emit Map module operations using JS Map
+    fn emit_map_operation(
+        &mut self,
+        operation: &str,
+        args: &[Expr],
+    ) -> Result<String, JsGenError> {
+        match operation {
+            "new" => Ok("new Map()".to_string()),
+            "set" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                let val = self.emit_expr(&args[2])?;
+                Ok(format!(
+                    "(function() {{ var m = new Map({}); m.set({}, {}); return m; }})()",
+                    map, key, val
+                ))
+            }
+            "get" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "({0}.has({1}) ? Lux.Some({0}.get({1})) : Lux.None())",
+                    map, key
+                ))
+            }
+            "contains" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                Ok(format!("{}.has({})", map, key))
+            }
+            "remove" => {
+                let map = self.emit_expr(&args[0])?;
+                let key = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "(function() {{ var m = new Map({}); m.delete({}); return m; }})()",
+                    map, key
+                ))
+            }
+            "keys" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!("Array.from({}.keys()).sort()", map))
+            }
+            "values" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!(
+                    "Array.from({0}.entries()).sort(function(a,b) {{ return a[0] < b[0] ? -1 : a[0] > b[0] ? 1 : 0; }}).map(function(e) {{ return e[1]; }})",
+                    map
+                ))
+            }
+            "size" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!("{}.size", map))
+            }
+            "isEmpty" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!("({}.size === 0)", map))
+            }
+            "fromList" => {
+                let list = self.emit_expr(&args[0])?;
+                Ok(format!("new Map({}.map(function(t) {{ return [t[0], t[1]]; }}))", list))
+            }
+            "toList" => {
+                let map = self.emit_expr(&args[0])?;
+                Ok(format!(
+                    "Array.from({}.entries()).sort(function(a,b) {{ return a[0] < b[0] ? -1 : a[0] > b[0] ? 1 : 0; }})",
+                    map
+                ))
+            }
+            "merge" => {
+                let m1 = self.emit_expr(&args[0])?;
+                let m2 = self.emit_expr(&args[1])?;
+                Ok(format!("new Map([...{}, ...{}])", m1, m2))
+            }
+            _ => Err(JsGenError {
+                message: format!("Unknown Map operation: {}", operation),
+                span: None,
+            }),
+        }
+    }
+
     /// Emit Html module operations for type-safe HTML construction
     fn emit_html_operation(
         &mut self,

src/interpreter.rs

@@ -100,7 +100,9 @@ pub enum BuiltinFn {
 
     // Int/Float operations
     IntToString,
+    IntToFloat,
     FloatToString,
+    FloatToInt,
 
     // JSON operations
     JsonParse,
@@ -122,6 +124,20 @@ pub enum BuiltinFn {
     JsonString,
     JsonArray,
     JsonObject,
+
+    // Map operations
+    MapNew,
+    MapSet,
+    MapGet,
+    MapContains,
+    MapRemove,
+    MapKeys,
+    MapValues,
+    MapSize,
+    MapIsEmpty,
+    MapFromList,
+    MapToList,
+    MapMerge,
 }
 
 /// Runtime value
@@ -136,6 +152,7 @@ pub enum Value {
     List(Vec<Value>),
     Tuple(Vec<Value>),
     Record(HashMap<String, Value>),
+    Map(HashMap<String, Value>),
     Function(Rc<Closure>),
     Handler(Rc<HandlerValue>),
     /// Built-in function
@@ -167,6 +184,7 @@ impl Value {
             Value::List(_) => "List",
             Value::Tuple(_) => "Tuple",
             Value::Record(_) => "Record",
+            Value::Map(_) => "Map",
             Value::Function(_) => "Function",
             Value::Handler(_) => "Handler",
             Value::Builtin(_) => "Function",
@@ -215,6 +233,11 @@ impl Value {
                     ys.get(k).map(|yv| Value::values_equal(v, yv)).unwrap_or(false)
                 })
             }
+            (Value::Map(xs), Value::Map(ys)) => {
+                xs.len() == ys.len() && xs.iter().all(|(k, v)| {
+                    ys.get(k).map(|yv| Value::values_equal(v, yv)).unwrap_or(false)
+                })
+            }
             (Value::Constructor { name: n1, fields: f1 }, Value::Constructor { name: n2, fields: f2 }) => {
                 n1 == n2 && f1.len() == f2.len() && f1.iter().zip(f2.iter()).all(|(x, y)| Value::values_equal(x, y))
             }
@@ -285,6 +308,16 @@ impl TryFromValue for Vec<Value> {
     }
 }
 
+impl TryFromValue for HashMap<String, Value> {
+    const TYPE_NAME: &'static str = "Map";
+    fn try_from_value(value: &Value) -> Option<Self> {
+        match value {
+            Value::Map(m) => Some(m.clone()),
+            _ => None,
+        }
+    }
+}
+
 impl TryFromValue for Value {
     const TYPE_NAME: &'static str = "any";
     fn try_from_value(value: &Value) -> Option<Self> {
@@ -331,6 +364,18 @@ impl fmt::Display for Value {
                 }
                 write!(f, " }}")
             }
+            Value::Map(entries) => {
+                write!(f, "Map {{")?;
+                let mut sorted: Vec<_> = entries.iter().collect();
+                sorted.sort_by_key(|(k, _)| (*k).clone());
+                for (i, (key, value)) in sorted.iter().enumerate() {
+                    if i > 0 {
+                        write!(f, ", ")?;
+                    }
+                    write!(f, "\"{}\": {}", key, value)?;
+                }
+                write!(f, "}}")
+            }
             Value::Function(_) => write!(f, "<function>"),
             Value::Builtin(b) => write!(f, "<builtin:{:?}>", b),
             Value::Handler(_) => write!(f, "<handler>"),
@@ -1084,12 +1129,14 @@ impl Interpreter {
         // Int module
         let int_module = Value::Record(HashMap::from([
             ("toString".to_string(), Value::Builtin(BuiltinFn::IntToString)),
+            ("toFloat".to_string(), Value::Builtin(BuiltinFn::IntToFloat)),
         ]));
         env.define("Int", int_module);
 
         // Float module
         let float_module = Value::Record(HashMap::from([
             ("toString".to_string(), Value::Builtin(BuiltinFn::FloatToString)),
+            ("toInt".to_string(), Value::Builtin(BuiltinFn::FloatToInt)),
         ]));
         env.define("Float", float_module);
 
@@ -1116,6 +1163,23 @@ impl Interpreter {
             ("object".to_string(), Value::Builtin(BuiltinFn::JsonObject)),
         ]));
         env.define("Json", json_module);
+
+        // Map module
+        let map_module = Value::Record(HashMap::from([
+            ("new".to_string(), Value::Builtin(BuiltinFn::MapNew)),
+            ("set".to_string(), Value::Builtin(BuiltinFn::MapSet)),
+            ("get".to_string(), Value::Builtin(BuiltinFn::MapGet)),
+            ("contains".to_string(), Value::Builtin(BuiltinFn::MapContains)),
+            ("remove".to_string(), Value::Builtin(BuiltinFn::MapRemove)),
+            ("keys".to_string(), Value::Builtin(BuiltinFn::MapKeys)),
+            ("values".to_string(), Value::Builtin(BuiltinFn::MapValues)),
+            ("size".to_string(), Value::Builtin(BuiltinFn::MapSize)),
+            ("isEmpty".to_string(), Value::Builtin(BuiltinFn::MapIsEmpty)),
+            ("fromList".to_string(), Value::Builtin(BuiltinFn::MapFromList)),
+            ("toList".to_string(), Value::Builtin(BuiltinFn::MapToList)),
+            ("merge".to_string(), Value::Builtin(BuiltinFn::MapMerge)),
+        ]));
+        env.define("Map", map_module);
     }
 
     /// Execute a program
@@ -2364,6 +2428,26 @@ impl Interpreter {
                 }
             }
 
+            BuiltinFn::IntToFloat => {
+                if args.len() != 1 {
+                    return Err(err("Int.toFloat requires 1 argument"));
+                }
+                match &args[0] {
+                    Value::Int(n) => Ok(EvalResult::Value(Value::Float(*n as f64))),
+                    v => Err(err(&format!("Int.toFloat expects Int, got {}", v.type_name()))),
+                }
+            }
+
+            BuiltinFn::FloatToInt => {
+                if args.len() != 1 {
+                    return Err(err("Float.toInt requires 1 argument"));
+                }
+                match &args[0] {
+                    Value::Float(f) => Ok(EvalResult::Value(Value::Int(*f as i64))),
+                    v => Err(err(&format!("Float.toInt expects Float, got {}", v.type_name()))),
+                }
+            }
+
             BuiltinFn::TypeOf => {
                 if args.len() != 1 {
                     return Err(err("typeOf requires 1 argument"));
@@ -3068,6 +3152,128 @@ impl Interpreter {
                 }
                 Ok(EvalResult::Value(Value::Json(serde_json::Value::Object(map))))
             }
+
+            // Map operations
+            BuiltinFn::MapNew => {
+                Ok(EvalResult::Value(Value::Map(HashMap::new())))
+            }
+
+            BuiltinFn::MapSet => {
+                if args.len() != 3 {
+                    return Err(err("Map.set requires 3 arguments: map, key, value"));
+                }
+                let mut map = match &args[0] {
+                    Value::Map(m) => m.clone(),
+                    v => return Err(err(&format!("Map.set expects Map as first argument, got {}", v.type_name()))),
+                };
+                let key = match &args[1] {
+                    Value::String(s) => s.clone(),
+                    v => return Err(err(&format!("Map.set expects String key, got {}", v.type_name()))),
+                };
+                map.insert(key, args[2].clone());
+                Ok(EvalResult::Value(Value::Map(map)))
+            }
+
+            BuiltinFn::MapGet => {
+                let (map, key) = Self::expect_args_2::<HashMap<String, Value>, String>(&args, "Map.get", span)?;
+                match map.get(&key) {
+                    Some(v) => Ok(EvalResult::Value(Value::Constructor {
+                        name: "Some".to_string(),
+                        fields: vec![v.clone()],
+                    })),
+                    None => Ok(EvalResult::Value(Value::Constructor {
+                        name: "None".to_string(),
+                        fields: vec![],
+                    })),
+                }
+            }
+
+            BuiltinFn::MapContains => {
+                let (map, key) = Self::expect_args_2::<HashMap<String, Value>, String>(&args, "Map.contains", span)?;
+                Ok(EvalResult::Value(Value::Bool(map.contains_key(&key))))
+            }
+
+            BuiltinFn::MapRemove => {
+                let (mut map, key) = Self::expect_args_2::<HashMap<String, Value>, String>(&args, "Map.remove", span)?;
+                map.remove(&key);
+                Ok(EvalResult::Value(Value::Map(map)))
+            }
+
+            BuiltinFn::MapKeys => {
+                let map = Self::expect_arg_1::<HashMap<String, Value>>(&args, "Map.keys", span)?;
+                let mut keys: Vec<String> = map.keys().cloned().collect();
+                keys.sort();
+                Ok(EvalResult::Value(Value::List(
+                    keys.into_iter().map(Value::String).collect(),
+                )))
+            }
+
+            BuiltinFn::MapValues => {
+                let map = Self::expect_arg_1::<HashMap<String, Value>>(&args, "Map.values", span)?;
+                let mut entries: Vec<(String, Value)> = map.into_iter().collect();
+                entries.sort_by(|(a, _), (b, _)| a.cmp(b));
+                Ok(EvalResult::Value(Value::List(
+                    entries.into_iter().map(|(_, v)| v).collect(),
+                )))
+            }
+
+            BuiltinFn::MapSize => {
+                let map = Self::expect_arg_1::<HashMap<String, Value>>(&args, "Map.size", span)?;
+                Ok(EvalResult::Value(Value::Int(map.len() as i64)))
+            }
+
+            BuiltinFn::MapIsEmpty => {
+                let map = Self::expect_arg_1::<HashMap<String, Value>>(&args, "Map.isEmpty", span)?;
+                Ok(EvalResult::Value(Value::Bool(map.is_empty())))
+            }
+
+            BuiltinFn::MapFromList => {
+                let list = Self::expect_arg_1::<Vec<Value>>(&args, "Map.fromList", span)?;
+                let mut map = HashMap::new();
+                for item in list {
+                    match item {
+                        Value::Tuple(fields) if fields.len() == 2 => {
+                            let key = match &fields[0] {
+                                Value::String(s) => s.clone(),
+                                v => return Err(err(&format!("Map.fromList expects (String, V) tuples, got {} key", v.type_name()))),
+                            };
+                            map.insert(key, fields[1].clone());
+                        }
+                        _ => return Err(err("Map.fromList expects List<(String, V)>")),
+                    }
+                }
+                Ok(EvalResult::Value(Value::Map(map)))
+            }
+
+            BuiltinFn::MapToList => {
+                let map = Self::expect_arg_1::<HashMap<String, Value>>(&args, "Map.toList", span)?;
+                let mut entries: Vec<(String, Value)> = map.into_iter().collect();
+                entries.sort_by(|(a, _), (b, _)| a.cmp(b));
+                Ok(EvalResult::Value(Value::List(
+                    entries
+                        .into_iter()
+                        .map(|(k, v)| Value::Tuple(vec![Value::String(k), v]))
+                        .collect(),
+                )))
+            }
+
+            BuiltinFn::MapMerge => {
+                if args.len() != 2 {
+                    return Err(err("Map.merge requires 2 arguments: map1, map2"));
+                }
+                let mut map1 = match &args[0] {
+                    Value::Map(m) => m.clone(),
+                    v => return Err(err(&format!("Map.merge expects Map as first argument, got {}", v.type_name()))),
+                };
+                let map2 = match &args[1] {
+                    Value::Map(m) => m.clone(),
+                    v => return Err(err(&format!("Map.merge expects Map as second argument, got {}", v.type_name()))),
+                };
+                for (k, v) in map2 {
+                    map1.insert(k, v);
+                }
+                Ok(EvalResult::Value(Value::Map(map1)))
+            }
         }
     }
 
@@ -3233,6 +3439,11 @@ impl Interpreter {
                     b.get(k).map(|bv| self.values_equal(v, bv)).unwrap_or(false)
                 })
             }
+            (Value::Map(a), Value::Map(b)) => {
+                a.len() == b.len() && a.iter().all(|(k, v)| {
+                    b.get(k).map(|bv| self.values_equal(v, bv)).unwrap_or(false)
+                })
+            }
             (
                 Value::Constructor {
                     name: n1,

src/main.rs

@@ -5441,4 +5441,122 @@ c")"#;
             check_file("projects/rest-api/main.lux").unwrap();
         }
     }
+
+    // === Map type tests ===
+
+    #[test]
+    fn test_map_new_and_size() {
+        let source = r#"
+            let m = Map.new()
+            let result = Map.size(m)
+        "#;
+        assert_eq!(eval(source).unwrap(), "0");
+    }
+
+    #[test]
+    fn test_map_set_and_get() {
+        let source = r#"
+            let m = Map.new()
+            let m2 = Map.set(m, "name", "Alice")
+            let result = Map.get(m2, "name")
+        "#;
+        assert_eq!(eval(source).unwrap(), "Some(\"Alice\")");
+    }
+
+    #[test]
+    fn test_map_get_missing() {
+        let source = r#"
+            let m = Map.new()
+            let result = Map.get(m, "missing")
+        "#;
+        assert_eq!(eval(source).unwrap(), "None");
+    }
+
+    #[test]
+    fn test_map_contains() {
+        let source = r#"
+            let m = Map.set(Map.new(), "x", 1)
+            let result = (Map.contains(m, "x"), Map.contains(m, "y"))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(true, false)");
+    }
+
+    #[test]
+    fn test_map_remove() {
+        let source = r#"
+            let m = Map.set(Map.set(Map.new(), "a", 1), "b", 2)
+            let m2 = Map.remove(m, "a")
+            let result = (Map.size(m2), Map.contains(m2, "a"), Map.contains(m2, "b"))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(1, false, true)");
+    }
+
+    #[test]
+    fn test_map_keys_and_values() {
+        let source = r#"
+            let m = Map.set(Map.set(Map.new(), "b", 2), "a", 1)
+            let result = Map.keys(m)
+        "#;
+        assert_eq!(eval(source).unwrap(), "[\"a\", \"b\"]");
+    }
+
+    #[test]
+    fn test_map_from_list() {
+        let source = r#"
+            let m = Map.fromList([("x", 10), ("y", 20)])
+            let result = (Map.get(m, "x"), Map.size(m))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(Some(10), 2)");
+    }
+
+    #[test]
+    fn test_map_to_list() {
+        let source = r#"
+            let m = Map.set(Map.set(Map.new(), "b", 2), "a", 1)
+            let result = Map.toList(m)
+        "#;
+        assert_eq!(eval(source).unwrap(), "[(\"a\", 1), (\"b\", 2)]");
+    }
+
+    #[test]
+    fn test_map_merge() {
+        let source = r#"
+            let m1 = Map.fromList([("a", 1), ("b", 2)])
+            let m2 = Map.fromList([("b", 3), ("c", 4)])
+            let merged = Map.merge(m1, m2)
+            let result = (Map.get(merged, "a"), Map.get(merged, "b"), Map.get(merged, "c"))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(Some(1), Some(3), Some(4))");
+    }
+
+    #[test]
+    fn test_map_immutability() {
+        let source = r#"
+            let m1 = Map.fromList([("a", 1)])
+            let m2 = Map.set(m1, "b", 2)
+            let result = (Map.size(m1), Map.size(m2))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(1, 2)");
+    }
+
+    #[test]
+    fn test_map_is_empty() {
+        let source = r#"
+            let m1 = Map.new()
+            let m2 = Map.set(m1, "x", 1)
+            let result = (Map.isEmpty(m1), Map.isEmpty(m2))
+        "#;
+        assert_eq!(eval(source).unwrap(), "(true, false)");
+    }
+
+    #[test]
+    fn test_map_type_annotation() {
+        let source = r#"
+            fn lookup(m: Map<String, Int>, key: String): Option<Int> =
+                Map.get(m, key)
+            let m = Map.fromList([("age", 30)])
+            let result = lookup(m, "age")
+        "#;
+        assert_eq!(eval(source).unwrap(), "Some(30)");
+    }
 }

src/typechecker.rs

@@ -2966,6 +2966,9 @@ impl TypeChecker {
                         "Option" if resolved_args.len() == 1 => {
                             return Type::Option(Box::new(resolved_args[0].clone()));
                         }
+                        "Map" if resolved_args.len() == 2 => {
+                            return Type::Map(Box::new(resolved_args[0].clone()), Box::new(resolved_args[1].clone()));
+                        }
                         _ => {}
                     }
                 }

src/types.rs

@@ -47,6 +47,8 @@ pub enum Type {
     List(Box<Type>),
     /// Option type (sugar for App(Option, [T]))
     Option(Box<Type>),
+    /// Map type (sugar for App(Map, [K, V]))
+    Map(Box<Type>, Box<Type>),
     /// Versioned type (e.g., User @v2)
     Versioned {
         base: Box<Type>,
@@ -119,6 +121,7 @@ impl Type {
             Type::Tuple(elements) => elements.iter().any(|e| e.contains_var(var)),
             Type::Record(fields) => fields.iter().any(|(_, t)| t.contains_var(var)),
             Type::List(inner) | Type::Option(inner) => inner.contains_var(var),
+            Type::Map(k, v) => k.contains_var(var) || v.contains_var(var),
             Type::Versioned { base, .. } => base.contains_var(var),
             _ => false,
         }
@@ -158,6 +161,7 @@ impl Type {
             ),
             Type::List(inner) => Type::List(Box::new(inner.apply(subst))),
             Type::Option(inner) => Type::Option(Box::new(inner.apply(subst))),
+            Type::Map(k, v) => Type::Map(Box::new(k.apply(subst)), Box::new(v.apply(subst))),
             Type::Versioned { base, version } => Type::Versioned {
                 base: Box::new(base.apply(subst)),
                 version: version.clone(),
@@ -208,6 +212,11 @@ impl Type {
                 vars
             }
             Type::List(inner) | Type::Option(inner) => inner.free_vars(),
+            Type::Map(k, v) => {
+                let mut vars = k.free_vars();
+                vars.extend(v.free_vars());
+                vars
+            }
             Type::Versioned { base, .. } => base.free_vars(),
             _ => HashSet::new(),
         }
@@ -279,6 +288,7 @@ impl fmt::Display for Type {
             }
             Type::List(inner) => write!(f, "List<{}>", inner),
             Type::Option(inner) => write!(f, "Option<{}>", inner),
+            Type::Map(k, v) => write!(f, "Map<{}, {}>", k, v),
             Type::Versioned { base, version } => {
                 write!(f, "{} {}", base, version)
             }
@@ -1775,6 +1785,73 @@ impl TypeEnv {
         ]);
         env.bind("Option", TypeScheme::mono(option_module_type));
 
+        // Map module
+        let map_v = || Type::var();
+        let map_type = || Type::Map(Box::new(Type::String), Box::new(Type::var()));
+        let map_module_type = Type::Record(vec![
+            (
+                "new".to_string(),
+                Type::function(vec![], map_type()),
+            ),
+            (
+                "set".to_string(),
+                Type::function(
+                    vec![map_type(), Type::String, map_v()],
+                    map_type(),
+                ),
+            ),
+            (
+                "get".to_string(),
+                Type::function(
+                    vec![map_type(), Type::String],
+                    Type::Option(Box::new(map_v())),
+                ),
+            ),
+            (
+                "contains".to_string(),
+                Type::function(vec![map_type(), Type::String], Type::Bool),
+            ),
+            (
+                "remove".to_string(),
+                Type::function(vec![map_type(), Type::String], map_type()),
+            ),
+            (
+                "keys".to_string(),
+                Type::function(vec![map_type()], Type::List(Box::new(Type::String))),
+            ),
+            (
+                "values".to_string(),
+                Type::function(vec![map_type()], Type::List(Box::new(map_v()))),
+            ),
+            (
+                "size".to_string(),
+                Type::function(vec![map_type()], Type::Int),
+            ),
+            (
+                "isEmpty".to_string(),
+                Type::function(vec![map_type()], Type::Bool),
+            ),
+            (
+                "fromList".to_string(),
+                Type::function(
+                    vec![Type::List(Box::new(Type::Tuple(vec![Type::String, map_v()])))],
+                    map_type(),
+                ),
+            ),
+            (
+                "toList".to_string(),
+                Type::function(
+                    vec![map_type()],
+                    Type::List(Box::new(Type::Tuple(vec![Type::String, map_v()]))),
+                ),
+            ),
+            (
+                "merge".to_string(),
+                Type::function(vec![map_type(), map_type()], map_type()),
+            ),
+        ]);
+        env.bind("Map", TypeScheme::mono(map_module_type));
+
         // Result module
         let result_type = Type::App {
             constructor: Box::new(Type::Named("Result".to_string())),
@@ -1908,6 +1985,10 @@ impl TypeEnv {
                 "toString".to_string(),
                 Type::function(vec![Type::Int], Type::String),
             ),
+            (
+                "toFloat".to_string(),
+                Type::function(vec![Type::Int], Type::Float),
+            ),
         ]);
         env.bind("Int", TypeScheme::mono(int_module_type));
 
@@ -1917,6 +1998,10 @@ impl TypeEnv {
                 "toString".to_string(),
                 Type::function(vec![Type::Float], Type::String),
             ),
+            (
+                "toInt".to_string(),
+                Type::function(vec![Type::Float], Type::Int),
+            ),
         ]);
         env.bind("Float", TypeScheme::mono(float_module_type));
 
@@ -2003,6 +2088,9 @@ impl TypeEnv {
             Type::Option(inner) => {
                 Type::Option(Box::new(self.expand_type_alias(inner)))
             }
+            Type::Map(k, v) => {
+                Type::Map(Box::new(self.expand_type_alias(k)), Box::new(self.expand_type_alias(v)))
+            }
             Type::Versioned { base, version } => {
                 Type::Versioned {
                     base: Box::new(self.expand_type_alias(base)),
@@ -2163,6 +2251,13 @@ pub fn unify(t1: &Type, t2: &Type) -> Result<Substitution, String> {
         // Option
         (Type::Option(a), Type::Option(b)) => unify(a, b),
 
+        // Map
+        (Type::Map(k1, v1), Type::Map(k2, v2)) => {
+            let s1 = unify(k1, k2)?;
+            let s2 = unify(&v1.apply(&s1), &v2.apply(&s1))?;
+            Ok(s1.compose(&s2))
+        }
+
         // Versioned types
         (
             Type::Versioned {