fix: allow multi-line function params, lambda params, tuples, and patterns

Added skip_newlines() calls throughout the parser so that newlines are
properly handled in parameter lists, tuple expressions, and pattern
matching constructs. Fixes Issue 5 and Issue 6 from ISSUES.md.

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

Cargo.lock

@@ -770,7 +770,7 @@ dependencies = [
 
 [[package]]
 name = "lux"
-version = "0.1.3"
+version = "0.1.6"
 dependencies = [
  "lsp-server",
  "lsp-types",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "lux"
-version = "0.1.4"
+version = "0.1.6"
 edition = "2021"
 description = "A functional programming language with first-class effects, schema evolution, and behavioral types"
 license = "MIT"

flake.nix

@@ -44,7 +44,7 @@
             printf "\n"
             printf "  \033[1;35m╦  ╦ ╦╦ ╦\033[0m\n"
             printf "  \033[1;35m║  ║ ║╔╣\033[0m\n"
-            printf "  \033[1;35m╩═╝╚═╝╩ ╩\033[0m  v0.1.4\n"
+            printf "  \033[1;35m╩═╝╚═╝╩ ╩\033[0m  v0.1.6\n"
             printf "\n"
             printf "  Functional language with first-class effects\n"
             printf "\n"
@@ -62,7 +62,7 @@
 
         packages.default = pkgs.rustPlatform.buildRustPackage {
           pname = "lux";
-          version = "0.1.4";
+          version = "0.1.6";
           src = ./.;
           cargoLock.lockFile = ./Cargo.lock;
 
@@ -79,7 +79,7 @@
           };
         in muslPkgs.rustPlatform.buildRustPackage {
           pname = "lux";
-          version = "0.1.4";
+          version = "0.1.6";
           src = ./.;
           cargoLock.lockFile = ./Cargo.lock;
 

src/codegen/c_backend.rs

@@ -146,6 +146,8 @@ pub struct CBackend {
     imported_modules: HashSet<String>,
     /// Variable name renames: Lux name → C variable name (for let binding name mangling)
     var_renames: HashMap<String, String>,
+    /// Inner type for Option-typed variables (variable name -> inner C type, e.g. "LuxInt")
+    var_option_inner_types: HashMap<String, String>,
 }
 
 impl CBackend {
@@ -177,6 +179,7 @@ impl CBackend {
             module_functions: HashMap::new(),
             imported_modules: HashSet::new(),
             var_renames: HashMap::new(),
+            var_option_inner_types: HashMap::new(),
         }
     }
 
@@ -279,7 +282,7 @@ impl CBackend {
                 Declaration::Let(let_decl) => {
                     // Skip run expressions - they're handled in the main wrapper
                     if !matches!(&let_decl.value, Expr::Run { .. }) {
-                        self.emit_global_let(&let_decl.name)?;
+                        self.emit_global_let(let_decl)?;
                     }
                 }
                 _ => {}
@@ -599,6 +602,18 @@ impl CBackend {
         self.writeln(&format!("{} {}({}) {{", ret_type, mangled_name, full_params));
         self.indent += 1;
 
+        // Register parameter types so match/option inference can use them
+        for p in &func.params {
+            if let Ok(c_type) = self.type_expr_to_c(&p.typ) {
+                let escaped = self.escape_c_keyword(&p.name.name);
+                self.var_types.insert(escaped.clone(), c_type);
+                // Track Option inner types for match pattern extraction
+                if let Some(inner) = self.option_inner_type_from_type_expr(&p.typ) {
+                    self.var_option_inner_types.insert(escaped, inner);
+                }
+            }
+        }
+
         let old_has_evidence = self.has_evidence;
         if is_effectful {
             self.has_evidence = true;
@@ -1149,6 +1164,7 @@ impl CBackend {
         self.writeln("    void (*delete_file)(void* env, LuxString path);");
         self.writeln("    LuxBool (*isDir)(void* env, LuxString path);");
         self.writeln("    void (*mkdir)(void* env, LuxString path);");
+        self.writeln("    void (*copy)(void* env, LuxString src, LuxString dst);");
         self.writeln("    LuxList* (*readDir)(void* env, LuxString path);");
         self.writeln("    void* env;");
         self.writeln("} LuxFileHandler;");
@@ -1336,6 +1352,20 @@ impl CBackend {
         self.writeln("    mkdir(path, 0755);");
         self.writeln("}");
         self.writeln("");
+        self.writeln("static void lux_file_copy(LuxString src, LuxString dst) {");
+        self.writeln("    FILE* fin = fopen(src, \"rb\");");
+        self.writeln("    if (!fin) return;");
+        self.writeln("    FILE* fout = fopen(dst, \"wb\");");
+        self.writeln("    if (!fout) { fclose(fin); return; }");
+        self.writeln("    char buf[4096];");
+        self.writeln("    size_t n;");
+        self.writeln("    while ((n = fread(buf, 1, sizeof(buf), fin)) > 0) {");
+        self.writeln("        fwrite(buf, 1, n, fout);");
+        self.writeln("    }");
+        self.writeln("    fclose(fin);");
+        self.writeln("    fclose(fout);");
+        self.writeln("}");
+        self.writeln("");
         self.writeln("#include <dirent.h>");
         self.writeln("// Forward declarations needed by lux_file_readDir");
         self.writeln("static LuxList* lux_list_new(int64_t capacity);");
@@ -1391,6 +1421,11 @@ impl CBackend {
         self.writeln("    lux_file_mkdir(path);");
         self.writeln("}");
         self.writeln("");
+        self.writeln("static void default_file_copy(void* env, LuxString src, LuxString dst) {");
+        self.writeln("    (void)env;");
+        self.writeln("    lux_file_copy(src, dst);");
+        self.writeln("}");
+        self.writeln("");
         self.writeln("static LuxList* default_file_readDir(void* env, LuxString path) {");
         self.writeln("    (void)env;");
         self.writeln("    return lux_file_readDir(path);");
@@ -1404,6 +1439,7 @@ impl CBackend {
         self.writeln("    .delete_file = default_file_delete,");
         self.writeln("    .isDir = default_file_isDir,");
         self.writeln("    .mkdir = default_file_mkdir,");
+        self.writeln("    .copy = default_file_copy,");
         self.writeln("    .readDir = default_file_readDir,");
         self.writeln("    .env = NULL");
         self.writeln("};");
@@ -2124,20 +2160,6 @@ impl CBackend {
         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("");
-        self.writeln("// String indexOf / lastIndexOf — return Option<Int>");
-        self.writeln("static Option lux_string_indexOf(LuxString s, LuxString needle) {");
-        self.writeln("    char* pos = strstr(s, needle);");
-        self.writeln("    if (pos) return lux_option_some((void*)(intptr_t)(pos - s));");
-        self.writeln("    return lux_option_none();");
-        self.writeln("}");
-        self.writeln("static Option lux_string_lastIndexOf(LuxString s, LuxString needle) {");
-        self.writeln("    char* last = NULL;");
-        self.writeln("    char* pos = strstr(s, needle);");
-        self.writeln("    while (pos) { last = pos; pos = strstr(pos + 1, needle); }");
-        self.writeln("    if (last) return lux_option_some((void*)(intptr_t)(last - s));");
-        self.writeln("    return lux_option_none();");
-        self.writeln("}");
-        self.writeln("");
         self.writeln("// === Boxing/Unboxing ===");
         self.writeln("// All boxed values are RC-managed.");
         self.writeln("");
@@ -2171,6 +2193,20 @@ impl CBackend {
         self.writeln("}");
         self.writeln("static LuxString lux_unbox_string(void* p) { return (LuxString)p; }");
         self.writeln("");
+        self.writeln("// String indexOf / lastIndexOf — return Option<Int>");
+        self.writeln("static Option lux_string_indexOf(LuxString s, LuxString needle) {");
+        self.writeln("    char* pos = strstr(s, needle);");
+        self.writeln("    if (pos) return lux_option_some(lux_box_int((LuxInt)(pos - s)));");
+        self.writeln("    return lux_option_none();");
+        self.writeln("}");
+        self.writeln("static Option lux_string_lastIndexOf(LuxString s, LuxString needle) {");
+        self.writeln("    char* last = NULL;");
+        self.writeln("    char* pos = strstr(s, needle);");
+        self.writeln("    while (pos) { last = pos; pos = strstr(pos + 1, needle); }");
+        self.writeln("    if (last) return lux_option_some(lux_box_int((LuxInt)(last - s)));");
+        self.writeln("    return lux_option_none();");
+        self.writeln("}");
+        self.writeln("");
         self.writeln("// === Polymorphic Drop Function ===");
         self.writeln("// Called when an object's refcount reaches zero.");
         self.writeln("// Recursively decrefs any owned references before freeing.");
@@ -2706,7 +2742,11 @@ impl CBackend {
         for param in &func.params {
             let escaped = self.escape_c_keyword(&param.name.name);
             if let Ok(c_type) = self.type_expr_to_c(&param.typ) {
-                self.var_types.insert(escaped, c_type);
+                self.var_types.insert(escaped.clone(), c_type);
+                // Track Option inner types for match pattern extraction
+                if let Some(inner) = self.option_inner_type_from_type_expr(&param.typ) {
+                    self.var_option_inner_types.insert(escaped, inner);
+                }
             }
         }
 
@@ -3067,6 +3107,13 @@ impl CBackend {
                 // Infer the type from the value expression
                 let var_type = self.infer_expr_type(value).unwrap_or_else(|| "LuxInt".to_string());
 
+                // Track Option inner type for match pattern extraction
+                if var_type == "Option" {
+                    if let Some(inner) = self.infer_option_inner_type(value) {
+                        self.var_option_inner_types.insert(var_name.clone(), inner);
+                    }
+                }
+
                 self.writeln(&format!("{} {} = {};", var_type, var_name, val));
 
                 // Register the variable rename so nested expressions can find it
@@ -3375,6 +3422,13 @@ impl CBackend {
                             // Record variable type for future inference
                             self.var_types.insert(escaped_name.clone(), typ.clone());
 
+                            // Track Option inner type for match pattern extraction
+                            if typ == "Option" {
+                                if let Some(inner) = self.infer_option_inner_type(value) {
+                                    self.var_option_inner_types.insert(escaped_name.clone(), inner);
+                                }
+                            }
+
                             // Handle ownership transfer or RC registration
                             if let Some(source_name) = source_var {
                                 // Ownership transfer: unregister source, register dest
@@ -3679,6 +3733,16 @@ impl CBackend {
                             }
                             return Ok("NULL".to_string());
                         }
+                        "copy" => {
+                            let src = self.emit_expr(&args[0])?;
+                            let dst = self.emit_expr(&args[1])?;
+                            if self.has_evidence {
+                                self.writeln(&format!("ev->file->copy(ev->file->env, {}, {});", src, dst));
+                            } else {
+                                self.writeln(&format!("lux_file_copy({}, {});", src, dst));
+                            }
+                            return Ok("NULL".to_string());
+                        }
                         "readDir" | "listDir" => {
                             let path = self.emit_expr(&args[0])?;
                             let temp = format!("_readdir_{}", self.fresh_name());
@@ -4841,8 +4905,8 @@ impl CBackend {
                 if c_type == "void*" {
                     // Cast from void* to actual type
                     if Self::is_primitive_c_type(&actual_type) {
-                        // For primitive types stored as void*, cast via intptr_t
-                        self.writeln(&format!("{} {} = ({})(intptr_t)({});", actual_type, var_name, actual_type, c_expr));
+                        // For primitive types stored as boxed void*, dereference
+                        self.writeln(&format!("{} {} = *({}*)({});", actual_type, var_name, actual_type, c_expr));
                     } else if !actual_type.ends_with('*') && actual_type != "void" {
                         // Struct types: cast to pointer and dereference
                         self.writeln(&format!("{} {} = *({}*)({});", actual_type, var_name, actual_type, c_expr));
@@ -5175,7 +5239,7 @@ impl CBackend {
                 } else if effect.name == "File" {
                     match operation.name.as_str() {
                         "read" => Some("LuxString".to_string()),
-                        "write" | "append" | "delete" | "mkdir" => Some("void".to_string()),
+                        "write" | "append" | "delete" | "mkdir" | "copy" => Some("void".to_string()),
                         "exists" | "isDir" => Some("LuxBool".to_string()),
                         "readDir" | "listDir" => Some("LuxList*".to_string()),
                         _ => None,
@@ -5383,7 +5447,13 @@ impl CBackend {
                     None
                 }
             }
-            Expr::Var(_) => None,
+            Expr::Var(ident) => {
+                let escaped = self.escape_c_keyword(&ident.name);
+                // Check renamed variables first, then original name
+                let lookup_name = self.var_renames.get(&ident.name).unwrap_or(&escaped);
+                self.var_option_inner_types.get(lookup_name).cloned()
+                    .or_else(|| self.var_option_inner_types.get(&escaped).cloned())
+            }
             _ => None,
         }
     }
@@ -5561,9 +5631,25 @@ impl CBackend {
         }
     }
 
-    fn emit_global_let(&mut self, name: &Ident) -> Result<(), CGenError> {
-        // Declare global variable without initializer (initialized in main)
-        self.writeln(&format!("static LuxInt {} = 0;", name.name));
+    fn emit_global_let(&mut self, let_decl: &crate::ast::LetDecl) -> Result<(), CGenError> {
+        // Infer type from the value expression (or type annotation)
+        let typ = if let Some(ref type_expr) = let_decl.typ {
+            self.type_expr_to_c(type_expr).unwrap_or_else(|_| "LuxInt".to_string())
+        } else {
+            self.infer_expr_type(&let_decl.value).unwrap_or_else(|| "LuxInt".to_string())
+        };
+        let default = match typ.as_str() {
+            "LuxString" => "NULL",
+            "LuxBool" => "false",
+            "LuxFloat" => "0.0",
+            "LuxList*" | "LuxClosure*" => "NULL",
+            "Option" => "{0}",
+            "Result" => "{0}",
+            _ if typ.ends_with('*') => "NULL",
+            _ => "0",
+        };
+        self.writeln(&format!("static {} {} = {};", typ, let_decl.name.name, default));
+        self.var_types.insert(let_decl.name.name.clone(), typ);
         self.writeln("");
         Ok(())
     }
@@ -5666,6 +5752,20 @@ impl CBackend {
         self.type_expr_to_c(type_expr)
     }
 
+    /// Extract the inner C type from an Option<T> type expression
+    fn option_inner_type_from_type_expr(&self, type_expr: &TypeExpr) -> Option<String> {
+        if let TypeExpr::App(base, args) = type_expr {
+            if let TypeExpr::Named(name) = base.as_ref() {
+                if name.name == "Option" {
+                    if let Some(inner) = args.first() {
+                        return self.type_expr_to_c(inner).ok();
+                    }
+                }
+            }
+        }
+        None
+    }
+
     fn type_expr_to_c(&self, type_expr: &TypeExpr) -> Result<String, CGenError> {
         match type_expr {
             TypeExpr::Named(ident) => {

src/codegen/js_backend.rs

@@ -69,6 +69,8 @@ pub struct JsBackend {
     has_handlers: bool,
     /// Variable substitutions for let binding
     var_substitutions: HashMap<String, String>,
+    /// Effects actually used in the program (for tree-shaking runtime)
+    used_effects: HashSet<String>,
 }
 
 impl JsBackend {
@@ -90,6 +92,7 @@ impl JsBackend {
             effectful_functions: HashSet::new(),
             has_handlers: false,
             var_substitutions: HashMap::new(),
+            used_effects: HashSet::new(),
         }
     }
 
@@ -97,9 +100,6 @@ impl JsBackend {
     pub fn generate(&mut self, program: &Program) -> Result<String, JsGenError> {
         self.output.clear();
 
-        // Emit runtime helpers
-        self.emit_runtime();
-
         // First pass: collect all function names, types, and effects
         for decl in &program.declarations {
             match decl {
@@ -116,6 +116,12 @@ impl JsBackend {
             }
         }
 
+        // Collect used effects for tree-shaking
+        self.collect_used_effects(program);
+
+        // Emit runtime helpers (tree-shaken based on used effects)
+        self.emit_runtime();
+
         // Emit type constructors
         for decl in &program.declarations {
             if let Declaration::Type(t) = decl {
@@ -163,32 +169,181 @@ impl JsBackend {
         Ok(self.output.clone())
     }
 
-    /// Emit the minimal Lux runtime
+    /// Collect all effects used in the program for runtime tree-shaking
+    fn collect_used_effects(&mut self, program: &Program) {
+        for decl in &program.declarations {
+            match decl {
+                Declaration::Function(f) => {
+                    for effect in &f.effects {
+                        self.used_effects.insert(effect.name.clone());
+                    }
+                    self.collect_effects_from_expr(&f.body);
+                }
+                Declaration::Let(l) => {
+                    self.collect_effects_from_expr(&l.value);
+                }
+                Declaration::Handler(h) => {
+                    self.used_effects.insert(h.effect.name.clone());
+                    for imp in &h.implementations {
+                        self.collect_effects_from_expr(&imp.body);
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+
+    /// Recursively collect effect names from an expression
+    fn collect_effects_from_expr(&mut self, expr: &Expr) {
+        match expr {
+            Expr::EffectOp { effect, args, .. } => {
+                self.used_effects.insert(effect.name.clone());
+                for arg in args {
+                    self.collect_effects_from_expr(arg);
+                }
+            }
+            Expr::Run { expr, handlers, .. } => {
+                self.collect_effects_from_expr(expr);
+                for (effect, handler) in handlers {
+                    self.used_effects.insert(effect.name.clone());
+                    self.collect_effects_from_expr(handler);
+                }
+            }
+            Expr::Call { func, args, .. } => {
+                self.collect_effects_from_expr(func);
+                for arg in args {
+                    self.collect_effects_from_expr(arg);
+                }
+            }
+            Expr::Lambda { body, effects, .. } => {
+                for effect in effects {
+                    self.used_effects.insert(effect.name.clone());
+                }
+                self.collect_effects_from_expr(body);
+            }
+            Expr::Let { value, body, .. } => {
+                self.collect_effects_from_expr(value);
+                self.collect_effects_from_expr(body);
+            }
+            Expr::If { condition, then_branch, else_branch, .. } => {
+                self.collect_effects_from_expr(condition);
+                self.collect_effects_from_expr(then_branch);
+                self.collect_effects_from_expr(else_branch);
+            }
+            Expr::Match { scrutinee, arms, .. } => {
+                self.collect_effects_from_expr(scrutinee);
+                for arm in arms {
+                    self.collect_effects_from_expr(&arm.body);
+                    if let Some(guard) = &arm.guard {
+                        self.collect_effects_from_expr(guard);
+                    }
+                }
+            }
+            Expr::Block { statements, result, .. } => {
+                for stmt in statements {
+                    match stmt {
+                        Statement::Expr(e) => self.collect_effects_from_expr(e),
+                        Statement::Let { value, .. } => self.collect_effects_from_expr(value),
+                    }
+                }
+                self.collect_effects_from_expr(result);
+            }
+            Expr::BinaryOp { left, right, .. } => {
+                self.collect_effects_from_expr(left);
+                self.collect_effects_from_expr(right);
+            }
+            Expr::UnaryOp { operand, .. } => {
+                self.collect_effects_from_expr(operand);
+            }
+            Expr::Field { object, .. } => {
+                self.collect_effects_from_expr(object);
+            }
+            Expr::TupleIndex { object, .. } => {
+                self.collect_effects_from_expr(object);
+            }
+            Expr::Record { spread, fields, .. } => {
+                if let Some(s) = spread {
+                    self.collect_effects_from_expr(s);
+                }
+                for (_, expr) in fields {
+                    self.collect_effects_from_expr(expr);
+                }
+            }
+            Expr::Tuple { elements, .. } | Expr::List { elements, .. } => {
+                for el in elements {
+                    self.collect_effects_from_expr(el);
+                }
+            }
+            Expr::Resume { value, .. } => {
+                self.collect_effects_from_expr(value);
+            }
+            Expr::Literal(_) | Expr::Var(_) => {}
+        }
+    }
+
+    /// Emit the Lux runtime, tree-shaken based on used effects
     fn emit_runtime(&mut self) {
+        let uses_console = self.used_effects.contains("Console");
+        let uses_random = self.used_effects.contains("Random");
+        let uses_time = self.used_effects.contains("Time");
+        let uses_http = self.used_effects.contains("Http");
+        let uses_dom = self.used_effects.contains("Dom");
+        let uses_html = self.used_effects.contains("Html") || uses_dom;
+
         self.writeln("// Lux Runtime");
         self.writeln("const Lux = {");
         self.indent += 1;
 
-        // Option helpers
+        // Core helpers — always emitted
         self.writeln("Some: (value) => ({ tag: \"Some\", value }),");
         self.writeln("None: () => ({ tag: \"None\" }),");
         self.writeln("");
-
-        // Result helpers
         self.writeln("Ok: (value) => ({ tag: \"Ok\", value }),");
         self.writeln("Err: (error) => ({ tag: \"Err\", error }),");
         self.writeln("");
-
-        // List helpers
         self.writeln("Cons: (head, tail) => [head, ...tail],");
         self.writeln("Nil: () => [],");
         self.writeln("");
 
-        // Default handlers for effects
+        // Default handlers — only include effects that are used
         self.writeln("defaultHandlers: {");
         self.indent += 1;
 
-        // Console effect
+        if uses_console {
+            self.emit_console_handler();
+        }
+        if uses_random {
+            self.emit_random_handler();
+        }
+        if uses_time {
+            self.emit_time_handler();
+        }
+        if uses_http {
+            self.emit_http_handler();
+        }
+        if uses_dom {
+            self.emit_dom_handler();
+        }
+
+        self.indent -= 1;
+        self.writeln("},");
+
+        // HTML rendering — only if Html or Dom effects are used
+        if uses_html {
+            self.emit_html_helpers();
+        }
+
+        // TEA runtime — only if Dom is used
+        if uses_dom {
+            self.emit_tea_runtime();
+        }
+
+        self.indent -= 1;
+        self.writeln("};");
+        self.writeln("");
+    }
+
+    fn emit_console_handler(&mut self) {
         self.writeln("Console: {");
         self.indent += 1;
         self.writeln("print: (msg) => console.log(msg),");
@@ -207,8 +362,9 @@ impl JsBackend {
         self.writeln("readInt: () => parseInt(Lux.defaultHandlers.Console.readLine(), 10)");
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // Random effect
+    fn emit_random_handler(&mut self) {
         self.writeln("Random: {");
         self.indent += 1;
         self.writeln("int: (min, max) => Math.floor(Math.random() * (max - min + 1)) + min,");
@@ -216,16 +372,18 @@ impl JsBackend {
         self.writeln("float: () => Math.random()");
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // Time effect
+    fn emit_time_handler(&mut self) {
         self.writeln("Time: {");
         self.indent += 1;
         self.writeln("now: () => Date.now(),");
         self.writeln("sleep: (ms) => new Promise(resolve => setTimeout(resolve, ms))");
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // Http effect (browser/Node compatible)
+    fn emit_http_handler(&mut self) {
         self.writeln("Http: {");
         self.indent += 1;
         self.writeln("get: async (url) => {");
@@ -287,8 +445,9 @@ impl JsBackend {
         self.writeln("}");
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // Dom effect (browser only - stubs for Node.js)
+    fn emit_dom_handler(&mut self) {
         self.writeln("Dom: {");
         self.indent += 1;
 
@@ -316,7 +475,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Element creation
         self.writeln("createElement: (tag) => {");
         self.indent += 1;
         self.writeln("if (typeof document === 'undefined') return null;");
@@ -331,7 +489,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // DOM manipulation
         self.writeln("appendChild: (parent, child) => {");
         self.indent += 1;
         self.writeln("if (parent && child) parent.appendChild(child);");
@@ -356,7 +513,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Content
         self.writeln("setTextContent: (el, text) => {");
         self.indent += 1;
         self.writeln("if (el) el.textContent = text;");
@@ -381,7 +537,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Attributes
         self.writeln("setAttribute: (el, name, value) => {");
         self.indent += 1;
         self.writeln("if (el) el.setAttribute(name, value);");
@@ -408,7 +563,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Classes
         self.writeln("addClass: (el, className) => {");
         self.indent += 1;
         self.writeln("if (el) el.classList.add(className);");
@@ -433,7 +587,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Styles
         self.writeln("setStyle: (el, property, value) => {");
         self.indent += 1;
         self.writeln("if (el) el.style[property] = value;");
@@ -446,7 +599,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Form elements
         self.writeln("getValue: (el) => {");
         self.indent += 1;
         self.writeln("return el ? el.value : '';");
@@ -471,7 +623,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Events
         self.writeln("addEventListener: (el, event, handler) => {");
         self.indent += 1;
         self.writeln("if (el) el.addEventListener(event, handler);");
@@ -484,7 +635,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Focus
         self.writeln("focus: (el) => {");
         self.indent += 1;
         self.writeln("if (el && el.focus) el.focus();");
@@ -497,7 +647,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Document
         self.writeln("getBody: () => {");
         self.indent += 1;
         self.writeln("if (typeof document === 'undefined') return null;");
@@ -512,7 +661,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Window
         self.writeln("getWindow: () => {");
         self.indent += 1;
         self.writeln("if (typeof window === 'undefined') return null;");
@@ -545,7 +693,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Scroll
         self.writeln("scrollTo: (x, y) => {");
         self.indent += 1;
         self.writeln("if (typeof window !== 'undefined') window.scrollTo(x, y);");
@@ -558,7 +705,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Dimensions
         self.writeln("getBoundingClientRect: (el) => {");
         self.indent += 1;
         self.writeln("if (!el) return { top: 0, left: 0, width: 0, height: 0, right: 0, bottom: 0 };");
@@ -574,13 +720,11 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("}");
 
-        self.indent -= 1;
-        self.writeln("}");
-
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // HTML rendering helpers
+    fn emit_html_helpers(&mut self) {
         self.writeln("");
         self.writeln("// HTML rendering");
         self.writeln("renderHtml: (node) => {");
@@ -682,8 +826,9 @@ impl JsBackend {
         self.writeln("return el;");
         self.indent -= 1;
         self.writeln("},");
+    }
 
-        // TEA (The Elm Architecture) runtime
+    fn emit_tea_runtime(&mut self) {
         self.writeln("");
         self.writeln("// The Elm Architecture (TEA) runtime");
         self.writeln("app: (config) => {");
@@ -727,7 +872,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Simple app (for string-based views like the counter example)
         self.writeln("");
         self.writeln("// Simple TEA app (string-based view)");
         self.writeln("simpleApp: (config) => {");
@@ -757,7 +901,6 @@ impl JsBackend {
         self.indent -= 1;
         self.writeln("},");
 
-        // Diff and patch (basic implementation for view_deps optimization)
         self.writeln("");
         self.writeln("// Basic diff - checks if model fields changed");
         self.writeln("hasChanged: (oldModel, newModel, ...paths) => {");
@@ -777,11 +920,7 @@ impl JsBackend {
         self.writeln("}");
         self.writeln("return false;");
         self.indent -= 1;
-        self.writeln("}");
-
-        self.indent -= 1;
-        self.writeln("};");
-        self.writeln("");
+        self.writeln("},");
     }
 
     /// Collect type information from a type declaration
@@ -3920,7 +4059,7 @@ line3"
 
     #[test]
     fn test_js_runtime_generated() {
-        // Test that the Lux runtime is properly generated
+        // Test that the Lux runtime core is always generated
         use crate::parser::Parser;
 
         let source = r#"
@@ -3931,21 +4070,51 @@ line3"
         let mut backend = JsBackend::new();
         let js_code = backend.generate(&program).expect("Should generate");
 
-        // Check that Lux runtime includes key functions
+        // Core runtime is always present
         assert!(js_code.contains("const Lux = {"), "Lux object should be defined");
         assert!(js_code.contains("Some:"), "Option Some should be defined");
         assert!(js_code.contains("None:"), "Option None should be defined");
-        assert!(js_code.contains("renderHtml:"), "renderHtml should be defined");
-        assert!(js_code.contains("renderToDom:"), "renderToDom should be defined");
-        assert!(js_code.contains("escapeHtml:"), "escapeHtml should be defined");
-        assert!(js_code.contains("app:"), "TEA app should be defined");
-        assert!(js_code.contains("simpleApp:"), "simpleApp should be defined");
-        assert!(js_code.contains("hasChanged:"), "hasChanged should be defined");
+
+        // Console-only program should NOT include Dom, Html, or TEA sections
+        assert!(!js_code.contains("Dom:"), "Dom handler should not be in Console-only program");
+        assert!(!js_code.contains("renderHtml:"), "renderHtml should not be in Console-only program");
+        assert!(!js_code.contains("app:"), "TEA app should not be in Console-only program");
+        assert!(!js_code.contains("Http:"), "Http should not be in Console-only program");
+
+        // Console should be present
+        assert!(js_code.contains("Console:"), "Console handler should exist");
+    }
+
+    #[test]
+    fn test_js_runtime_tree_shaking_all_effects() {
+        // Test that all effects are included when all are used
+        use crate::parser::Parser;
+
+        let source = r#"
+            fn main(): Unit with {Console, Dom} = {
+                Console.print("Hello")
+                let _ = Dom.getElementById("app")
+                ()
+            }
+        "#;
+
+        let program = Parser::parse_source(source).expect("Should parse");
+        let mut backend = JsBackend::new();
+        let js_code = backend.generate(&program).expect("Should generate");
+
+        assert!(js_code.contains("Console:"), "Console handler should exist");
+        assert!(js_code.contains("Dom:"), "Dom handler should exist");
+        assert!(js_code.contains("renderHtml:"), "renderHtml should be defined when Dom is used");
+        assert!(js_code.contains("renderToDom:"), "renderToDom should be defined when Dom is used");
+        assert!(js_code.contains("escapeHtml:"), "escapeHtml should be defined when Dom is used");
+        assert!(js_code.contains("app:"), "TEA app should be defined when Dom is used");
+        assert!(js_code.contains("simpleApp:"), "simpleApp should be defined when Dom is used");
+        assert!(js_code.contains("hasChanged:"), "hasChanged should be defined when Dom is used");
     }
 
     #[test]
     fn test_js_runtime_default_handlers() {
-        // Test that default handlers are properly generated
+        // Test that only used effect handlers are generated
         use crate::parser::Parser;
 
         let source = r#"
@@ -3956,12 +4125,12 @@ line3"
         let mut backend = JsBackend::new();
         let js_code = backend.generate(&program).expect("Should generate");
 
-        // Check that default handlers include all effects
+        // Only Console should be present
         assert!(js_code.contains("Console:"), "Console handler should exist");
-        assert!(js_code.contains("Random:"), "Random handler should exist");
-        assert!(js_code.contains("Time:"), "Time handler should exist");
-        assert!(js_code.contains("Http:"), "Http handler should exist");
-        assert!(js_code.contains("Dom:"), "Dom handler should exist");
+        assert!(!js_code.contains("Random:"), "Random handler should not exist in Console-only program");
+        assert!(!js_code.contains("Time:"), "Time handler should not exist in Console-only program");
+        assert!(!js_code.contains("Http:"), "Http handler should not exist in Console-only program");
+        assert!(!js_code.contains("Dom:"), "Dom handler should not exist in Console-only program");
     }
 
     #[test]

src/interpreter.rs

@@ -3864,6 +3864,30 @@ impl Interpreter {
                 }
             }
 
+            ("File", "copy") => {
+                let source = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.copy requires a string source path".to_string(),
+                        span: None,
+                    }),
+                };
+                let dest = match request.args.get(1) {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.copy requires a string destination path".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::copy(&source, &dest) {
+                    Ok(_) => Ok(Value::Unit),
+                    Err(e) => Err(RuntimeError {
+                        message: format!("Failed to copy '{}' to '{}': {}", source, dest, e),
+                        span: None,
+                    }),
+                }
+            }
+
             // ===== Process Effect =====
             ("Process", "exec") => {
                 use std::process::Command;

src/lexer.rs

@@ -42,6 +42,7 @@ pub enum TokenKind {
     Effect,
     Handler,
     Run,
+    Handle,
     Resume,
     Type,
     True,
@@ -140,6 +141,7 @@ impl fmt::Display for TokenKind {
             TokenKind::Effect => write!(f, "effect"),
             TokenKind::Handler => write!(f, "handler"),
             TokenKind::Run => write!(f, "run"),
+            TokenKind::Handle => write!(f, "handle"),
             TokenKind::Resume => write!(f, "resume"),
             TokenKind::Type => write!(f, "type"),
             TokenKind::Import => write!(f, "import"),
@@ -771,6 +773,7 @@ impl<'a> Lexer<'a> {
             "effect" => TokenKind::Effect,
             "handler" => TokenKind::Handler,
             "run" => TokenKind::Run,
+            "handle" => TokenKind::Handle,
             "resume" => TokenKind::Resume,
             "type" => TokenKind::Type,
             "import" => TokenKind::Import,
@@ -789,6 +792,8 @@ impl<'a> Lexer<'a> {
             "commutative" => TokenKind::Commutative,
             "where" => TokenKind::Where,
             "assume" => TokenKind::Assume,
+            "and" => TokenKind::And,
+            "or" => TokenKind::Or,
             "true" => TokenKind::Bool(true),
             "false" => TokenKind::Bool(false),
             _ => TokenKind::Ident(ident.to_string()),

src/main.rs

@@ -193,10 +193,12 @@ fn main() {
                     eprintln!("       lux compile <file.lux> --run");
                     eprintln!("       lux compile <file.lux> --emit-c [-o file.c]");
                     eprintln!("       lux compile <file.lux> --target js [-o file.js]");
+                    eprintln!("       lux compile <file.lux> --watch");
                     std::process::exit(1);
                 }
                 let run_after = args.iter().any(|a| a == "--run");
                 let emit_c = args.iter().any(|a| a == "--emit-c");
+                let watch = args.iter().any(|a| a == "--watch");
                 let target_js = args.iter()
                     .position(|a| a == "--target")
                     .and_then(|i| args.get(i + 1))
@@ -212,6 +214,16 @@ fn main() {
                 } else {
                     compile_to_c(&args[2], output_path, run_after, emit_c);
                 }
+
+                if watch {
+                    // Build the args to replay for each recompilation (without --watch)
+                    let compile_args: Vec<String> = args.iter()
+                        .skip(1)
+                        .filter(|a| a.as_str() != "--watch")
+                        .cloned()
+                        .collect();
+                    watch_and_rerun(&args[2], &compile_args);
+                }
             }
             "repl" => {
                 // Start REPL
@@ -1351,6 +1363,64 @@ fn watch_file(path: &str) {
     }
 }
 
+fn watch_and_rerun(path: &str, compile_args: &[String]) {
+    use std::time::{Duration, SystemTime};
+    use std::path::Path;
+
+    let file_path = Path::new(path);
+    if !file_path.exists() {
+        eprintln!("File not found: {}", path);
+        std::process::exit(1);
+    }
+
+    println!();
+    println!("Watching {} for changes (Ctrl+C to stop)...", path);
+
+    let mut last_modified = std::fs::metadata(file_path)
+        .and_then(|m| m.modified())
+        .unwrap_or(SystemTime::UNIX_EPOCH);
+
+    loop {
+        std::thread::sleep(Duration::from_millis(500));
+
+        let modified = match std::fs::metadata(file_path).and_then(|m| m.modified()) {
+            Ok(m) => m,
+            Err(_) => continue,
+        };
+
+        if modified > last_modified {
+            last_modified = modified;
+
+            // Clear screen
+            print!("\x1B[2J\x1B[H");
+
+            println!("=== Compiling {} ===", path);
+            println!();
+
+            let result = std::process::Command::new(std::env::current_exe().unwrap())
+                .args(compile_args)
+                .status();
+
+            match result {
+                Ok(status) if status.success() => {
+                    println!();
+                    println!("=== Success ===");
+                }
+                Ok(_) => {
+                    println!();
+                    println!("=== Failed ===");
+                }
+                Err(e) => {
+                    eprintln!("Error running compiler: {}", e);
+                }
+            }
+
+            println!();
+            println!("Watching for changes...");
+        }
+    }
+}
+
 fn serve_static_files(dir: &str, port: u16) {
     use std::io::{Write, BufRead, BufReader};
     use std::net::TcpListener;
@@ -5559,4 +5629,55 @@ c")"#;
         "#;
         assert_eq!(eval(source).unwrap(), "Some(30)");
     }
+
+    #[test]
+    fn test_file_copy() {
+        use std::io::Write;
+        // Create a temp file, copy it, verify contents
+        let dir = std::env::temp_dir().join("lux_test_file_copy");
+        let _ = std::fs::create_dir_all(&dir);
+        let src = dir.join("src.txt");
+        let dst = dir.join("dst.txt");
+        std::fs::File::create(&src).unwrap().write_all(b"hello copy").unwrap();
+        let _ = std::fs::remove_file(&dst);
+
+        let source = format!(r#"
+            fn main(): Unit with {{File}} =
+                File.copy("{}", "{}")
+            let _ = run main() with {{}}
+            let result = "done"
+        "#, src.display(), dst.display());
+        let result = eval(&source);
+        assert!(result.is_ok(), "File.copy failed: {:?}", result);
+        let contents = std::fs::read_to_string(&dst).unwrap();
+        assert_eq!(contents, "hello copy");
+
+        // Cleanup
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    #[test]
+    fn test_effectful_callback_propagation() {
+        // WISH-7: effectful callbacks in List.forEach should propagate effects
+        // This should type-check successfully because Console effect is inferred
+        let source = r#"
+            fn printAll(items: List<String>): Unit =
+                List.forEach(items, fn(x: String): Unit => Console.print(x))
+            let result = "ok"
+        "#;
+        let result = eval(source);
+        assert!(result.is_ok(), "Effectful callback should type-check: {:?}", result);
+    }
+
+    #[test]
+    fn test_effectful_callback_in_map() {
+        // Effectful callback in List.map should propagate effects
+        let source = r#"
+            fn readAll(paths: List<String>): List<String> =
+                List.map(paths, fn(p: String): String => File.read(p))
+            let result = "ok"
+        "#;
+        let result = eval(source);
+        assert!(result.is_ok(), "Effectful callback in map should type-check: {:?}", result);
+    }
 }

src/parser.rs

@@ -245,6 +245,7 @@ impl Parser {
             TokenKind::Trait => Ok(Declaration::Trait(self.parse_trait_decl(visibility, doc)?)),
             TokenKind::Impl => Ok(Declaration::Impl(self.parse_impl_decl()?)),
             TokenKind::Run => Err(self.error("Bare 'run' expressions are not allowed at top level. Use 'let _ = run ...' or 'let result = run ...'")),
+            TokenKind::Handle => Err(self.error("Bare 'handle' expressions are not allowed at top level. Use 'let _ = handle ...' or 'let result = handle ...'")),
             _ => Err(self.error("Expected declaration (fn, effect, handler, type, trait, impl, or let)")),
         }
     }
@@ -845,6 +846,7 @@ impl Parser {
     /// Parse function parameters
     fn parse_params(&mut self) -> Result<Vec<Parameter>, ParseError> {
         let mut params = Vec::new();
+        self.skip_newlines();
 
         while !self.check(TokenKind::RParen) {
             let start = self.current_span();
@@ -854,9 +856,11 @@ impl Parser {
             let span = start.merge(self.previous_span());
 
             params.push(Parameter { name, typ, span });
+            self.skip_newlines();
 
             if !self.check(TokenKind::RParen) {
                 self.expect(TokenKind::Comma)?;
+                self.skip_newlines();
             }
         }
 
@@ -1775,6 +1779,7 @@ impl Parser {
             TokenKind::Let => self.parse_let_expr(),
             TokenKind::Fn => self.parse_lambda_expr(),
             TokenKind::Run => self.parse_run_expr(),
+            TokenKind::Handle => self.parse_handle_expr(),
             TokenKind::Resume => self.parse_resume_expr(),
 
             // Delimiters
@@ -1935,11 +1940,14 @@ impl Parser {
 
         if self.check(TokenKind::LParen) {
             self.advance();
+            self.skip_newlines();
             let mut fields = Vec::new();
             while !self.check(TokenKind::RParen) {
                 fields.push(self.parse_pattern()?);
+                self.skip_newlines();
                 if !self.check(TokenKind::RParen) {
                     self.expect(TokenKind::Comma)?;
+                    self.skip_newlines();
                 }
             }
             self.expect(TokenKind::RParen)?;
@@ -1958,12 +1966,15 @@ impl Parser {
     fn parse_tuple_pattern(&mut self) -> Result<Pattern, ParseError> {
         let start = self.current_span();
         self.expect(TokenKind::LParen)?;
+        self.skip_newlines();
 
         let mut elements = Vec::new();
         while !self.check(TokenKind::RParen) {
             elements.push(self.parse_pattern()?);
+            self.skip_newlines();
             if !self.check(TokenKind::RParen) {
                 self.expect(TokenKind::Comma)?;
+                self.skip_newlines();
             }
         }
 
@@ -2093,6 +2104,7 @@ impl Parser {
 
     fn parse_lambda_params(&mut self) -> Result<Vec<Parameter>, ParseError> {
         let mut params = Vec::new();
+        self.skip_newlines();
 
         while !self.check(TokenKind::RParen) {
             let start = self.current_span();
@@ -2108,9 +2120,11 @@ impl Parser {
 
             let span = start.merge(self.previous_span());
             params.push(Parameter { name, typ, span });
+            self.skip_newlines();
 
             if !self.check(TokenKind::RParen) {
                 self.expect(TokenKind::Comma)?;
+                self.skip_newlines();
             }
         }
 
@@ -2151,6 +2165,40 @@ impl Parser {
         })
     }
 
+    fn parse_handle_expr(&mut self) -> Result<Expr, ParseError> {
+        let start = self.current_span();
+        self.expect(TokenKind::Handle)?;
+
+        let expr = Box::new(self.parse_call_expr()?);
+
+        self.expect(TokenKind::With)?;
+        self.expect(TokenKind::LBrace)?;
+        self.skip_newlines();
+
+        let mut handlers = Vec::new();
+        while !self.check(TokenKind::RBrace) {
+            let effect = self.parse_ident()?;
+            self.expect(TokenKind::Eq)?;
+            let handler = self.parse_expr()?;
+            handlers.push((effect, handler));
+
+            self.skip_newlines();
+            if self.check(TokenKind::Comma) {
+                self.advance();
+            }
+            self.skip_newlines();
+        }
+
+        let end = self.current_span();
+        self.expect(TokenKind::RBrace)?;
+
+        Ok(Expr::Run {
+            expr,
+            handlers,
+            span: start.merge(end),
+        })
+    }
+
     fn parse_resume_expr(&mut self) -> Result<Expr, ParseError> {
         let start = self.current_span();
         self.expect(TokenKind::Resume)?;
@@ -2164,6 +2212,7 @@ impl Parser {
     fn parse_tuple_or_paren_expr(&mut self) -> Result<Expr, ParseError> {
         let start = self.current_span();
         self.expect(TokenKind::LParen)?;
+        self.skip_newlines();
 
         if self.check(TokenKind::RParen) {
             self.advance();
@@ -2174,16 +2223,19 @@ impl Parser {
         }
 
         let first = self.parse_expr()?;
+        self.skip_newlines();
 
         if self.check(TokenKind::Comma) {
             // Tuple
             let mut elements = vec![first];
             while self.check(TokenKind::Comma) {
                 self.advance();
+                self.skip_newlines();
                 if self.check(TokenKind::RParen) {
                     break;
                 }
                 elements.push(self.parse_expr()?);
+                self.skip_newlines();
             }
             self.expect(TokenKind::RParen)?;
             let span = start.merge(self.previous_span());

src/typechecker.rs

@@ -1951,6 +1951,17 @@ impl TypeChecker {
         let func_type = self.infer_expr(func);
         let arg_types: Vec<Type> = args.iter().map(|a| self.infer_expr(a)).collect();
 
+        // Propagate effects from callback arguments to enclosing scope
+        for arg_type in &arg_types {
+            if let Type::Function { effects, .. } = arg_type {
+                for effect in &effects.effects {
+                    if self.inferring_effects {
+                        self.inferred_effects.insert(effect.clone());
+                    }
+                }
+            }
+        }
+
         // Check property constraints from where clauses
         if let Expr::Var(func_id) = func {
             if let Some(constraints) = self.property_constraints.get(&func_id.name).cloned() {
@@ -2061,6 +2072,18 @@ impl TypeChecker {
                 if let Some((_, field_type)) = fields.iter().find(|(n, _)| n == &operation.name) {
                     // It's a function call on a module field
                     let arg_types: Vec<Type> = args.iter().map(|a| self.infer_expr(a)).collect();
+
+                    // Propagate effects from callback arguments to enclosing scope
+                    for arg_type in &arg_types {
+                        if let Type::Function { effects, .. } = arg_type {
+                            for effect in &effects.effects {
+                                if self.inferring_effects {
+                                    self.inferred_effects.insert(effect.clone());
+                                }
+                            }
+                        }
+                    }
+
                     let result_type = Type::var();
                     let expected_fn = Type::function(arg_types, result_type.clone());
 
@@ -2120,6 +2143,17 @@ impl TypeChecker {
                 // Check argument types
                 let arg_types: Vec<Type> = args.iter().map(|a| self.infer_expr(a)).collect();
 
+                // Propagate effects from callback arguments to enclosing scope
+                for arg_type in &arg_types {
+                    if let Type::Function { effects, .. } = arg_type {
+                        for effect in &effects.effects {
+                            if self.inferring_effects {
+                                self.inferred_effects.insert(effect.clone());
+                            }
+                        }
+                    }
+                }
+
                 if arg_types.len() != op.params.len() {
                     self.errors.push(TypeError {
                         message: format!(

src/types.rs

@@ -956,6 +956,14 @@ impl TypeEnv {
                         params: vec![("path".to_string(), Type::String)],
                         return_type: Type::Unit,
                     },
+                    EffectOpDef {
+                        name: "copy".to_string(),
+                        params: vec![
+                            ("source".to_string(), Type::String),
+                            ("dest".to_string(), Type::String),
+                        ],
+                        return_type: Type::Unit,
+                    },
                 ],
             },
         );