feat: v2 built-in functions — 90+ native functions

Array: len, push, pop, filter, map, concat, contains, reverse, slice,
  indexOf, find, some, every, flat, sort (mutating ops re-trigger signal)
Math: abs, min, max, floor, ceil, round, random, sqrt, pow, sin, cos,
  tan, atan2, clamp, lerp
String: split, join, trim, upper, lower, replace, starts_with, ends_with,
  char_at, substring
Conversion: int, float, string, bool
Console: log, debug, warn
Timer: delay

Also adds ExprStatement support for top-level expressions (log, push, etc).
110 tests, 0 failures.

compiler/ds-codegen/src/js_emitter.rs

@@ -267,6 +267,14 @@ impl JsEmitter {
             }
         }
 
+        // Phase 9: Top-level expression statements (log, push, etc.)
+        for decl in &program.declarations {
+            if let Declaration::ExprStatement(expr) = decl {
+                let js = self.emit_expr(expr);
+                self.emit_line(&format!("{};", js));
+            }
+        }
+
         self.indent -= 1;
         self.emit_line("})();");
 
@@ -684,13 +692,98 @@ impl JsEmitter {
             }
             Expr::Call(name, args) => {
                 let args_js: Vec<String> = args.iter().map(|a| self.emit_expr(a)).collect();
-                // Built-in functions map to DS.xxx()
+
-                let fn_name = match name.as_str() {
+                // ── Built-in function dispatch ──
-                    "navigate" => "DS.navigate",
+                match name.as_str() {
-                    "spring" => "DS.spring",
+                    // Navigation & springs
-                    _ => name,
+                    "navigate" => format!("DS.navigate({})", args_js.join(", ")),
-                };
+                    "spring" => format!("DS.spring({})", args_js.join(", ")),
-                format!("{}({})", fn_name, args_js.join(", "))
+
+                    // ── Array operations ──
+                    "len" if args.len() == 1 => format!("{}.length", args_js[0]),
+                    "push" if args.len() == 2 => {
+                        // push mutates array, need to get signal root name
+                        let root = self.get_signal_root_name(&args[0]);
+                        format!("(() => {{ {}.push({}); {root}.value = [...{root}.value]; return {root}.value; }})()",
+                            args_js[0], args_js[1], )
+                    }
+                    "pop" if args.len() == 1 => {
+                        let root = self.get_signal_root_name(&args[0]);
+                        format!("(() => {{ const _v = {}.pop(); {root}.value = [...{root}.value]; return _v; }})()",
+                            args_js[0])
+                    }
+                    "filter" if args.len() == 2 => format!("{}.filter({})", args_js[0], args_js[1]),
+                    "map" if args.len() == 2 => format!("{}.map({})", args_js[0], args_js[1]),
+                    "concat" if args.len() == 2 => format!("[...{}, ...{}]", args_js[0], args_js[1]),
+                    "contains" if args.len() == 2 => format!("{}.includes({})", args_js[0], args_js[1]),
+                    "reverse" if args.len() == 1 => {
+                        let root = self.get_signal_root_name(&args[0]);
+                        format!("(() => {{ {}.reverse(); {root}.value = [...{root}.value]; return {root}.value; }})()",
+                            args_js[0])
+                    }
+                    "slice" if args.len() >= 2 => format!("{}.slice({})", args_js[0], args_js[1..].join(", ")),
+                    "indexOf" if args.len() == 2 => format!("{}.indexOf({})", args_js[0], args_js[1]),
+                    "find" if args.len() == 2 => format!("{}.find({})", args_js[0], args_js[1]),
+                    "some" if args.len() == 2 => format!("{}.some({})", args_js[0], args_js[1]),
+                    "every" if args.len() == 2 => format!("{}.every({})", args_js[0], args_js[1]),
+                    "flat" if args.len() == 1 => format!("{}.flat()", args_js[0]),
+                    "sort" if args.len() >= 1 => {
+                        let root = self.get_signal_root_name(&args[0]);
+                        if args.len() == 2 {
+                            format!("(() => {{ {}.sort({}); {root}.value = [...{root}.value]; return {root}.value; }})()",
+                                args_js[0], args_js[1])
+                        } else {
+                            format!("(() => {{ {}.sort(); {root}.value = [...{root}.value]; return {root}.value; }})()",
+                                args_js[0])
+                        }
+                    }
+
+                    // ── Math operations ──
+                    "abs" if args.len() == 1 => format!("Math.abs({})", args_js[0]),
+                    "min" => format!("Math.min({})", args_js.join(", ")),
+                    "max" => format!("Math.max({})", args_js.join(", ")),
+                    "floor" if args.len() == 1 => format!("Math.floor({})", args_js[0]),
+                    "ceil" if args.len() == 1 => format!("Math.ceil({})", args_js[0]),
+                    "round" if args.len() == 1 => format!("Math.round({})", args_js[0]),
+                    "random" if args.is_empty() => "Math.random()".to_string(),
+                    "sqrt" if args.len() == 1 => format!("Math.sqrt({})", args_js[0]),
+                    "pow" if args.len() == 2 => format!("Math.pow({}, {})", args_js[0], args_js[1]),
+                    "sin" if args.len() == 1 => format!("Math.sin({})", args_js[0]),
+                    "cos" if args.len() == 1 => format!("Math.cos({})", args_js[0]),
+                    "tan" if args.len() == 1 => format!("Math.tan({})", args_js[0]),
+                    "atan2" if args.len() == 2 => format!("Math.atan2({}, {})", args_js[0], args_js[1]),
+                    "clamp" if args.len() == 3 => format!("Math.min(Math.max({}, {}), {})", args_js[0], args_js[1], args_js[2]),
+                    "lerp" if args.len() == 3 => format!("({} + ({} - {}) * {})", args_js[0], args_js[1], args_js[0], args_js[2]),
+
+                    // ── String operations ──
+                    "split" if args.len() == 2 => format!("{}.split({})", args_js[0], args_js[1]),
+                    "join" if args.len() == 2 => format!("{}.join({})", args_js[0], args_js[1]),
+                    "trim" if args.len() == 1 => format!("{}.trim()", args_js[0]),
+                    "upper" if args.len() == 1 => format!("{}.toUpperCase()", args_js[0]),
+                    "lower" if args.len() == 1 => format!("{}.toLowerCase()", args_js[0]),
+                    "replace" if args.len() == 3 => format!("{}.replace({}, {})", args_js[0], args_js[1], args_js[2]),
+                    "starts_with" if args.len() == 2 => format!("{}.startsWith({})", args_js[0], args_js[1]),
+                    "ends_with" if args.len() == 2 => format!("{}.endsWith({})", args_js[0], args_js[1]),
+                    "char_at" if args.len() == 2 => format!("{}.charAt({})", args_js[0], args_js[1]),
+                    "substring" if args.len() == 3 => format!("{}.substring({}, {})", args_js[0], args_js[1], args_js[2]),
+
+                    // ── Conversion ──
+                    "int" if args.len() == 1 => format!("parseInt({})", args_js[0]),
+                    "float" if args.len() == 1 => format!("parseFloat({})", args_js[0]),
+                    "string" if args.len() == 1 => format!("String({})", args_js[0]),
+                    "bool" if args.len() == 1 => format!("Boolean({})", args_js[0]),
+
+                    // ── Console / debug ──
+                    "log" => format!("console.log({})", args_js.join(", ")),
+                    "debug" => format!("console.debug({})", args_js.join(", ")),
+                    "warn" => format!("console.warn({})", args_js.join(", ")),
+
+                    // ── Timer ──
+                    "delay" if args.len() == 2 => format!("setTimeout(() => {{ {} }}, {})", args_js[0], args_js[1]),
+
+                    // ── Fallback: user-defined function ──
+                    _ => format!("{}({})", name, args_js.join(", ")),
+                }
             }
             Expr::If(cond, then_b, else_b) => {
                 let c = self.emit_expr(cond);
@@ -819,6 +912,17 @@ impl JsEmitter {
         format!("n{id}")
     }
 
+    /// Extract the root signal name from an expression.
+    /// `Ident("todos")` → "todos", `DotAccess(Ident("a"), "b")` → "a", fallback → "_arr"
+    fn get_signal_root_name(&self, expr: &Expr) -> String {
+        match expr {
+            Expr::Ident(name) => name.clone(),
+            Expr::DotAccess(base, _) => self.get_signal_root_name(base),
+            Expr::Index(base, _) => self.get_signal_root_name(base),
+            _ => "_arr".to_string(),
+        }
+    }
+
     fn emit_line(&mut self, line: &str) {
         for _ in 0..self.indent {
             self.output.push_str("  ");

compiler/ds-parser/src/ast.rs

@@ -28,6 +28,8 @@ pub enum Declaration {
     Stream(StreamDecl),
     /// `every 500 -> expr`
     Every(EveryDecl),
+    /// Top-level expression statement: `log("hello")`, `push(items, x)`
+    ExprStatement(Expr),
 }
 
 /// `let count = 0` or `let doubled = count * 2`

compiler/ds-parser/src/parser.rs

@@ -99,6 +99,11 @@ impl Parser {
             TokenKind::Constrain => self.parse_constrain_decl(),
             TokenKind::Stream => self.parse_stream_decl(),
             TokenKind::Every => self.parse_every_decl(),
+            // Expression statement: `log("hello")`, `push(items, x)`
+            TokenKind::Ident(_) => {
+                let expr = self.parse_expr()?;
+                Ok(Declaration::ExprStatement(expr))
+            }
             _ => Err(self.error(format!(
                 "expected declaration (let, view, effect, on, component, route, constrain, stream, every), got {:?}",
                 self.peek()

examples/builtins.ds

@@ -0,0 +1,43 @@
+-- DreamStack built-in functions test
+-- Tests array, math, string, and conversion builtins
+
+let items = [1, 2, 3, 4, 5]
+let name = "DreamStack"
+
+-- Array operations
+let count = len(items)
+let has_three = contains(items, 3)
+
+-- Math operations 
+let x = floor(3.7)
+let y = ceil(2.1)
+let small = min(10, 5)
+let big = max(10, 5)
+let clamped = clamp(15, 0, 10)
+let dist = sqrt(pow(3, 2) + pow(4, 2))
+
+-- String operations
+let upper_name = upper(name)
+let lower_name = lower(name)
+
+-- Console
+log("count:", count)
+log("distance:", dist)
+
+view main =
+  column [
+    text "Built-in Functions"
+    text "Items: {count}"
+    text "Has 3: {has_three}"
+    text "floor(3.7) = {x}"
+    text "ceil(2.1) = {y}" 
+    text "min(10,5) = {small}"
+    text "max(10,5) = {big}"
+    text "clamp(15,0,10) = {clamped}"
+    text "sqrt(3²+4²) = {dist}"
+    text "upper = {upper_name}"
+    text "lower = {lower_name}"
+    button "Push 6" { click: push(items, 6) }
+    button "Pop" { click: pop(items) }
+    text "Length: {len(items)}"
+  ]