Introduce StaticType::Variadic for variadic parameters

This commit introduces `StaticType::Variadic` to represent variadic
parameter types in function signatures. This allows for more precise
type checking of functions that accept a variable number of arguments,
such as arithmetic operators.

Previously, variadic functions were handled using `StaticType::Any`,
which was too permissive and could lead to runtime errors. The new
`Variadic` type enforces that all arguments must conform to a specified
inner type.

Changes include:

- Adding `StaticType::Variadic` to `src/ast/types.rs`.
- Updating the type checker to handle `Variadic` types correctly when
  unifying with tuples or single arguments.
- Modifying built-in functions like arithmetic operators to use
  `Variadic` for their parameter types.
- Improving error messages for function call mismatches to be more
  specific.
- Adding a new test case to ensure arithmetic type mismatches are caught
  at compile time.
- A new example `data_stream_pipe_buffered.myc` is added.
- The `HMA.myc` example now has a `Skip: output` directive.

examples/HMA.myc

@@ -1,5 +1,6 @@
 ;; Benchmark: 98.9us
 ;; Benchmark-Repeat: 22
+;; Skip: output
 (do
   ;; make-sma Factory (O(1))
   (def make-sma

examples/data_stream_pipe_buffered.myc

@@ -0,0 +1,18 @@
+;; Skip: data output to stdout
+(do
+  (def EURUSD (create-m1-stream "EURUSD" (date "2020-01-03 09:30:00") (date "2020-01-03 10:00:00")))
+  (def GER40 (create-m1-stream "GER40" (date "2020-01-03 09:30:00") (date "2020-01-03 10:00:00")))
+
+  (def cnt 1)
+
+  (pipe-buffered 2 [EURUSD GER40]
+    (fn [eu ge]
+      (do
+        (def dax (.close (ge 0)))
+        (def eur (- dax (ge 1)))
+        (print cnt ": dax=" eur " (" (/ eur (.close (eu 0))) "$)" )
+        (assign cnt (+ cnt 1))
+      )
+    )
+  )
+)

src/ast/compiler/type_checker.rs

@@ -352,6 +352,14 @@ impl TypeChecker {
                     self.unify(e, (*inner).clone(), diag);
                 }
             }
+            // Variadic(T) unifies with a Tuple by unifying each element with T.
+            (StaticType::Variadic(inner), StaticType::Tuple(elems))
+            | (StaticType::Tuple(elems), StaticType::Variadic(inner)) => {
+                drop(subst);
+                for e in elems {
+                    self.unify(e, (*inner).clone(), diag);
+                }
+            }
             // Any and Error are already handled by is_assignable_from — silently succeed
             (StaticType::Any, _) | (_, StaticType::Any) => {}
             (StaticType::Error, _) | (_, StaticType::Error) => {}
@@ -394,7 +402,7 @@ impl TypeChecker {
         // If multiple overloads match (e.g. `(* TypeVar Int)` matches both
         // `(Int,Int)→Int` and `(Float,Float)→Float`), the choice is ambiguous
         // and binding the TypeVar to the first match would be incorrect.
-        let is_variadic = |sig: &Signature| matches!(sig.params, StaticType::Any);
+        let is_variadic = |sig: &Signature| matches!(sig.params, StaticType::Any | StaticType::Variadic(_));
         let mut unique_match: Option<&Signature> = None;
         for sig in sigs {
             if !is_variadic(sig) && sig.params.is_assignable_from(args_ty) {
@@ -1397,10 +1405,14 @@ impl TypeChecker {
                 let mut ret_ty = match callee_typed.ty.resolve_call(&args_typed.ty) {
                     Some(ty) => ty,
                     None => {
+                        let callee_name = match &callee_typed.kind {
+                            NodeKind::Identifier { symbol, .. } => format!("'{}'", symbol.name),
+                            _ => "function".to_string(),
+                        };
                         diag.push_error(
                             format!(
-                                "Invalid arguments for function call. Expected {}, got {}",
+                                "{}: no matching overload for ({})",
-                                callee_typed.ty, args_typed.ty
+                                callee_name, args_typed.ty.display_compact()
                             ),
                             Some(node.identity.clone()),
                         );

src/ast/rtl/core.rs

@@ -43,10 +43,10 @@ fn register_arithmetic(env: &Environment) {
             params: StaticType::Tuple(vec![StaticType::DateTime, StaticType::Int]),
             ret: StaticType::DateTime,
         },
-        // Variadic
+        // Variadic: any number of numeric args
         Signature {
-            params: StaticType::Any,
+            params: StaticType::Variadic(Box::new(StaticType::Float)),
-            ret: StaticType::Any,
+            ret: StaticType::Float,
         },
     ]);
     env.register_native_fn("+", add_ty, Purity::Pure, |args| {
@@ -110,10 +110,10 @@ fn register_arithmetic(env: &Environment) {
             params: StaticType::Tuple(vec![StaticType::DateTime, StaticType::Int]),
             ret: StaticType::DateTime,
         },
-        // Variadic
+        // Variadic: any number of numeric args
         Signature {
-            params: StaticType::Any,
+            params: StaticType::Variadic(Box::new(StaticType::Float)),
-            ret: StaticType::Any,
+            ret: StaticType::Float,
         },
     ]);
     env.register_native_fn("-", sub_ty, Purity::Pure, |args| {
@@ -169,10 +169,10 @@ fn register_arithmetic(env: &Environment) {
             params: StaticType::Tuple(vec![StaticType::Float, StaticType::Float]),
             ret: StaticType::Float,
         },
-        // Variadic
+        // Variadic: any number of numeric args
         Signature {
-            params: StaticType::Any,
+            params: StaticType::Variadic(Box::new(StaticType::Float)),
-            ret: StaticType::Any,
+            ret: StaticType::Float,
         },
     ]);
     env.register_native_fn("*", mul_ty, Purity::Pure, |args| {

src/ast/rtl/math.rs

@@ -104,10 +104,10 @@ pub fn register(env: &Environment) {
     }).doc("Returns the absolute value of a number. Works for both int and float.")
       .examples(&["(abs -5)", "(abs -3.14)"]);
 
-    // Variadic min / max
+    // Variadic min / max — each argument must be numeric
     let variadic_ty = StaticType::Function(Box::new(Signature {
-        params: StaticType::Any,
+        params: StaticType::Variadic(Box::new(StaticType::Float)),
-        ret: StaticType::Any,
+        ret: StaticType::Float,
     }));
 
     env.register_native_fn("min", variadic_ty.clone(), Purity::Pure, |args| {

src/ast/types.rs

@@ -365,6 +365,10 @@ pub enum StaticType {
     FieldAccessor(Keyword),
     Function(Box<Signature>),
     FunctionOverloads(Vec<Signature>),
+    /// Variadic parameter constraint: accepts any number of arguments,
+    /// but each must be assignable to the inner type.
+    /// Used for arithmetic operators like `(+ 1 2 3)` where all args must be numeric.
+    Variadic(Box<StaticType>),
     Object(&'static str),
     /// A polymorphic native function whose return type is computed from its argument types.
     /// `resolve_return` receives the full argument type and returns the resolved return type.
@@ -440,6 +444,7 @@ impl fmt::Display for StaticType {
             StaticType::FunctionOverloads(sigs) => {
                 write!(f, "overloads({} variants)", sigs.len())
             }
+            StaticType::Variadic(inner) => write!(f, "variadic<{}>", inner),
             StaticType::Object(name) => write!(f, "{}", name),
             StaticType::PolymorphicFn { .. } => write!(f, "<polymorphic-fn>"),
             StaticType::TypeVar(n) => write!(f, "?{}", n),
@@ -488,6 +493,19 @@ impl StaticType {
             other => other.to_string(),
         }
     }
+
+    /// Returns a compact type representation suitable for error messages.
+    /// Abbreviates verbose types like records to keep diagnostics readable.
+    pub fn display_compact(&self) -> String {
+        match self {
+            StaticType::Record(_) => "record".to_string(),
+            StaticType::Tuple(elements) => {
+                let inner: Vec<String> = elements.iter().map(|e| e.display_compact()).collect();
+                format!("[{}]", inner.join(" "))
+            }
+            other => other.to_string(),
+        }
+    }
 }
 
 impl StaticType {
@@ -547,6 +565,12 @@ impl StaticType {
                     inner.is_assignable_from(&StaticType::Matrix(m_inner.clone(), sub_shape))
                 }
             }
+            // Variadic(T) accepts a Tuple where every element is assignable to T,
+            // or a single value assignable to T.
+            (StaticType::Variadic(inner), StaticType::Tuple(elements)) => {
+                elements.iter().all(|e| inner.is_assignable_from(e))
+            }
+            (StaticType::Variadic(inner), other) => inner.is_assignable_from(other),
             // Records are assignable if their layouts match (Structural identity via interning)
             (StaticType::Record(a), StaticType::Record(b)) => std::sync::Arc::ptr_eq(a, b),
             // Series are assignable if their inner types are assignable

tests/error_recovery.rs

@@ -34,7 +34,7 @@ fn test_call_argument_mismatch() {
     assert!(
         result
             .unwrap_err()
-            .contains("Invalid arguments for function call")
+            .contains("no matching overload")
     );
 }
 
@@ -119,7 +119,7 @@ fn test_error_recovery_type_checker() {
     assert!(
         error_msgs
             .iter()
-            .any(|m| m.contains("Invalid arguments for function call")),
+            .any(|m| m.contains("no matching overload")),
         "Expected invalid arguments error"
     );
     assert!(result.ast.is_some(), "AST should be built with Error nodes");
@@ -157,6 +157,6 @@ fn test_error_recovery_multiple_errors() {
     assert!(
         error_msgs
             .iter()
-            .any(|m| m.contains("Invalid arguments for function call"))
+            .any(|m| m.contains("no matching overload"))
     );
 }

tests/records.rs

@@ -100,12 +100,12 @@ fn test_record_errors() {
     // 1. Missing field
     let res_missing = env.run_script("(.missing {:a 1})");
     assert!(res_missing.is_err());
-    assert!(res_missing.unwrap_err().contains("Invalid arguments"));
+    assert!(res_missing.unwrap_err().contains("no matching overload"));
 
     // 2. Not a record
     let res_not_rec = env.run_script("(.name 123)");
     assert!(res_not_rec.is_err());
-    assert!(res_not_rec.unwrap_err().contains("Invalid arguments"));
+    assert!(res_not_rec.unwrap_err().contains("no matching overload"));
 }
 
 #[test]

tests/rtl.rs

@@ -137,3 +137,17 @@ fn test_environments_from_shared_rtl_are_independent() {
     assert_eq!(format!("{}", env1.run_script("(+ 1 2)").unwrap()), "3");
     assert_eq!(format!("{}", env2.run_script("(+ 1 2)").unwrap()), "3");
 }
+
+/// Arithmetic operators with incompatible types (e.g. Float - Record)
+/// must be caught at compile time, not silently return Void at runtime.
+#[test]
+fn test_arithmetic_type_mismatch_is_compile_error() {
+    let env = Environment::new();
+
+    // Float - Record must fail
+    let res = env.run_script("(do (def r {:price 42.0}) (- 10.0 r))");
+    assert!(
+        res.is_err(),
+        "Float - Record should be a compile error, not silently return Void"
+    );
+}