Move if_def_fn into CorePackage.

src/packages/pkg_core.rs

@@ -4,9 +4,34 @@ use super::iter_basic::BasicIteratorPackage;
 use super::logic::LogicPackage;
 use super::string_basic::BasicStringPackage;
 
-use crate::def_package;
+use crate::fn_native::{CallableFunction, FnCallArgs};
+use crate::stdlib::{any::TypeId, iter::empty};
+use crate::{
+    calc_script_fn_hash, def_package, FnAccess, FnNamespace, ImmutableString, NativeCallContext,
+    INT,
+};
 
 def_package!(crate:CorePackage:"_Core_ package containing basic facilities.", lib, {
+    #[cfg(not(feature = "no_function"))]
+    {
+        let f = |ctx: NativeCallContext, args: &mut FnCallArgs| {
+            let num_params = args[1].clone().cast::<INT>();
+            let fn_name = args[0].as_str().unwrap();
+
+            Ok(if num_params < 0 {
+                false.into()
+            } else {
+                let hash_script = calc_script_fn_hash(empty(), fn_name, num_params as usize);
+                ctx.engine().has_override(ctx.mods, ctx.lib, 0, hash_script, true).into()
+            })
+        };
+
+        lib.set_fn("is_def_fn", FnNamespace::Global, FnAccess::Public,
+            Some(&["fn_name: &str", "num_params: INT"]),
+            &[TypeId::of::<ImmutableString>(), TypeId::of::<INT>()],
+            CallableFunction::from_method(Box::new(f)));
+    }
+
     ArithmeticPackage::init(lib);
     LogicPackage::init(lib);
     BasicStringPackage::init(lib);