diff --git a/benches/eval_module.rs b/benches/eval_module.rs
index de7843c0..33941818 100644
--- a/benches/eval_module.rs
+++ b/benches/eval_module.rs
@@ -18,7 +18,7 @@ fn bench_eval_module(bench: &mut Bencher) {
 
     let ast = engine.compile(script).unwrap();
 
-    let module = Module::eval_ast_as_new(Default::default(), &ast, &engine).unwrap();
+    let module = Module::eval_ast_as_new(&mut Scope::new(), &ast, &engine).unwrap();
 
     engine.register_static_module("testing", module.into());
 
diff --git a/src/api/custom_syntax.rs b/src/api/custom_syntax.rs
index 3bb29821..c35c49af 100644
--- a/src/api/custom_syntax.rs
+++ b/src/api/custom_syntax.rs
@@ -151,7 +151,7 @@ impl Deref for Expression<'_> {
     }
 }
 
-impl EvalContext<'_, '_, '_, '_, '_, '_, '_, '_> {
+impl EvalContext<'_, '_, '_, '_, '_, '_, '_, '_, '_, '_> {
     /// Evaluate an [expression tree][Expression].
     ///
     /// # WARNING - Low Level API
diff --git a/src/eval/eval_context.rs b/src/eval/eval_context.rs
index 4629e185..7b0aa5dd 100644
--- a/src/eval/eval_context.rs
+++ b/src/eval/eval_context.rs
@@ -7,15 +7,15 @@ use std::prelude::v1::*;
 
 /// Context of a script evaluation process.
 #[derive(Debug)]
-pub struct EvalContext<'a, 'x, 'px, 'm, 's, 'b, 't, 'pt> {
+pub struct EvalContext<'a, 'x, 'px, 'm, 'pm, 's, 'ps, 'b, 't, 'pt> {
     /// The current [`Engine`].
     pub(crate) engine: &'a Engine,
     /// The current [`Scope`].
     pub(crate) scope: &'x mut Scope<'px>,
     /// The current [`GlobalRuntimeState`].
-    pub(crate) global: &'m mut GlobalRuntimeState,
+    pub(crate) global: &'m mut GlobalRuntimeState<'pm>,
     /// The current [evaluation state][EvalState].
-    pub(crate) state: &'s mut EvalState,
+    pub(crate) state: &'s mut EvalState<'ps>,
     /// The current stack of imported [modules][Module].
     pub(crate) lib: &'b [&'b Module],
     /// The current bound `this` pointer, if any.
@@ -24,7 +24,7 @@ pub struct EvalContext<'a, 'x, 'px, 'm, 's, 'b, 't, 'pt> {
     pub(crate) level: usize,
 }
 
-impl<'x, 'px, 'pt> EvalContext<'_, 'x, 'px, '_, '_, '_, '_, 'pt> {
+impl<'x, 'px, 'pt> EvalContext<'_, 'x, 'px, '_, '_, '_, '_, '_, '_, 'pt> {
     /// The current [`Engine`].
     #[inline(always)]
     #[must_use]
diff --git a/src/eval/eval_state.rs b/src/eval/eval_state.rs
index 3d15fb34..d0e9b2bc 100644
--- a/src/eval/eval_state.rs
+++ b/src/eval/eval_state.rs
@@ -3,13 +3,14 @@
 use crate::func::call::FnResolutionCache;
 use crate::StaticVec;
 use std::collections::BTreeMap;
+use std::marker::PhantomData;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
 /// _(internals)_ A type that holds all the current states of the [`Engine`].
 /// Exported under the `internals` feature only.
 #[derive(Debug, Clone)]
-pub struct EvalState {
+pub struct EvalState<'a> {
     /// Force a [`Scope`] search by name.
     ///
     /// Normally, access to variables are parsed with a relative offset into the [`Scope`] to avoid a lookup.
@@ -25,17 +26,20 @@ pub struct EvalState {
     pub scope_level: usize,
     /// Stack of function resolution caches.
     fn_resolution_caches: StaticVec<FnResolutionCache>,
+    /// Take care of the lifetime parameter
+    dummy: PhantomData<Option<&'a ()>>,
 }
 
-impl EvalState {
+impl EvalState<'_> {
     /// Create a new [`EvalState`].
     #[inline(always)]
     #[must_use]
-    pub const fn new() -> Self {
+    pub fn new() -> Self {
         Self {
             always_search_scope: false,
             scope_level: 0,
             fn_resolution_caches: StaticVec::new_const(),
+            dummy: PhantomData::default(),
         }
     }
     /// Get the number of function resolution cache(s) in the stack.
diff --git a/src/eval/global_state.rs b/src/eval/global_state.rs
index 0cf54632..b2dc0181 100644
--- a/src/eval/global_state.rs
+++ b/src/eval/global_state.rs
@@ -8,6 +8,7 @@ use std::{
     any::TypeId,
     fmt,
     iter::{FromIterator, Rev, Zip},
+    marker::PhantomData,
 };
 
 /// _(internals)_ A stack of imported [modules][Module] plus mutable global runtime states.
@@ -19,7 +20,7 @@ use std::{
 // Most usage will be looking up a particular key from the list and then getting the module that
 // corresponds to that key.
 #[derive(Clone)]
-pub struct GlobalRuntimeState {
+pub struct GlobalRuntimeState<'a> {
     /// Stack of module names.
     //
     // We cannot use Cow<str> here because `eval` may load a [module][Module] and
@@ -45,20 +46,22 @@ pub struct GlobalRuntimeState {
     #[cfg(not(feature = "no_function"))]
     constants:
         Option<Shared<crate::Locked<std::collections::BTreeMap<Identifier, crate::Dynamic>>>>,
+    /// Take care of the lifetime parameter.
+    dummy: PhantomData<&'a ()>,
 }
 
-impl Default for GlobalRuntimeState {
+impl Default for GlobalRuntimeState<'_> {
     #[inline(always)]
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl GlobalRuntimeState {
+impl GlobalRuntimeState<'_> {
     /// Create a new [`GlobalRuntimeState`].
     #[inline(always)]
     #[must_use]
-    pub const fn new() -> Self {
+    pub fn new() -> Self {
         Self {
             keys: StaticVec::new_const(),
             modules: StaticVec::new_const(),
@@ -72,6 +75,7 @@ impl GlobalRuntimeState {
             #[cfg(not(feature = "no_module"))]
             #[cfg(not(feature = "no_function"))]
             constants: None,
+            dummy: PhantomData::default(),
         }
     }
     /// Get the length of the stack of globally-imported [modules][Module].
@@ -230,7 +234,7 @@ impl GlobalRuntimeState {
     }
 }
 
-impl IntoIterator for GlobalRuntimeState {
+impl IntoIterator for GlobalRuntimeState<'_> {
     type Item = (Identifier, Shared<Module>);
     type IntoIter =
         Zip<Rev<smallvec::IntoIter<[Identifier; 3]>>, Rev<smallvec::IntoIter<[Shared<Module>; 3]>>>;
@@ -244,7 +248,7 @@ impl IntoIterator for GlobalRuntimeState {
     }
 }
 
-impl<K: Into<Identifier>, M: Into<Shared<Module>>> FromIterator<(K, M)> for GlobalRuntimeState {
+impl<K: Into<Identifier>, M: Into<Shared<Module>>> FromIterator<(K, M)> for GlobalRuntimeState<'_> {
     #[inline]
     fn from_iter<T: IntoIterator<Item = (K, M)>>(iter: T) -> Self {
         let mut lib = Self::new();
@@ -253,7 +257,7 @@ impl<K: Into<Identifier>, M: Into<Shared<Module>>> FromIterator<(K, M)> for Glob
     }
 }
 
-impl<K: Into<Identifier>, M: Into<Shared<Module>>> Extend<(K, M)> for GlobalRuntimeState {
+impl<K: Into<Identifier>, M: Into<Shared<Module>>> Extend<(K, M)> for GlobalRuntimeState<'_> {
     #[inline]
     fn extend<T: IntoIterator<Item = (K, M)>>(&mut self, iter: T) {
         iter.into_iter().for_each(|(k, m)| {
@@ -263,7 +267,7 @@ impl<K: Into<Identifier>, M: Into<Shared<Module>>> Extend<(K, M)> for GlobalRunt
     }
 }
 
-impl fmt::Debug for GlobalRuntimeState {
+impl fmt::Debug for GlobalRuntimeState<'_> {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let mut f = f.debug_struct("GlobalRuntimeState");
diff --git a/src/func/native.rs b/src/func/native.rs
index d3062816..17b93eac 100644
--- a/src/func/native.rs
+++ b/src/func/native.rs
@@ -65,7 +65,7 @@ pub struct NativeCallContext<'a> {
     /// Function source, if any.
     source: Option<&'a str>,
     /// The current [`GlobalRuntimeState`], if any.
-    global: Option<&'a GlobalRuntimeState>,
+    global: Option<&'a GlobalRuntimeState<'a>>,
     /// The current stack of loaded [modules][Module].
     lib: &'a [&'a Module],
     /// [Position] of the function call.
@@ -77,7 +77,7 @@ impl<'a, M: AsRef<[&'a Module]> + ?Sized, S: AsRef<str> + 'a + ?Sized>
         &'a Engine,
         &'a S,
         Option<&'a S>,
-        &'a GlobalRuntimeState,
+        &'a GlobalRuntimeState<'a>,
         &'a M,
         Position,
     )> for NativeCallContext<'a>
diff --git a/src/module/mod.rs b/src/module/mod.rs
index f8aa351b..7e79214e 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -750,7 +750,7 @@ impl Module {
                 let return_type = param_names.pop().unwrap();
                 (param_names, return_type)
             } else {
-                (param_names, Default::default())
+                (param_names, crate::SmartString::new_const())
             };
             f.metadata.params_info = param_names;
             f.metadata.return_type = return_type_name;
@@ -882,7 +882,7 @@ impl Module {
             let return_type = if names.len() > arg_types.as_ref().len() {
                 names.pop().unwrap()
             } else {
-                Default::default()
+                crate::SmartString::new_const()
             };
             names.shrink_to_fit();
             (names, return_type)