diff --git a/nixide/src/expr/values/attrs.rs b/nixide/src/expr/values/attrs.rs
index 8008bf7..4baacd0 100644
--- a/nixide/src/expr/values/attrs.rs
+++ b/nixide/src/expr/values/attrs.rs
@@ -4,16 +4,16 @@ use std::ptr::{self, NonNull};
 use std::rc::Rc;
 
 use super::{NixThunk, NixValue, Value};
+use crate::NixError;
 use crate::errors::{ErrorContext, NixideError};
 use crate::stdext::{AsCPtr, CCharPtrExt};
 use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
 use crate::util::{panic_issue_call_failed, wrap};
-use crate::{EvalState, NixError};
 
 pub struct NixAttrs {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     len: u32,
 }
 
@@ -61,7 +61,7 @@ impl NixValue for NixAttrs {
         sys::ValueType_NIX_TYPE_ATTRS
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let len = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_attrs_size(ctx.as_ptr(), inner.as_ptr())
         })
@@ -88,7 +88,7 @@ impl NixAttrs {
             sys::nix_get_attr_byidx(
                 ctx.as_ptr(),
                 self.as_ptr(),
-                self.state.borrow().as_ptr(),
+                self.state.borrow_mut().as_ptr(),
                 index,
                 name_ptr,
             )
@@ -115,7 +115,7 @@ impl NixAttrs {
             sys::nix_get_attr_byidx_lazy(
                 ctx.as_ptr(),
                 self.as_ptr(),
-                self.state.borrow().as_ptr(),
+                self.state.borrow_mut().as_ptr(),
                 index,
                 name_ptr,
             )
@@ -140,7 +140,7 @@ impl NixAttrs {
             sys::nix_get_attr_name_byidx(
                 ctx.as_ptr(),
                 self.as_ptr(),
-                self.state.borrow().as_ptr(),
+                self.state.borrow_mut().as_ptr(),
                 index,
             )
         })
@@ -161,7 +161,7 @@ impl NixAttrs {
             sys::nix_get_attr_byname(
                 ctx.as_ptr(),
                 self.as_ptr(),
-                self.state.borrow().as_ptr(),
+                self.state.borrow_mut().as_ptr(),
                 name.as_ref()
                     .into_c_ptr()
                     .unwrap_or_else(|err| panic_issue_call_failed!("{}", err)),
@@ -187,7 +187,7 @@ impl NixAttrs {
             sys::nix_get_attr_byname_lazy(
                 ctx.as_ptr(),
                 self.as_ptr(),
-                self.state.borrow().as_ptr(),
+                self.state.borrow_mut().as_ptr(),
                 name.as_ref()
                     .into_c_ptr()
                     .unwrap_or_else(|err| panic_issue_call_failed!("{}", err)),
diff --git a/nixide/src/expr/values/bool.rs b/nixide/src/expr/values/bool.rs
index d604c94..01f5718 100644
--- a/nixide/src/expr/values/bool.rs
+++ b/nixide/src/expr/values/bool.rs
@@ -5,14 +5,14 @@ use std::rc::Rc;
 
 use super::NixValue;
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::panic_issue_call_failed;
 use crate::util::wrap;
 use crate::util::wrappers::AsInnerPtr;
-use crate::{EvalState, sys};
 
 pub struct NixBool {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: bool,
 }
 
@@ -60,7 +60,7 @@ impl NixValue for NixBool {
         sys::ValueType_NIX_TYPE_BOOL
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_bool(ctx.as_ptr(), inner.as_ptr())
         })
diff --git a/nixide/src/expr/values/float.rs b/nixide/src/expr/values/float.rs
index 1187821..b47569b 100644
--- a/nixide/src/expr/values/float.rs
+++ b/nixide/src/expr/values/float.rs
@@ -5,13 +5,13 @@ use std::rc::Rc;
 
 use super::NixValue;
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
 use crate::util::{panic_issue_call_failed, wrap};
-use crate::{EvalState, sys};
 
 pub struct NixFloat {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: f64,
 }
 
@@ -59,7 +59,7 @@ impl NixValue for NixFloat {
         sys::ValueType_NIX_TYPE_FLOAT
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_float(ctx.as_ptr(), inner.as_ptr())
         })
diff --git a/nixide/src/expr/values/function.rs b/nixide/src/expr/values/function.rs
index 5cf15a2..98827b1 100644
--- a/nixide/src/expr/values/function.rs
+++ b/nixide/src/expr/values/function.rs
@@ -3,16 +3,16 @@ use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
 use std::ptr::NonNull;
 use std::rc::Rc;
 
-use super::{NixThunk, NixValue, Value};
+use super::{NixValue, Value};
 use crate::errors::ErrorContext;
 use crate::stdext::SliceExt;
+use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
 use crate::util::{panic_issue_call_failed, wrap};
-use crate::{EvalState, sys};
 
 pub struct NixFunction {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: i64,
 }
 
@@ -60,7 +60,7 @@ impl NixValue for NixFunction {
         sys::ValueType_NIX_TYPE_FUNCTION
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_int(ctx.as_ptr(), inner.as_ptr())
         })
diff --git a/nixide/src/expr/values/int.rs b/nixide/src/expr/values/int.rs
index eccd7ef..4ddd147 100644
--- a/nixide/src/expr/values/int.rs
+++ b/nixide/src/expr/values/int.rs
@@ -5,13 +5,13 @@ use std::rc::Rc;
 
 use super::NixValue;
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
 use crate::util::{panic_issue_call_failed, wrap};
-use crate::{EvalState, sys};
 
 pub struct NixInt {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: i64,
 }
 
@@ -59,7 +59,7 @@ impl NixValue for NixInt {
         sys::ValueType_NIX_TYPE_INT
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_int(ctx.as_ptr(), inner.as_ptr())
         })
diff --git a/nixide/src/expr/values/list.rs b/nixide/src/expr/values/list.rs
index c062a87..fb82bc7 100644
--- a/nixide/src/expr/values/list.rs
+++ b/nixide/src/expr/values/list.rs
@@ -5,14 +5,13 @@ use std::rc::Rc;
 
 use super::{NixThunk, NixValue, Value};
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
 use crate::util::{panic_issue_call_failed, wrap};
-use crate::{EvalState, sys};
 
 pub struct NixList {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
-    value: i64,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
 }
 
 impl Drop for NixList {
@@ -59,17 +58,8 @@ impl NixValue for NixList {
         sys::ValueType_NIX_TYPE_LIST
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
-        let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
-            sys::nix_get_int(ctx.as_ptr(), inner.as_ptr())
-        })
-        .unwrap_or_else(|err| panic_issue_call_failed!("{}", err));
-
-        Self {
-            inner,
-            state,
-            value,
-        }
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
+        Self { inner, state }
     }
 }
 
diff --git a/nixide/src/expr/values/mod.rs b/nixide/src/expr/values/mod.rs
index 27fd5f6..6b1f459 100644
--- a/nixide/src/expr/values/mod.rs
+++ b/nixide/src/expr/values/mod.rs
@@ -45,7 +45,7 @@ pub trait NixValue: Drop + Display + Debug + AsInnerPtr<sys::nix_value> {
     fn type_id(&self) -> sys::ValueType;
 
     /// TODO
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self;
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self;
 }
 
 /// A Nix value
@@ -111,8 +111,18 @@ pub enum Value {
     // Failed(NixFailed),
 }
 
-impl From<(NonNull<sys::nix_value>, Rc<RefCell<EvalState>>)> for Value {
-    fn from(value: (NonNull<sys::nix_value>, Rc<RefCell<EvalState>>)) -> Self {
+impl
+    From<(
+        NonNull<sys::nix_value>,
+        Rc<RefCell<NonNull<sys::EvalState>>>,
+    )> for Value
+{
+    fn from(
+        value: (
+            NonNull<sys::nix_value>,
+            Rc<RefCell<NonNull<sys::EvalState>>>,
+        ),
+    ) -> Self {
         let (inner, state) = value;
 
         wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
@@ -125,6 +135,7 @@ impl From<(NonNull<sys::nix_value>, Rc<RefCell<EvalState>>)> for Value {
         })
         .unwrap_or_else(|err| panic_issue_call_failed!("{}", err));
 
+        #[allow(non_upper_case_globals)]
         match type_id {
             ValueType_NIX_TYPE_THUNK => Value::Thunk(<NixThunk as NixValue>::from(inner, state)),
             ValueType_NIX_TYPE_INT => Value::Int(<NixInt as NixValue>::from(inner, state)),
diff --git a/nixide/src/expr/values/null.rs b/nixide/src/expr/values/null.rs
index 7b92254..11440de 100644
--- a/nixide/src/expr/values/null.rs
+++ b/nixide/src/expr/values/null.rs
@@ -5,12 +5,12 @@ use std::rc::Rc;
 
 use super::NixValue;
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
-use crate::{EvalState, sys};
 
 pub struct NixNull {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
 }
 
 impl Drop for NixNull {
@@ -57,7 +57,7 @@ impl NixValue for NixNull {
         sys::ValueType_NIX_TYPE_NULL
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         Self { inner, state }
     }
 }
diff --git a/nixide/src/expr/values/path.rs b/nixide/src/expr/values/path.rs
index 9a7fdb2..b25dfa6 100644
--- a/nixide/src/expr/values/path.rs
+++ b/nixide/src/expr/values/path.rs
@@ -7,14 +7,14 @@ use std::rc::Rc;
 use super::NixValue;
 use crate::errors::ErrorContext;
 use crate::stdext::CCharPtrExt;
+use crate::sys;
 use crate::util::panic_issue_call_failed;
 use crate::util::wrap;
 use crate::util::wrappers::AsInnerPtr;
-use crate::{EvalState, sys};
 
 pub struct NixPath {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: PathBuf,
 }
 
@@ -62,7 +62,7 @@ impl NixValue for NixPath {
         sys::ValueType_NIX_TYPE_PATH
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_fn!(|ctx: &ErrorContext| unsafe {
             sys::nix_get_path_string(ctx.as_ptr(), inner.as_ptr())
         })
diff --git a/nixide/src/expr/values/string.rs b/nixide/src/expr/values/string.rs
index 9ee305a..93ec66d 100644
--- a/nixide/src/expr/values/string.rs
+++ b/nixide/src/expr/values/string.rs
@@ -6,14 +6,14 @@ use std::rc::Rc;
 
 use super::NixValue;
 use crate::errors::ErrorContext;
+use crate::sys;
 use crate::util::panic_issue_call_failed;
 use crate::util::wrap;
 use crate::util::wrappers::AsInnerPtr;
-use crate::{EvalState, sys};
 
 pub struct NixString {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
     value: String,
 }
 
@@ -61,7 +61,7 @@ impl NixValue for NixString {
         sys::ValueType_NIX_TYPE_STRING
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         let value = wrap::nix_string_callback!(
             |callback, userdata: *mut __UserData, ctx: &ErrorContext| unsafe {
                 sys::nix_get_string(
diff --git a/nixide/src/expr/values/thunk.rs b/nixide/src/expr/values/thunk.rs
index 5fbe0f7..6327623 100644
--- a/nixide/src/expr/values/thunk.rs
+++ b/nixide/src/expr/values/thunk.rs
@@ -4,7 +4,6 @@ use std::ptr::NonNull;
 use std::rc::Rc;
 
 use super::{NixValue, Value};
-use crate::EvalState;
 use crate::errors::ErrorContext;
 use crate::sys;
 use crate::util::wrappers::AsInnerPtr;
@@ -12,7 +11,7 @@ use crate::util::{panic_issue_call_failed, wrap};
 
 pub struct NixThunk {
     inner: NonNull<sys::nix_value>,
-    state: Rc<RefCell<EvalState>>,
+    state: Rc<RefCell<NonNull<sys::EvalState>>>,
 }
 
 impl Drop for NixThunk {
@@ -59,7 +58,7 @@ impl NixValue for NixThunk {
         sys::ValueType_NIX_TYPE_THUNK
     }
 
-    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<EvalState>>) -> Self {
+    fn from(inner: NonNull<sys::nix_value>, state: Rc<RefCell<NonNull<sys::EvalState>>>) -> Self {
         Self { inner, state }
     }
 }