diff --git a/src/foreign/atom.rs b/src/foreign/atom.rs
index 4222c87..9f66dcb 100644
--- a/src/foreign/atom.rs
+++ b/src/foreign/atom.rs
@@ -20,12 +20,6 @@ pub struct AtomicReturn {
   /// [Atomic::run]
   pub inert: bool,
 }
-impl AtomicReturn {
-  /// Wrap an inert atomic for delivery to the supervisor
-  pub fn from_data<D: Atomic>(d: D, c: Context) -> Self {
-    AtomicReturn { clause: d.atom_cls(), gas: c.gas, inert: false }
-  }
-}
 
 /// Returned by [Atomic::run]
 pub type AtomicResult = Result<AtomicReturn, RuntimeError>;
@@ -40,15 +34,17 @@ where
   ///
   /// This function should be implemented in exactly one way:
   ///
+  /// ```ignore
+  /// fn as_any(self: Box<Self>) -> Box<dyn Any> { self }
   /// ```
-  /// fn as_any(&self) -> &dyn Any { self }
-  /// ```
-  fn as_any(&self) -> &dyn Any;
+  fn as_any(self: Box<Self>) -> Box<dyn Any>;
+  /// See [Atomic::as_any], exactly the same but for references
+  fn as_any_ref(&self) -> &dyn Any;
 
   /// Attempt to normalize this value. If it wraps a value, this should report
   /// inert. If it wraps a computation, it should execute one logical step of
   /// the computation and return a structure representing the ntext.
-  fn run(&self, ctx: Context) -> AtomicResult;
+  fn run(self: Box<Self>, ctx: Context) -> AtomicResult;
 
   /// Wrap the atom in a clause to be placed in an [AtomicResult].
   fn atom_cls(self) -> Clause
@@ -83,17 +79,20 @@ impl Atom {
   /// Get the contained data
   pub fn data(&self) -> &dyn Atomic { self.0.as_ref() as &dyn Atomic }
   /// Attempt to downcast contained data to a specific type
-  pub fn try_cast<T: Atomic>(&self) -> Option<&T> {
-    self.data().as_any().downcast_ref()
+  pub fn try_cast<T: Atomic>(self) -> Result<T, Self> {
+    match self.0.as_any_ref().is::<T>() {
+      true => Ok(*self.0.as_any().downcast().expect("checked just above")),
+      false => Err(self),
+    }
   }
   /// Test the type of the contained data without downcasting
-  pub fn is<T: 'static>(&self) -> bool { self.data().as_any().is::<T>() }
+  pub fn is<T: 'static>(&self) -> bool { self.data().as_any_ref().is::<T>() }
   /// Downcast contained data, panic if it isn't the specified type
-  pub fn cast<T: 'static>(&self) -> &T {
-    self.data().as_any().downcast_ref().expect("Type mismatch on Atom::cast")
+  pub fn cast<T: 'static>(self) -> T {
+    *self.0.as_any().downcast().expect("Type mismatch on Atom::cast")
   }
   /// Normalize the contained data
-  pub fn run(&self, ctx: Context) -> AtomicResult { self.0.run(ctx) }
+  pub fn run(self, ctx: Context) -> AtomicResult { self.0.run(ctx) }
 }
 
 impl Clone for Atom {
diff --git a/src/foreign/cps_box.rs b/src/foreign/cps_box.rs
index a6eb702..0ff4c6c 100644
--- a/src/foreign/cps_box.rs
+++ b/src/foreign/cps_box.rs
@@ -35,7 +35,7 @@ impl<T: CPSPayload> CPSFn<T> {
 }
 impl<T: CPSPayload> ExternFn for CPSFn<T> {
   fn name(&self) -> &str { "CPS function without argument" }
-  fn apply(&self, arg: ExprInst, _ctx: Context) -> XfnResult {
+  fn apply(self: Box<Self>, arg: ExprInst, _ctx: Context) -> XfnResult {
     let payload = self.payload.clone();
     let continuations = pushed_ref(&self.continuations, arg);
     if self.argc == 1 {
@@ -68,26 +68,27 @@ impl<T: CPSPayload> CPSBox<T> {
     )
   }
   /// Unpack the wrapped command and the continuation
-  pub fn unpack1(&self) -> (&T, &ExprInst) {
+  pub fn unpack1(self) -> (T, ExprInst) {
     self.assert_count(1);
-    (&self.payload, &self.continuations[0])
+    let [cont]: [ExprInst; 1] =
+      self.continuations.try_into().expect("size checked");
+    (self.payload, cont)
   }
   /// Unpack the wrapped command and 2 continuations (usually an async and a
   /// sync)
-  pub fn unpack2(&self) -> (&T, &ExprInst, &ExprInst) {
+  pub fn unpack2(self) -> (T, ExprInst, ExprInst) {
     self.assert_count(2);
-    (&self.payload, &self.continuations[0], &self.continuations[1])
+    let [c1, c2]: [ExprInst; 2] =
+      self.continuations.try_into().expect("size checked");
+    (self.payload, c1, c2)
   }
   /// Unpack the wrapped command and 3 continuations (usually an async success,
   /// an async fail and a sync)
-  pub fn unpack3(&self) -> (&T, &ExprInst, &ExprInst, &ExprInst) {
+  pub fn unpack3(self) -> (T, ExprInst, ExprInst, ExprInst) {
     self.assert_count(3);
-    (
-      &self.payload,
-      &self.continuations[0],
-      &self.continuations[1],
-      &self.continuations[2],
-    )
+    let [c1, c2, c3]: [ExprInst; 3] =
+      self.continuations.try_into().expect("size checked");
+    (self.payload, c1, c2, c3)
   }
 }
 
diff --git a/src/foreign/extern_fn.rs b/src/foreign/extern_fn.rs
index d7a8700..fd4f6a0 100644
--- a/src/foreign/extern_fn.rs
+++ b/src/foreign/extern_fn.rs
@@ -39,7 +39,7 @@ pub trait ExternFn: DynClone {
   /// Display name of the function
   fn name(&self) -> &str;
   /// Combine the function with an argument to produce a new clause
-  fn apply(&self, arg: ExprInst, ctx: Context) -> XfnResult;
+  fn apply(self: Box<Self>, arg: ExprInst, ctx: Context) -> XfnResult;
   /// Hash the name to get a somewhat unique hash.
   fn hash(&self, mut state: &mut dyn std::hash::Hasher) {
     self.name().hash(&mut state)
diff --git a/src/foreign/inert.rs b/src/foreign/inert.rs
index 38ebbec..c425421 100644
--- a/src/foreign/inert.rs
+++ b/src/foreign/inert.rs
@@ -6,10 +6,11 @@ use super::{AtomicResult, AtomicReturn, ExternError};
 #[allow(unused)] // for doc
 use crate::define_fn;
 use crate::foreign::Atomic;
-use crate::interpreted::{ExprInst, TryFromExprInst};
+use crate::interpreted::{Clause, Expr, ExprInst, TryFromExprInst};
 use crate::interpreter::Context;
-use crate::systems::cast_exprinst::with_atomic;
+use crate::systems::AssertionError;
 use crate::utils::ddispatch::{Request, Responder};
+use crate::Primitive;
 
 /// A proxy trait that implements [Atomic] for blobs of data in Rust code that
 /// cannot be processed and always report inert. Since these are expected to be
@@ -28,19 +29,23 @@ impl<T: InertAtomic> Responder for T {
   fn respond(&self, request: Request) { self.respond(request) }
 }
 impl<T: InertAtomic> Atomic for T {
-  fn as_any(&self) -> &dyn Any { self }
+  fn as_any(self: Box<Self>) -> Box<dyn Any> { self }
+  fn as_any_ref(&self) -> &dyn Any { self }
 
-  fn run(&self, ctx: Context) -> AtomicResult {
-    Ok(AtomicReturn {
-      clause: self.clone().atom_cls(),
-      gas: ctx.gas,
-      inert: true,
-    })
+  fn run(self: Box<Self>, ctx: Context) -> AtomicResult {
+    Ok(AtomicReturn { gas: ctx.gas, inert: true, clause: self.atom_cls() })
   }
 }
 
 impl<T: InertAtomic> TryFromExprInst for T {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_atomic(exi, Self::type_str(), |a: &T| Ok(a.clone()))
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    let Expr { clause, location } = exi.expr_val();
+    match clause {
+      Clause::P(Primitive::Atom(a)) => match a.0.as_any().downcast() {
+        Ok(t) => Ok(*t),
+        Err(_) => AssertionError::fail(location, Self::type_str()),
+      },
+      _ => AssertionError::fail(location, "atom"),
+    }
   }
 }
diff --git a/src/foreign_macros/atomic_impl.rs b/src/foreign_macros/atomic_impl.rs
index 6e69840..c116f77 100644
--- a/src/foreign_macros/atomic_impl.rs
+++ b/src/foreign_macros/atomic_impl.rs
@@ -41,8 +41,9 @@ use crate::Primitive;
 /// ```
 /// use orchidlang::{Literal};
 /// use orchidlang::interpreted::{ExprInst, Clause};
-/// use orchidlang::systems::cast_exprinst::with_lit;
+/// use orchidlang::systems::cast_exprinst::get_literal;
 /// use orchidlang::{atomic_impl, atomic_redirect, externfn_impl};
+/// use orchidlang::ddispatch::Responder;
 ///
 /// /// Convert a literal to a string using Rust's conversions for floats, chars and
 /// /// uints respectively
@@ -50,65 +51,67 @@ use crate::Primitive;
 /// struct ToString;
 ///
 /// externfn_impl!{
-///   ToString, |_: &Self, expr_inst: ExprInst|{
-///     Ok(InternalToString {
-///       expr_inst
-///     })
+///   ToString, |_: Self, expr_inst: ExprInst|{
+///     Ok(InternalToString { expr_inst })
 ///   }
 /// }
 /// #[derive(std::fmt::Debug,Clone)]
 /// struct InternalToString {
 ///   expr_inst: ExprInst,
 /// }
+/// impl Responder for InternalToString {}
 /// atomic_redirect!(InternalToString, expr_inst);
-/// atomic_impl!(InternalToString, |Self { expr_inst }: &Self, _|{
-///   with_lit(expr_inst, |l| Ok(match l {
-///     Literal::Uint(i) => Literal::Str(i.to_string().into()),
-///     Literal::Num(n) => Literal::Str(n.to_string().into()),
-///     s@Literal::Str(_) => s.clone(),
-///   })).map(Clause::from)
+/// atomic_impl!(InternalToString, |Self { expr_inst }: Self, _|{
+///   Ok(match get_literal(expr_inst)?.0 {
+///     Literal::Uint(i) => Clause::from(Literal::Str(i.to_string().into())),
+///     Literal::Num(n) => Clause::from(Literal::Str(n.to_string().into())),
+///     s@Literal::Str(_) => Clause::from(s),
+///   })
 /// });
 /// ```
 #[macro_export]
 macro_rules! atomic_impl {
   ($typ:ident) => {
-    $crate::atomic_impl! {$typ, |this: &Self, _: $crate::interpreter::Context| {
+    $crate::atomic_impl! {$typ, |this: Self, _: $crate::interpreter::Context| {
       use $crate::foreign::ExternFn;
-      Ok(this.clone().xfn_cls())
+      Ok(this.xfn_cls())
     }}
   };
   ($typ:ident, $next_phase:expr) => {
     impl $crate::foreign::Atomic for $typ {
-      fn as_any(&self) -> &dyn std::any::Any { self }
+      fn as_any(self: Box<Self>) -> Box<dyn std::any::Any> { self }
+      fn as_any_ref(&self) -> &dyn std::any::Any { self }
 
       fn run(
-        &self,
+        self: Box<Self>,
         ctx: $crate::interpreter::Context,
       ) -> $crate::foreign::AtomicResult {
         // extract the expression
+        let mut this = *self;
         let expr =
-          <Self as AsRef<$crate::interpreted::ExprInst>>::as_ref(self).clone();
+          <Self as AsMut<$crate::interpreted::ExprInst>>::as_mut(&mut this);
         // run the expression
-        let ret = $crate::interpreter::run(expr, ctx.clone())?;
-        let $crate::interpreter::Return { gas, state, inert } = ret;
-        // rebuild the atomic
-        let next_self = <Self as From<(
-          &Self,
-          $crate::interpreted::ExprInst,
-        )>>::from((self, state));
+        let (gas, inert) =
+          $crate::take_with_output(
+            expr,
+            |expr| match $crate::interpreter::run(expr, ctx.clone()) {
+              Ok(ret) => (ret.state, Ok((ret.gas, ret.inert))),
+              Err(e) => ($crate::interpreted::Clause::Bottom.wrap(), Err(e)),
+            },
+          )?;
         // branch off or wrap up
         let clause = if inert {
           let closure = $next_phase;
           let res: Result<
             $crate::interpreted::Clause,
             std::rc::Rc<dyn $crate::foreign::ExternError>,
-          > = closure(&next_self, ctx);
+          > = closure(this, ctx);
           match res {
             Ok(r) => r,
             Err(e) => return Err($crate::interpreter::RuntimeError::Extern(e)),
           }
         } else {
-          next_self.atom_cls()
+          this.atom_cls()
         };
         // package and return
         Ok($crate::foreign::AtomicReturn { clause, gas, inert: false })
diff --git a/src/foreign_macros/atomic_redirect.rs b/src/foreign_macros/atomic_redirect.rs
index 70c7db0..2ae4bd2 100644
--- a/src/foreign_macros/atomic_redirect.rs
+++ b/src/foreign_macros/atomic_redirect.rs
@@ -6,23 +6,14 @@ use crate::atomic_impl;
 #[macro_export]
 macro_rules! atomic_redirect {
   ($typ:ident) => {
-    impl AsRef<$crate::foreign::RcExpr> for $typ {
-      fn as_ref(&self) -> &Clause { &self.0 }
-    }
-    impl From<(&Self, $crate::foreign::RcExpr)> for $typ {
-      fn from((old, clause): (&Self, Clause)) -> Self {
-        Self { 0: clause, ..old.clone() }
-      }
+    impl AsMut<$crate::interpreted::ExprInst> for $typ {
+      fn as_mut(&mut self) -> &mut $crate::interpreted::ExprInst { &mut self.0 }
     }
   };
   ($typ:ident, $field:ident) => {
-    impl AsRef<$crate::interpreted::ExprInst> for $typ {
-      fn as_ref(&self) -> &$crate::interpreted::ExprInst { &self.$field }
-    }
-    impl From<(&Self, $crate::interpreted::ExprInst)> for $typ {
-      #[allow(clippy::needless_update)]
-      fn from((old, $field): (&Self, $crate::interpreted::ExprInst)) -> Self {
-        Self { $field, ..old.clone() }
+    impl AsMut<$crate::interpreted::ExprInst> for $typ {
+      fn as_mut(&mut self) -> &mut $crate::interpreted::ExprInst {
+        &mut self.$field
       }
     }
   };
diff --git a/src/foreign_macros/define_fn.rs b/src/foreign_macros/define_fn.rs
index 8c05dc6..bf6e424 100644
--- a/src/foreign_macros/define_fn.rs
+++ b/src/foreign_macros/define_fn.rs
@@ -1,7 +1,7 @@
 #[allow(unused)] // for doc
 use crate::foreign::ExternFn;
 #[allow(unused)] // for doc
-use crate::interpreted::ExprInst;
+use crate::interpreted::{ExprInst, TryFromExprInst};
 #[allow(unused)] // for doc
 use crate::write_fn_step;
 
@@ -27,9 +27,7 @@ use crate::write_fn_step;
 /// `Rc<dyn ExternError>`.
 ///
 /// To avoid typing the same expression a lot, the conversion is optional.
-/// If it is omitted, the field is initialized with a [TryInto::try_into] call
-/// from `&ExprInst` to the target type. In this case, the error is
-/// short-circuited using `?` so conversions through `FromResidual` are allowed.
+/// If it is omitted, the field is initialized using [TryFromExprInst].
 /// The optional syntax starts with `as`.
 ///
 /// If all conversions are omitted, the alias definition (`expr=$ident in`) has
@@ -41,14 +39,13 @@ use crate::write_fn_step;
 ///
 /// ```
 /// use orchidlang::interpreted::Clause;
-/// use orchidlang::systems::cast_exprinst::with_str;
 /// use orchidlang::{define_fn, Literal, OrcString, Primitive};
 ///
 /// define_fn! {expr=x in
 ///   /// Append a string to another
 ///   pub Concatenate {
-///     a: OrcString as with_str(x, |s| Ok(s.clone())),
-///     b: OrcString as with_str(x, |s| Ok(s.clone()))
+///     a: OrcString as x.downcast(),
+///     b: OrcString
 ///   } => {
 ///     Ok(Clause::P(Primitive::Literal(Literal::Str(
 ///       OrcString::from(a.get_string() + &b)
@@ -61,23 +58,26 @@ use crate::write_fn_step;
 ///
 /// ```
 /// use orchidlang::interpreted::Clause;
-/// use orchidlang::systems::cast_exprinst::with_lit;
+/// use orchidlang::systems::cast_exprinst::get_literal;
 /// use orchidlang::{define_fn, Literal};
 ///
 /// define_fn! {
 ///   /// Convert a literal to a string using Rust's conversions for floats,
 ///   /// chars and uints respectively
-///   ToString = |x| with_lit(x, |l| Ok(match l {
-///     Literal::Uint(i) => Literal::Str(i.to_string().into()),
-///     Literal::Num(n) => Literal::Str(n.to_string().into()),
-///     s@Literal::Str(_) => s.clone(),
-///   })).map(Clause::from)
+///   ToString = |x| Ok(match get_literal(x)?.0 {
+///     Literal::Uint(i) => Clause::from(Literal::Str(i.to_string().into())),
+///     Literal::Num(n) => Clause::from(Literal::Str(n.to_string().into())),
+///     s@Literal::Str(_) => Clause::from(s),
+///   })
 /// }
 /// ```
 #[macro_export]
 macro_rules! define_fn {
   // Unary function entry
-  ($( #[ $attr:meta ] )* $qual:vis $name:ident = |$x:ident| $body:expr) => {
+  (
+    $( #[ $attr:meta ] )* $qual:vis $name:ident = |$x:ident| $body:expr
+    $(; $( $next:tt )+ )?
+  ) => {
     paste::paste!{
       $crate::write_fn_step!(
         $( #[ $attr ] )* $qual $name
@@ -89,21 +89,28 @@ macro_rules! define_fn {
         {}
         out = expr => Ok(expr);
         {
-          let lambda = |$x: &$crate::interpreted::ExprInst| $body;
+          let lambda = |$x: $crate::interpreted::ExprInst| $body;
           lambda(out)
         }
       );
     }
+
+    $( $crate::define_fn!{ $( $next )+ } )?
   };
   // xname is optional only if every conversion is implicit
-  ($( #[ $attr:meta ] )* $qual:vis $name:ident {
-    $( $arg:ident: $typ:ty ),+  $(,)?
-  } => $body:expr) => {
+  (
+    $( #[ $attr:meta ] )* $qual:vis $name:ident {
+      $( $arg:ident: $typ:ty ),+  $(,)?
+    } => $body:expr
+    $(; $( $next:tt )+ )?
+  ) => {
     $crate::define_fn!{expr=expr in
       $( #[ $attr ] )* $qual $name {
         $( $arg: $typ ),*
       } => $body
     }
+
+    $( $crate::define_fn!{ $( $next )+ } )?
   };
   // multi-parameter function entry
   (expr=$xname:ident in
@@ -112,24 +119,29 @@ macro_rules! define_fn {
       $arg0:ident: $typ0:ty $( as $parse0:expr )?
       $(, $arg:ident: $typ:ty $( as $parse:expr )? )* $(,)?
     } => $body:expr
-  ) => {paste::paste!{
-    // Generate initial state
-    $crate::write_fn_step!(
-      $( #[ $attr ] )* $qual $name
-      >
-      [< Internal $name >]
-    );
-    // Enter loop to generate intermediate states
-    $crate::define_fn!(@MIDDLE $xname [< Internal $name >] ($body)
-      ()
-      (
-        ( $arg0: $typ0 $( as $parse0)? )
-        $(
-          ( $arg: $typ $( as $parse)? )
-        )*
-      )
-    );
-  }};
+    $(; $( $next:tt )+ )?
+  ) => {
+    paste::paste!{
+      // Generate initial state
+      $crate::write_fn_step!(
+        $( #[ $attr ] )* $qual $name
+        >
+        [< Internal $name >]
+      );
+      // Enter loop to generate intermediate states
+      $crate::define_fn!(@MIDDLE $xname [< Internal $name >] ($body)
+        ()
+        (
+          ( $arg0: $typ0 $( as $parse0)? )
+          $(
+            ( $arg: $typ $( as $parse)? )
+          )*
+        )
+      );
+    }
+
+    $( $crate::define_fn!{ expr = $xname in $( $next )+ } )?
+  };
   // Recursive case
   (@MIDDLE $xname:ident $name:ident ($body:expr)
     // fields that should be included in this struct
diff --git a/src/foreign_macros/externfn_impl.rs b/src/foreign_macros/externfn_impl.rs
index bd7636c..e14fb22 100644
--- a/src/foreign_macros/externfn_impl.rs
+++ b/src/foreign_macros/externfn_impl.rs
@@ -27,12 +27,12 @@ macro_rules! externfn_impl {
     impl $crate::foreign::ExternFn for $typ {
       fn name(&self) -> &str { stringify!($typ) }
       fn apply(
-        &self,
+        self: Box<Self>,
         arg: $crate::interpreted::ExprInst,
         _ctx: $crate::interpreter::Context,
       ) -> $crate::foreign::XfnResult {
         let closure = $next_atomic;
-        match closure(self, arg) {
+        match closure(*self, arg) {
           // ? casts the result but we want to strictly forward it
           Ok(r) => Ok($crate::interpreted::Clause::P($crate::Primitive::Atom(
             $crate::foreign::Atom::new(r),
diff --git a/src/foreign_macros/write_fn_step.rs b/src/foreign_macros/write_fn_step.rs
index 5d1bdcd..628c7c7 100644
--- a/src/foreign_macros/write_fn_step.rs
+++ b/src/foreign_macros/write_fn_step.rs
@@ -23,7 +23,6 @@ use crate::interpreted::ExprInst;
 ///
 /// use orchidlang::{write_fn_step, Literal, Primitive, OrcString};
 /// use orchidlang::interpreted::Clause;
-/// use orchidlang::systems::cast_exprinst::{with_str, with_uint};
 /// use orchidlang::systems::RuntimeError;
 ///
 /// // Initial state
@@ -31,14 +30,14 @@ use crate::interpreted::ExprInst;
 /// // Middle state
 /// write_fn_step!(
 ///   CharAt1 {}
-///   CharAt0 where s: OrcString = x => with_str(x, |s| Ok(s.clone()));
+///   CharAt0 where s: OrcString = x => x.downcast::<OrcString>();
 /// );
 /// // Exit state
 /// write_fn_step!(
 ///   CharAt0 { s: OrcString }
-///   i = x => with_uint(x, Ok);
+///   i = x => x.downcast::<u64>();
 ///   {
-///     if let Some(c) = s.graphemes(true).nth(*i as usize) {
+///     if let Some(c) = s.graphemes(true).nth(i as usize) {
 ///       Ok(Literal::Str(OrcString::from(c.to_string())).into())
 ///     } else {
 ///       RuntimeError::fail(
@@ -88,7 +87,7 @@ macro_rules! write_fn_step {
     $quant struct $name;
     $crate::externfn_impl!{
       $name,
-      |_: &Self, expr_inst: $crate::interpreted::ExprInst| {
+      |_: Self, expr_inst: $crate::interpreted::ExprInst| {
         Ok($next{ expr_inst })
       }
     }
@@ -107,14 +106,14 @@ macro_rules! write_fn_step {
       $( $arg: $typ, )*
       expr_inst: $crate::interpreted::ExprInst,
     }
-    impl $crate::utils::ddispatch::Responder for $name {}
+    impl $crate::ddispatch::Responder for $name {}
     $crate::atomic_redirect!($name, expr_inst);
     $crate::atomic_impl!($name);
     $crate::externfn_impl!(
       $name,
-      |this: &Self, expr_inst: $crate::interpreted::ExprInst| {
+      |this: Self, expr_inst: $crate::interpreted::ExprInst| {
         let $added $( :$added_typ )? =
-          $crate::write_fn_step!(@CONV &this.expr_inst $(, $xname $extract )?);
+          $crate::write_fn_step!(@CONV this.expr_inst $(, $xname $extract )?);
         Ok($next{
           $( $arg: this.$arg.clone(), )*
           $added, expr_inst
@@ -137,13 +136,12 @@ macro_rules! write_fn_step {
       expr_inst: $crate::interpreted::ExprInst,
     }
     $crate::atomic_redirect!($name, expr_inst);
-    impl $crate::utils::ddispatch::Responder for $name {}
+    impl $crate::ddispatch::Responder for $name {}
     $crate::atomic_impl!(
       $name,
-      |Self{ $($arg, )* expr_inst }: &Self, _| {
-        let added $(: $added_typ )? =
+      |Self{ $($arg, )* expr_inst }, _| {
+        let $added $(: $added_typ )? =
           $crate::write_fn_step!(@CONV expr_inst $(, $xname $extract )?);
-        let $added = &added;
         $process
       }
     );
diff --git a/src/interpreter/apply.rs b/src/interpreter/apply.rs
index bb2c95f..041cfae 100644
--- a/src/interpreter/apply.rs
+++ b/src/interpreter/apply.rs
@@ -13,17 +13,14 @@ use crate::utils::Side;
 fn map_at<E>(
   path: &[Side],
   source: ExprInst,
-  mapper: &mut impl FnMut(&Clause) -> Result<Clause, E>,
+  mapper: &mut impl FnMut(Clause) -> Result<Clause, E>,
 ) -> Result<ExprInst, E> {
   source
     .try_update(|value, _loc| {
       // Pass right through lambdas
       if let Clause::Lambda { args, body } = value {
         return Ok((
-          Clause::Lambda {
-            args: args.clone(),
-            body: map_at(path, body.clone(), mapper)?,
-          },
+          Clause::Lambda { args, body: map_at(path, body, mapper)? },
           (),
         ));
       }
@@ -37,14 +34,8 @@ fn map_at<E>(
       if let Clause::Apply { f, x } = value {
         return Ok((
           match head {
-            Side::Left => Clause::Apply {
-              f: map_at(tail, f.clone(), mapper)?,
-              x: x.clone(),
-            },
-            Side::Right => Clause::Apply {
-              f: f.clone(),
-              x: map_at(tail, x.clone(), mapper)?,
-            },
+            Side::Left => Clause::Apply { f: map_at(tail, f, mapper)?, x },
+            Side::Right => Clause::Apply { f, x: map_at(tail, x, mapper)? },
           },
           (),
         ));
@@ -63,8 +54,8 @@ fn substitute(paths: &PathSet, value: Clause, body: ExprInst) -> ExprInst {
     match (checkpoint, next) {
       (Clause::Lambda { .. }, _) => unreachable!("Handled by map_at"),
       (Clause::Apply { f, x }, Some((left, right))) => Ok(Clause::Apply {
-        f: substitute(left, value.clone(), f.clone()),
-        x: substitute(right, value.clone(), x.clone()),
+        f: substitute(left, value.clone(), f),
+        x: substitute(right, value.clone(), x),
       }),
       (Clause::LambdaArg, None) => Ok(value.clone()),
       (_, None) => {
@@ -91,20 +82,19 @@ pub fn apply(
       Ok((clause, (ctx.gas.map(|g| g - 1), false)))
     },
     Clause::Lambda { args, body } => Ok(if let Some(args) = args {
-      let x_cls = x.expr().clause.clone();
-      let new_xpr_inst = substitute(args, x_cls, body.clone());
-      let new_xpr = new_xpr_inst.expr();
+      let x_cls = x.expr_val().clause;
+      let result = substitute(&args, x_cls, body);
       // cost of substitution
       // XXX: should this be the number of occurrences instead?
-      (new_xpr.clause.clone(), (ctx.gas.map(|x| x - 1), false))
+      (result.expr_val().clause, (ctx.gas.map(|x| x - 1), false))
     } else {
-      (body.expr().clause.clone(), (ctx.gas, false))
+      (body.expr_val().clause, (ctx.gas, false))
     }),
     Clause::Constant(name) =>
-      if let Some(sym) = ctx.symbols.get(name) {
+      if let Some(sym) = ctx.symbols.get(&name) {
         Ok((Clause::Apply { f: sym.clone(), x }, (ctx.gas, false)))
       } else {
-        Err(RuntimeError::MissingSymbol(name.clone(), loc.clone()))
+        Err(RuntimeError::MissingSymbol(name.clone(), loc))
       },
     Clause::P(Primitive::Atom(atom)) => {
       // take a step in expanding atom
@@ -113,11 +103,11 @@ pub fn apply(
     },
     Clause::Apply { f: fun, x: arg } => {
       // take a step in resolving pre-function
-      let ret = apply(fun.clone(), arg.clone(), ctx.clone())?;
+      let ret = apply(fun, arg, ctx.clone())?;
       let Return { state, inert, gas } = ret;
       Ok((Clause::Apply { f: state, x }, (gas, inert)))
     },
-    _ => Err(RuntimeError::NonFunctionApplication(f.clone())),
+    _ => Err(RuntimeError::NonFunctionApplication(loc)),
   })?;
   Ok(Return { state, gas, inert })
 }
diff --git a/src/interpreter/error.rs b/src/interpreter/error.rs
index 3834231..ede768b 100644
--- a/src/interpreter/error.rs
+++ b/src/interpreter/error.rs
@@ -2,7 +2,6 @@ use std::fmt::Display;
 use std::rc::Rc;
 
 use crate::foreign::ExternError;
-use crate::representations::interpreted::ExprInst;
 use crate::{Location, Sym};
 
 /// Problems in the process of execution
@@ -11,7 +10,7 @@ pub enum RuntimeError {
   /// A Rust function encountered an error
   Extern(Rc<dyn ExternError>),
   /// Primitive applied as function
-  NonFunctionApplication(ExprInst),
+  NonFunctionApplication(Location),
   /// Symbol not in context
   MissingSymbol(Sym, Location),
 }
@@ -24,8 +23,8 @@ impl Display for RuntimeError {
   fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
     match self {
       Self::Extern(e) => write!(f, "Error in external function: {e}"),
-      Self::NonFunctionApplication(expr) => {
-        write!(f, "Primitive applied as function at {}", expr.expr().location)
+      Self::NonFunctionApplication(location) => {
+        write!(f, "Primitive applied as function at {}", location)
       },
       Self::MissingSymbol(sym, loc) => {
         write!(
diff --git a/src/interpreter/handler.rs b/src/interpreter/handler.rs
index 20a0f7a..3ee238f 100644
--- a/src/interpreter/handler.rs
+++ b/src/interpreter/handler.rs
@@ -5,12 +5,13 @@ use hashbrown::HashMap;
 use trait_set::trait_set;
 
 use super::{run, Context, Return, RuntimeError};
-use crate::foreign::ExternError;
-use crate::interpreted::{Clause, ExprInst};
+use crate::foreign::{Atom, Atomic, ExternError};
+use crate::interpreted::{Clause, Expr, ExprInst};
+use crate::utils::take_with_output;
 use crate::Primitive;
 
 trait_set! {
-  trait Handler = for<'b> FnMut(&'b dyn Any) -> HandlerRes;
+  trait Handler = FnMut(Box<dyn Any>) -> HandlerRes;
 }
 
 /// A table of command handlers
@@ -26,16 +27,22 @@ impl<'a> HandlerTable<'a> {
   /// next. This function can be impure.
   pub fn register<T: 'static>(
     &mut self,
-    mut f: impl for<'b> FnMut(&'b T) -> HandlerRes + 'a,
+    mut f: impl FnMut(Box<T>) -> HandlerRes + 'a,
   ) {
-    let cb = move |a: &dyn Any| f(a.downcast_ref().expect("found by TypeId"));
+    let cb = move |a: Box<dyn Any>| f(a.downcast().expect("found by TypeId"));
     let prev = self.handlers.insert(TypeId::of::<T>(), Box::new(cb));
     assert!(prev.is_none(), "A handler for this type is already registered");
   }
 
   /// Find and execute the corresponding handler for this type
-  pub fn dispatch(&mut self, arg: &dyn Any) -> Option<HandlerRes> {
-    self.handlers.get_mut(&arg.type_id()).map(|f| f(arg))
+  pub fn dispatch(
+    &mut self,
+    arg: Box<dyn Atomic>,
+  ) -> Result<HandlerRes, Box<dyn Atomic>> {
+    match self.handlers.get_mut(&arg.as_any_ref().type_id()) {
+      Some(f) => Ok(f(arg.as_any())),
+      None => Err(arg),
+    }
   }
 
   /// Combine two non-overlapping handler sets
@@ -60,16 +67,23 @@ pub fn run_handler(
   mut ctx: Context,
 ) -> Result<Return, RuntimeError> {
   loop {
-    let ret = run(expr.clone(), ctx.clone())?;
-    if let Clause::P(Primitive::Atom(a)) = &ret.state.expr().clause {
-      if let Some(e) = handlers.dispatch(a.0.as_any()) {
-        expr = e?;
-        ctx.gas = ret.gas;
-        if ret.gas.map_or(true, |g| g > 0) {
-          continue;
+    let mut ret = run(expr, ctx.clone())?;
+    let quit = take_with_output(&mut ret.state, |exi| match exi.expr_val() {
+      Expr { clause: Clause::P(Primitive::Atom(a)), .. } => {
+        match handlers.dispatch(a.0) {
+          Err(b) => (Clause::P(Primitive::Atom(Atom(b))).wrap(), Ok(true)),
+          Ok(e) => match e {
+            Ok(expr) => (expr, Ok(false)),
+            Err(e) => (Clause::Bottom.wrap(), Err(e)),
+          },
         }
-      }
+      },
+      expr => (ExprInst::new(expr), Ok(true)),
+    })?;
+    if quit | ret.gas.map_or(false, |g| g == 0) {
+      return Ok(ret);
     }
-    return Ok(ret);
+    ctx.gas = ret.gas;
+    expr = ret.state;
   }
 }
diff --git a/src/interpreter/run.rs b/src/interpreter/run.rs
index 5664d68..02d66ed 100644
--- a/src/interpreter/run.rs
+++ b/src/interpreter/run.rs
@@ -7,41 +7,40 @@ use crate::representations::Primitive;
 
 /// Normalize an expression using beta reduction with memoization
 pub fn run(expr: ExprInst, mut ctx: Context) -> Result<Return, RuntimeError> {
-  let (state, (gas, inert)) =
-    expr.try_normalize(|cls, loc| -> Result<(Clause, _), RuntimeError> {
-      let mut i = cls.clone();
+  let (state, (gas, inert)) = expr.try_normalize(
+    |mut cls, loc| -> Result<(Clause, _), RuntimeError> {
       while ctx.gas.map(|g| g > 0).unwrap_or(true) {
-        match &i {
+        match cls {
           Clause::Apply { f, x } => {
-            let res = apply(f.clone(), x.clone(), ctx.clone())?;
+            let res = apply(f, x, ctx.clone())?;
             if res.inert {
-              return Ok((i, (res.gas, true)));
+              return Ok((res.state.expr_val().clause, (res.gas, true)));
             }
             ctx.gas = res.gas;
-            i = res.state.expr().clause.clone();
+            cls = res.state.expr().clause.clone();
           },
           Clause::P(Primitive::Atom(data)) => {
-            let ret = data.run(ctx.clone())?;
-            let AtomicReturn { clause, gas, inert } = ret;
+            let AtomicReturn { clause, gas, inert } = data.run(ctx.clone())?;
             if inert {
-              return Ok((i, (gas, true)));
+              return Ok((clause, (gas, true)));
             }
             ctx.gas = gas;
-            i = clause.clone();
+            cls = clause;
           },
           Clause::Constant(c) => {
-            let symval = (ctx.symbols.get(c)).ok_or_else(|| {
+            let symval = (ctx.symbols.get(&c)).ok_or_else(|| {
               RuntimeError::MissingSymbol(c.clone(), loc.clone())
             })?;
             ctx.gas = ctx.gas.map(|g| g - 1); // cost of lookup
-            i = symval.expr().clause.clone();
+            cls = symval.expr().clause.clone();
           },
           // non-reducible
-          _ => return Ok((i, (ctx.gas, true))),
+          _ => return Ok((cls, (ctx.gas, true))),
         }
       }
       // out of gas
-      Ok((i, (ctx.gas, false)))
-    })?;
+      Ok((cls, (ctx.gas, false)))
+    },
+  )?;
   Ok(Return { state, gas, inert })
 }
diff --git a/src/lib.rs b/src/lib.rs
index 7cb29ca..e0688ad 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -34,4 +34,4 @@ pub use representations::{
   Location, NameLike, OrcString, PathSet, Primitive, Sym, VName,
 };
 pub use utils::substack::Substack;
-pub use utils::{IdMap, Side};
+pub use utils::{ddispatch, take_with_output, thread_pool, IdMap, Side};
diff --git a/src/representations/interpreted.rs b/src/representations/interpreted.rs
index e7603f1..283fc58 100644
--- a/src/representations/interpreted.rs
+++ b/src/representations/interpreted.rs
@@ -13,10 +13,15 @@ use super::location::Location;
 use super::path_set::PathSet;
 use super::primitive::Primitive;
 use super::Literal;
+#[allow(unused)] // for doc
+use crate::foreign::Atomic;
 use crate::foreign::ExternError;
+use crate::utils::ddispatch::request;
+use crate::utils::take_with_output;
 use crate::Sym;
 
 /// An expression with metadata
+#[derive(Clone)]
 pub struct Expr {
   /// The actual value
   pub clause: Clause,
@@ -49,7 +54,7 @@ pub struct NotALiteral;
 /// Types automatically convertible from an [ExprInst]
 pub trait TryFromExprInst: Sized {
   /// Match and clone the value out of an [ExprInst]
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>>;
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>>;
 }
 
 /// A wrapper around expressions to handle their multiple occurences in
@@ -57,6 +62,18 @@ pub trait TryFromExprInst: Sized {
 #[derive(Clone)]
 pub struct ExprInst(pub Rc<RefCell<Expr>>);
 impl ExprInst {
+  /// Wrap an [Expr] in a shared container so that normalizatoin steps are
+  /// applied to all references
+  pub fn new(expr: Expr) -> Self { Self(Rc::new(RefCell::new(expr))) }
+
+  /// Take the [Expr] out of this container if it's the last reference to it, or
+  /// clone it out.
+  pub fn expr_val(self) -> Expr {
+    Rc::try_unwrap(self.0)
+      .map(|c| c.into_inner())
+      .unwrap_or_else(|rc| rc.as_ref().borrow().deref().clone())
+  }
+
   /// Read-only access to the shared expression instance
   ///
   /// # Panics
@@ -80,12 +97,15 @@ impl ExprInst {
   /// across the tree.
   pub fn try_normalize<T, E>(
     &self,
-    mapper: impl FnOnce(&Clause, &Location) -> Result<(Clause, T), E>,
+    mapper: impl FnOnce(Clause, &Location) -> Result<(Clause, T), E>,
   ) -> Result<(Self, T), E> {
-    let expr = self.expr();
-    let (new_clause, extra) = mapper(&expr.clause, &expr.location)?;
-    drop(expr);
-    self.expr_mut().clause = new_clause;
+    let extra = take_with_output(&mut *self.expr_mut(), |expr| {
+      let Expr { clause, location } = expr;
+      match mapper(clause, &location) {
+        Ok((clause, t)) => (Expr { clause, location }, Ok(t)),
+        Err(e) => (Expr { clause: Clause::Bottom, location }, Err(e)),
+      }
+    })?;
     Ok((self.clone(), extra))
   }
 
@@ -93,13 +113,12 @@ impl ExprInst {
   /// distinct expression. The new expression shares location info with
   /// the original but is normalized independently.
   pub fn try_update<T, E>(
-    &self,
-    mapper: impl FnOnce(&Clause, &Location) -> Result<(Clause, T), E>,
+    self,
+    mapper: impl FnOnce(Clause, Location) -> Result<(Clause, T), E>,
   ) -> Result<(Self, T), E> {
-    let expr = self.expr();
-    let (clause, extra) = mapper(&expr.clause, &expr.location)?;
-    let new_expr = Expr { clause, location: expr.location.clone() };
-    Ok((Self(Rc::new(RefCell::new(new_expr))), extra))
+    let Expr { clause, location } = self.expr_val();
+    let (clause, extra) = mapper(clause, location.clone())?;
+    Ok((Self::new(Expr { clause, location }), extra))
   }
 
   /// Call a predicate on the expression, returning whatever the
@@ -111,16 +130,22 @@ impl ExprInst {
 
   /// Call the predicate on the value inside this expression if it is a
   /// primitive
-  pub fn with_literal<T>(
-    &self,
-    predicate: impl FnOnce(&Literal) -> T,
-  ) -> Result<T, NotALiteral> {
-    let expr = self.expr();
-    if let Clause::P(Primitive::Literal(l)) = &expr.clause {
-      Ok(predicate(l))
-    } else {
-      Err(NotALiteral)
-    }
+  pub fn get_literal(self) -> Result<(Literal, Location), Self> {
+    Rc::try_unwrap(self.0).map_or_else(
+      |rc| {
+        if let Expr { clause: Clause::P(Primitive::Literal(li)), location } =
+          rc.as_ref().borrow().deref()
+        {
+          return Ok((li.clone(), location.clone()));
+        }
+        Err(Self(rc))
+      },
+      |cell| match cell.into_inner() {
+        Expr { clause: Clause::P(Primitive::Literal(li)), location } =>
+          Ok((li, location)),
+        expr => Err(Self::new(expr)),
+      },
+    )
   }
 
   /// Visit all expressions in the tree. The search can be exited early by
@@ -138,16 +163,31 @@ impl ExprInst {
       Clause::Apply { f, x } =>
         f.search_all(predicate).or_else(|| x.search_all(predicate)),
       Clause::Lambda { body, .. } => body.search_all(predicate),
-      Clause::Constant(_) | Clause::LambdaArg | Clause::P(_) => None,
+      Clause::Constant(_)
+      | Clause::LambdaArg
+      | Clause::P(_)
+      | Clause::Bottom => None,
     })
   }
 
   /// Convert into any type that implements [FromExprInst]. Calls to this
   /// function are generated wherever a conversion is elided in an extern
   /// function.
-  pub fn downcast<T: TryFromExprInst>(&self) -> Result<T, Rc<dyn ExternError>> {
+  pub fn downcast<T: TryFromExprInst>(self) -> Result<T, Rc<dyn ExternError>> {
     T::from_exi(self)
   }
+
+  /// Get the code location data associated with this expresssion directly
+  pub fn location(&self) -> Location { self.expr().location.clone() }
+
+  /// If this expression is an [Atomic], request an object of the given type.
+  /// If it's not an atomic, fail the request automatically.
+  pub fn request<T: 'static>(&self) -> Option<T> {
+    match &self.expr().clause {
+      Clause::P(Primitive::Atom(a)) => request(&*a.0),
+      _ => None,
+    }
+  }
 }
 
 impl Debug for ExprInst {
@@ -171,6 +211,8 @@ impl Display for ExprInst {
 /// Distinct types of expressions recognized by the interpreter
 #[derive(Debug, Clone)]
 pub enum Clause {
+  /// An expression that causes an error
+  Bottom,
   /// An unintrospectable unit
   P(Primitive),
   /// A function application
@@ -210,6 +252,7 @@ impl Display for Clause {
   fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
     match self {
       Clause::P(p) => write!(f, "{p:?}"),
+      Clause::Bottom => write!(f, "bottom"),
       Clause::LambdaArg => write!(f, "arg"),
       Clause::Apply { f: fun, x } => write!(f, "({fun} {x})"),
       Clause::Lambda { args, body } => match args {
diff --git a/src/representations/string.rs b/src/representations/string.rs
index 7b910fc..d723c91 100644
--- a/src/representations/string.rs
+++ b/src/representations/string.rs
@@ -25,7 +25,13 @@ impl Debug for OrcString {
 
 impl OrcString {
   /// Clone out the plain Rust [String]
-  pub fn get_string(&self) -> String { self.as_str().to_owned() }
+  pub fn get_string(self) -> String {
+    match self {
+      Self::Interned(s) => s.as_str().to_owned(),
+      Self::Runtime(rc) =>
+        Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone()),
+    }
+  }
 }
 
 impl Deref for OrcString {
diff --git a/src/systems/assertion_error.rs b/src/systems/assertion_error.rs
index 6046a22..5086966 100644
--- a/src/systems/assertion_error.rs
+++ b/src/systems/assertion_error.rs
@@ -2,35 +2,39 @@ use std::fmt::Display;
 use std::rc::Rc;
 
 use crate::foreign::ExternError;
-use crate::representations::interpreted::ExprInst;
+use crate::Location;
 
 /// Some expectation (usually about the argument types of a function) did not
 /// hold.
 #[derive(Clone)]
 pub struct AssertionError {
-  value: ExprInst,
-  assertion: &'static str,
+  location: Location,
+  message: &'static str,
 }
 
 impl AssertionError {
   /// Construct, upcast and wrap in a Result that never succeeds for easy
   /// short-circuiting
   pub fn fail<T>(
-    value: ExprInst,
-    assertion: &'static str,
+    location: Location,
+    message: &'static str,
   ) -> Result<T, Rc<dyn ExternError>> {
-    return Err(Self { value, assertion }.into_extern());
+    return Err(Self { location, message }.into_extern());
   }
 
   /// Construct and upcast to [ExternError]
-  pub fn ext(value: ExprInst, assertion: &'static str) -> Rc<dyn ExternError> {
-    return Self { value, assertion }.into_extern();
+  pub fn ext(location: Location, message: &'static str) -> Rc<dyn ExternError> {
+    return Self { location, message }.into_extern();
   }
 }
 
 impl Display for AssertionError {
   fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-    write!(f, "Error: {:?} is not {}", self.value, self.assertion)
+    write!(f, "Error: expected {}", self.message)?;
+    if self.location != Location::Unknown {
+      write!(f, " at {}", self.location)?;
+    }
+    Ok(())
   }
 }
 
diff --git a/src/systems/asynch/system.rs b/src/systems/asynch/system.rs
index 0837a72..06fe66f 100644
--- a/src/systems/asynch/system.rs
+++ b/src/systems/asynch/system.rs
@@ -29,10 +29,7 @@ define_fn! {expr=x in
   SetTimer {
     recurring: Boolean,
     duration: NotNan<f64>
-  } => Ok(init_cps(2, Timer{
-    recurring: *recurring,
-    duration: *duration
-  }))
+  } => Ok(init_cps(2, Timer{ recurring, duration }))
 }
 
 #[derive(Clone)]
@@ -125,27 +122,27 @@ impl<'a> IntoSystem<'a> for AsynchSystem<'a> {
     let polly = Rc::new(RefCell::new(poller));
     handler_table.register({
       let polly = polly.clone();
-      move |t: &CPSBox<Timer>| {
+      move |t: Box<CPSBox<Timer>>| {
         let mut polly = polly.borrow_mut();
         let (timeout, action, cont) = t.unpack2();
         let duration = Duration::from_secs_f64(*timeout.duration);
         let cancel_timer = if timeout.recurring.0 {
-          CancelTimer(Rc::new(polly.set_interval(duration, action.clone())))
+          CancelTimer(Rc::new(polly.set_interval(duration, action)))
         } else {
-          CancelTimer(Rc::new(polly.set_timeout(duration, action.clone())))
+          CancelTimer(Rc::new(polly.set_timeout(duration, action)))
         };
-        Ok(call(cont.clone(), [init_cps(1, cancel_timer).wrap()]).wrap())
+        Ok(call(cont, [init_cps(1, cancel_timer).wrap()]).wrap())
       }
     });
-    handler_table.register(move |t: &CPSBox<CancelTimer>| {
+    handler_table.register(move |t: Box<CPSBox<CancelTimer>>| {
       let (command, cont) = t.unpack1();
       command.0.as_ref()();
-      Ok(cont.clone())
+      Ok(cont)
     });
     handler_table.register({
       let polly = polly.clone();
       let mut microtasks = VecDeque::new();
-      move |_: &Yield| {
+      move |_: Box<Yield>| {
         if let Some(expr) = microtasks.pop_front() {
           return Ok(expr);
         }
diff --git a/src/systems/cast_exprinst.rs b/src/systems/cast_exprinst.rs
index 462a179..99adba7 100644
--- a/src/systems/cast_exprinst.rs
+++ b/src/systems/cast_exprinst.rs
@@ -5,88 +5,61 @@ use std::rc::Rc;
 use ordered_float::NotNan;
 
 use super::assertion_error::AssertionError;
-use crate::foreign::{Atom, Atomic, ExternError};
-use crate::interpreted::{Clause, TryFromExprInst};
+use crate::foreign::{Atom, ExternError};
+use crate::interpreted::{Clause, Expr, TryFromExprInst};
 use crate::representations::interpreted::ExprInst;
 use crate::representations::{Literal, OrcString};
-use crate::Primitive;
+use crate::{Location, Primitive};
 
-/// Tries to cast the [ExprInst] as a [Literal], calls the provided function on
-/// it if successful. Returns a generic [AssertionError] if not.
-pub fn with_lit<T>(
-  x: &ExprInst,
-  predicate: impl FnOnce(&Literal) -> Result<T, Rc<dyn ExternError>>,
-) -> Result<T, Rc<dyn ExternError>> {
-  x.with_literal(predicate)
-    .map_err(|_| AssertionError::ext(x.clone(), "a literal value"))
-    .and_then(|r| r)
-}
-
-/// Like [with_lit] but also unwraps [Literal::Str]
-pub fn with_str<T>(
-  x: &ExprInst,
-  predicate: impl FnOnce(&OrcString) -> Result<T, Rc<dyn ExternError>>,
-) -> Result<T, Rc<dyn ExternError>> {
-  with_lit(x, |l| match l {
-    Literal::Str(s) => predicate(s),
-    _ => AssertionError::fail(x.clone(), "a string"),
-  })
-}
-
-/// If the [ExprInst] stores an [Atom], maps the predicate over it, otherwise
-/// raises a runtime error.
-pub fn with_atom<T>(
-  x: &ExprInst,
-  predicate: impl FnOnce(&Atom) -> Result<T, Rc<dyn ExternError>>,
-) -> Result<T, Rc<dyn ExternError>> {
-  x.inspect(|c| match c {
-    Clause::P(Primitive::Atom(a)) => predicate(a),
-    _ => AssertionError::fail(x.clone(), "an atom"),
-  })
-}
-
-/// Tries to cast the [ExprInst] into the specified atom type. Throws an
-/// assertion error if unsuccessful, or calls the provided function on the
-/// extracted atomic type.
-pub fn with_atomic<T: Atomic, U>(
-  x: &ExprInst,
-  inexact_typename: &'static str,
-  predicate: impl FnOnce(&T) -> Result<U, Rc<dyn ExternError>>,
-) -> Result<U, Rc<dyn ExternError>> {
-  with_atom(x, |a| match a.try_cast() {
-    Some(atomic) => predicate(atomic),
-    _ => AssertionError::fail(x.clone(), inexact_typename),
-  })
+/// [ExprInst::get_literal] except the error is mapped to an [ExternError]
+pub fn get_literal(
+  exi: ExprInst,
+) -> Result<(Literal, Location), Rc<dyn ExternError>> {
+  (exi.get_literal())
+    .map_err(|exi| AssertionError::ext(exi.location(), "literal"))
 }
 
 // ######## Automatically ########
 
 impl TryFromExprInst for Literal {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_lit(exi, |l| Ok(l.clone()))
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    get_literal(exi).map(|(l, _)| l)
   }
 }
 
 impl TryFromExprInst for OrcString {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_str(exi, |s| Ok(s.clone()))
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    match get_literal(exi)? {
+      (Literal::Str(s), _) => Ok(s),
+      (_, location) => AssertionError::fail(location, "string"),
+    }
   }
 }
 
 impl TryFromExprInst for u64 {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_lit(exi, |l| match l {
-      Literal::Uint(u) => Ok(*u),
-      _ => AssertionError::fail(exi.clone(), "an uint"),
-    })
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    match get_literal(exi)? {
+      (Literal::Uint(u), _) => Ok(u),
+      (_, location) => AssertionError::fail(location, "uint"),
+    }
   }
 }
 
 impl TryFromExprInst for NotNan<f64> {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_lit(exi, |l| match l {
-      Literal::Num(n) => Ok(*n),
-      _ => AssertionError::fail(exi.clone(), "a float"),
-    })
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    match get_literal(exi)? {
+      (Literal::Num(n), _) => Ok(n),
+      (_, location) => AssertionError::fail(location, "float"),
+    }
+  }
+}
+
+impl TryFromExprInst for Atom {
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    let Expr { clause, location } = exi.expr_val();
+    match clause {
+      Clause::P(Primitive::Atom(a)) => Ok(a),
+      _ => AssertionError::fail(location, "atom"),
+    }
   }
 }
diff --git a/src/systems/directfs/commands.rs b/src/systems/directfs/commands.rs
new file mode 100644
index 0000000..36aef94
--- /dev/null
+++ b/src/systems/directfs/commands.rs
@@ -0,0 +1,19 @@
+use crate::foreign::cps_box::init_cps;
+use crate::foreign::InertAtomic;
+use crate::systems::asynch::MessagePort;
+use crate::systems::scheduler::SeqScheduler;
+use crate::{define_fn, OrcString};
+
+#[derive(Debug, Clone)]
+struct ReadFile(OrcString);
+impl InertAtomic for ReadFile {
+  fn type_str() -> &'static str { "a readfile command" }
+}
+
+pub fn read_file(port: MessagePort, cmd: ReadFile) -> Vec<ExprInst> {
+  let new_file = 
+}
+
+define_fn! {
+  pub OpenFileRead = |x| Ok(init_cps(3, ReadFile(x.downcast()?)))
+}
diff --git a/src/systems/directfs/mod.rs b/src/systems/directfs/mod.rs
new file mode 100644
index 0000000..6de2606
--- /dev/null
+++ b/src/systems/directfs/mod.rs
@@ -0,0 +1,2 @@
+
+mod commands;
diff --git a/src/systems/io/bindings.rs b/src/systems/io/bindings.rs
index b09ec46..80977e7 100644
--- a/src/systems/io/bindings.rs
+++ b/src/systems/io/bindings.rs
@@ -13,63 +13,49 @@ define_fn! {
   ReadString = |x| Ok(init_cps(3, IOCmdHandlePack{
     cmd: ReadCmd::RStr(SRead::All),
     handle: x.downcast()?
-  }))
-}
-define_fn! {
+  }));
   ReadLine = |x| Ok(init_cps(3, IOCmdHandlePack{
     cmd: ReadCmd::RStr(SRead::Line),
     handle: x.downcast()?
-  }))
-}
-define_fn! {
+  }));
   ReadBin = |x| Ok(init_cps(3, IOCmdHandlePack{
     cmd: ReadCmd::RBytes(BRead::All),
     handle: x.downcast()?
-  }))
-}
-define_fn! {
+  }));
   ReadBytes {
     stream: SourceHandle,
     n: u64
   } => Ok(init_cps(3, IOCmdHandlePack{
-    cmd: ReadCmd::RBytes(BRead::N((*n).try_into().unwrap())),
+    cmd: ReadCmd::RBytes(BRead::N(n.try_into().unwrap())),
     handle: stream.clone()
-  }))
-}
-define_fn! {
+  }));
   ReadUntil {
     stream: SourceHandle,
     pattern: u64
   } => {
-    let delim = (*pattern).try_into().map_err(|_| RuntimeError::ext(
+    let delim = pattern.try_into().map_err(|_| RuntimeError::ext(
       "greater than 255".to_string(),
       "converting number to byte"
     ))?;
     Ok(init_cps(3, IOCmdHandlePack{
       cmd: ReadCmd::RBytes(BRead::Until(delim)),
-      handle: stream.clone()
+      handle: stream
     }))
-  }
-}
-define_fn! {
+  };
   WriteStr {
     stream: SinkHandle,
     string: OrcString
   } => Ok(init_cps(3, IOCmdHandlePack {
     cmd: WriteCmd::WStr(string.get_string()),
     handle: stream.clone(),
-  }))
-}
-define_fn! {
+  }));
   WriteBin {
     stream: SinkHandle,
     bytes: Binary
   } => Ok(init_cps(3, IOCmdHandlePack {
-    cmd: WriteCmd::WBytes(bytes.clone()),
+    cmd: WriteCmd::WBytes(bytes),
     handle: stream.clone(),
-  }))
-}
-define_fn! {
+  }));
   Flush = |x| Ok(init_cps(3, IOCmdHandlePack {
     cmd: WriteCmd::Flush,
     handle: x.downcast()?
diff --git a/src/systems/io/service.rs b/src/systems/io/service.rs
index 611cf08..b2d397e 100644
--- a/src/systems/io/service.rs
+++ b/src/systems/io/service.rs
@@ -56,30 +56,29 @@ impl<'a, ST: IntoIterator<Item = (&'a str, Stream)>> IntoSystem<'static>
   fn into_system(self, i: &crate::Interner) -> crate::facade::System<'static> {
     let scheduler = self.scheduler.clone();
     let mut handlers = HandlerTable::new();
-    handlers.register(move |cps: &CPSBox<IOCmdHandlePack<ReadCmd>>| {
+    handlers.register(move |cps: Box<CPSBox<IOCmdHandlePack<ReadCmd>>>| {
       let (IOCmdHandlePack { cmd, handle }, succ, fail, tail) = cps.unpack3();
-      let (cmd, succ1, fail1) = (*cmd, succ.clone(), fail.clone());
+      let fail1 = fail.clone();
       let result = scheduler.schedule(
-        handle.clone(),
+        handle,
         move |mut stream, cancel| {
           let ret = cmd.execute(&mut stream, cancel);
           (stream, ret)
         },
-        move |stream, res, _cancel| (stream, res.dispatch(succ1, fail1)),
+        move |stream, res, _cancel| (stream, res.dispatch(succ, fail1)),
         |stream| (stream, Vec::new()),
       );
       match result {
-        Ok(cancel) =>
-          Ok(call(tail.clone(), vec![init_cps(1, cancel).wrap()]).wrap()),
-        Err(e) => Ok(call(fail.clone(), vec![e.atom_exi()]).wrap()),
+        Ok(cancel) => Ok(call(tail, vec![init_cps(1, cancel).wrap()]).wrap()),
+        Err(e) => Ok(call(fail, vec![e.atom_exi()]).wrap()),
       }
     });
     let scheduler = self.scheduler.clone();
-    handlers.register(move |cps: &CPSBox<IOCmdHandlePack<WriteCmd>>| {
+    handlers.register(move |cps: Box<CPSBox<IOCmdHandlePack<WriteCmd>>>| {
       let (IOCmdHandlePack { cmd, handle }, succ, fail, tail) = cps.unpack3();
-      let (cmd, succ1, fail1) = (cmd.clone(), succ.clone(), fail.clone());
+      let (succ1, fail1) = (succ, fail.clone());
       let result = scheduler.schedule(
-        handle.clone(),
+        handle,
         move |mut stream, cancel| {
           let ret = cmd.execute(&mut stream, cancel);
           (stream, ret)
@@ -88,9 +87,8 @@ impl<'a, ST: IntoIterator<Item = (&'a str, Stream)>> IntoSystem<'static>
         |stream| (stream, Vec::new()),
       );
       match result {
-        Ok(cancel) =>
-          Ok(call(tail.clone(), vec![init_cps(1, cancel).wrap()]).wrap()),
-        Err(e) => Ok(call(fail.clone(), vec![e.atom_exi()]).wrap()),
+        Ok(cancel) => Ok(call(tail, vec![init_cps(1, cancel).wrap()]).wrap()),
+        Err(e) => Ok(call(fail, vec![e.atom_exi()]).wrap()),
       }
     });
     let streams = self.global_streams.into_iter().map(|(n, stream)| {
diff --git a/src/systems/mod.rs b/src/systems/mod.rs
index fa0f603..9380219 100644
--- a/src/systems/mod.rs
+++ b/src/systems/mod.rs
@@ -3,7 +3,7 @@ mod assertion_error;
 pub mod asynch;
 pub mod cast_exprinst;
 pub mod codegen;
-mod directfs;
+// mod directfs;
 pub mod io;
 mod runtime_error;
 pub mod scheduler;
diff --git a/src/systems/scheduler/system.rs b/src/systems/scheduler/system.rs
index c13bd85..7eec7b9 100644
--- a/src/systems/scheduler/system.rs
+++ b/src/systems/scheduler/system.rs
@@ -15,10 +15,9 @@ use crate::foreign::InertAtomic;
 use crate::interpreted::ExprInst;
 use crate::interpreter::HandlerTable;
 use crate::systems::asynch::{AsynchSystem, MessagePort};
-use crate::systems::cast_exprinst::with_atom;
 use crate::systems::stl::Boolean;
 use crate::systems::AssertionError;
-use crate::utils::ddispatch::{request, Request};
+use crate::utils::ddispatch::Request;
 use crate::utils::thread_pool::ThreadPool;
 use crate::utils::{take_with_output, unwrap_or, IdMap};
 use crate::{define_fn, ConstTree};
@@ -117,12 +116,6 @@ impl Debug for TakeCmd {
     write!(f, "A command to drop a shared resource")
   }
 }
-define_fn! {
-  pub TakeAndDrop = |x| with_atom(x, |a| match request(a.0.as_ref()) {
-    Some(t) => Ok(init_cps::<TakeCmd>(1, t)),
-    None => AssertionError::fail(x.clone(), "a SharedHandle"),
-  })
-}
 
 /// Error produced when an operation is scheduled or a seal placed on a resource
 /// which is either already sealed or taken.
@@ -135,6 +128,13 @@ impl InertAtomic for SealedOrTaken {
 }
 
 define_fn! {
+  pub TakeAndDrop = |x| {
+    let location = x.location();
+    match x.request() {
+      Some(t) => Ok(init_cps::<TakeCmd>(1, t)),
+      None => AssertionError::fail(location, "SharedHandle"),
+    }
+  };
   IsTakenError = |x| {
     Ok(Boolean(x.downcast::<SealedOrTaken>().is_ok()).atom_cls())
   }
@@ -296,15 +296,15 @@ impl SeqScheduler {
 impl IntoSystem<'static> for SeqScheduler {
   fn into_system(self, i: &crate::Interner) -> crate::facade::System<'static> {
     let mut handlers = HandlerTable::new();
-    handlers.register(|cmd: &CPSBox<Canceller>| {
+    handlers.register(|cmd: Box<CPSBox<Canceller>>| {
       let (canceller, cont) = cmd.unpack1();
       canceller.cancel();
-      Ok(cont.clone())
+      Ok(cont)
     });
-    handlers.register(move |cmd: &CPSBox<TakeCmd>| {
+    handlers.register(move |cmd: Box<CPSBox<TakeCmd>>| {
       let (TakeCmd(cb), cont) = cmd.unpack1();
       cb(self.clone());
-      Ok(cont.clone())
+      Ok(cont)
     });
     System {
       name: ["system", "scheduler"].into_iter().map_into().collect(),
diff --git a/src/systems/stl/bin.rs b/src/systems/stl/bin.rs
index fca4950..78ee66b 100644
--- a/src/systems/stl/bin.rs
+++ b/src/systems/stl/bin.rs
@@ -33,29 +33,34 @@ impl Debug for Binary {
   }
 }
 
-define_fn! {expr=x in
+define_fn! {
+  /// Detect the number of bytes in the binary data block
+  pub Size = |x| {
+    Ok(Literal::Uint(x.downcast::<Binary>()?.0.len() as u64).into())
+  };
+
+expr=x in
+
   /// Convert a number into a binary blob
   pub FromNum {
     size: u64,
     is_little_endian: Boolean,
     data: u64
   } => {
-    if size > &8 {
+    if size > 8 {
       RuntimeError::fail(
         "more than 8 bytes requested".to_string(),
         "converting number to binary"
       )?
     }
     let bytes = if is_little_endian.0 {
-      data.to_le_bytes()[0..*size as usize].to_vec()
+      data.to_le_bytes()[0..size as usize].to_vec()
     } else {
-      data.to_be_bytes()[8 - *size as usize..].to_vec()
+      data.to_be_bytes()[8 - size as usize..].to_vec()
     };
     Ok(Binary(Arc::new(bytes)).atom_cls())
-  }
-}
+  };
 
-define_fn! {expr=x in
   /// Read a number from a binary blob
   pub GetNum {
     buf: Binary,
@@ -69,34 +74,30 @@ define_fn! {expr=x in
         "reading number from binary data"
       )?
     }
-    if 8 < *size {
+    if 8 < size {
       RuntimeError::fail(
         "more than 8 bytes provided".to_string(),
         "reading number from binary data"
       )?
     }
     let mut data = [0u8; 8];
-    let section = &buf.0[*loc as usize..(loc + size) as usize];
+    let section = &buf.0[loc as usize..(loc + size) as usize];
     let num = if is_little_endian.0 {
-      data[0..*size as usize].copy_from_slice(section);
+      data[0..size as usize].copy_from_slice(section);
       u64::from_le_bytes(data)
     } else {
-      data[8 - *size as usize..].copy_from_slice(section);
+      data[8 - size as usize..].copy_from_slice(section);
       u64::from_be_bytes(data)
     };
     Ok(Literal::Uint(num).into())
-  }
-}
+  };
 
-define_fn! {expr=x in
   /// Append two binary data blocks
   pub Concatenate { a: Binary, b: Binary } => {
     let data = a.0.iter().chain(b.0.iter()).copied().collect();
     Ok(Binary(Arc::new(data)).atom_cls())
-  }
-}
+  };
 
-define_fn! {expr=x in
   /// Extract a subsection of the binary data
   pub Slice { s: Binary, i: u64, len: u64 } => {
     if i + len < s.0.len() as u64 {
@@ -105,30 +106,25 @@ define_fn! {expr=x in
         "indexing binary"
       )?
     }
-    let data = s.0[*i as usize..*i as usize + *len as usize].to_vec();
+    let data = s.0[i as usize..i as usize + len as usize].to_vec();
     Ok(Binary(Arc::new(data)).atom_cls())
-  }
-}
+  };
 
-define_fn! {expr=x in
   /// Return the index where the first argument first contains the second,
   /// if any
   pub Find { haystack: Binary, needle: Binary } => {
     let found = iter_find(haystack.0.iter(), needle.0.iter());
     Ok(orchid_opt(found.map(|x| Literal::Uint(x as u64).into())))
-  }
-}
-
-define_fn! {expr=x in
+  };
   /// Split binary data block into two smaller blocks
   pub Split { bin: Binary, i: u64 } => {
-    if bin.0.len() < *i as usize {
+    if bin.0.len() < i as usize {
       RuntimeError::fail(
         "Byte index out of bounds".to_string(),
         "splitting binary"
       )?
     }
-    let (asl, bsl) = bin.0.split_at(*i as usize);
+    let (asl, bsl) = bin.0.split_at(i as usize);
     Ok(tuple(vec![
       Binary(Arc::new(asl.to_vec())).atom_cls().into(),
       Binary(Arc::new(bsl.to_vec())).atom_cls().into(),
@@ -136,13 +132,6 @@ define_fn! {expr=x in
   }
 }
 
-define_fn! {
-  /// Detect the number of bytes in the binary data block
-  pub Size = |x| {
-    Ok(Literal::Uint(x.downcast::<Binary>()?.0.len() as u64).into())
-  }
-}
-
 pub fn bin(i: &Interner) -> ConstTree {
   ConstTree::tree([(
     i.i("bin"),
diff --git a/src/systems/stl/bool.rs b/src/systems/stl/bool.rs
index 3bdf185..98e6e3d 100644
--- a/src/systems/stl/bool.rs
+++ b/src/systems/stl/bool.rs
@@ -4,7 +4,7 @@ use crate::foreign::InertAtomic;
 use crate::interner::Interner;
 use crate::representations::interpreted::Clause;
 use crate::systems::AssertionError;
-use crate::{define_fn, ConstTree, Literal, PathSet};
+use crate::{define_fn, ConstTree, Literal, Location, PathSet};
 
 /// Booleans exposed to Orchid
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -17,7 +17,26 @@ impl From<bool> for Boolean {
   fn from(value: bool) -> Self { Self(value) }
 }
 
-define_fn! {expr=x in
+define_fn! {
+  /// Takes a boolean and two branches, runs the first if the bool is true, the
+  /// second if it's false.
+  // Even though it's a ternary function, IfThenElse is implemented as an unary
+  // foreign function, as the rest of the logic can be defined in Orchid.
+  IfThenElse = |x| x.downcast().map(|Boolean(b)| if b {Clause::Lambda {
+    args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
+    body: Clause::Lambda {
+      args: None,
+      body: Clause::LambdaArg.wrap()
+    }.wrap(),
+  }} else {Clause::Lambda {
+    args: None,
+    body: Clause::Lambda {
+      args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
+      body: Clause::LambdaArg.wrap(),
+    }.wrap(),
+  }});
+
+expr=x in
   /// Compares the inner values if
   ///
   /// - both are string,
@@ -26,34 +45,12 @@ define_fn! {expr=x in
     (Literal::Str(s1), Literal::Str(s2)) => s1 == s2,
     (Literal::Num(n1), Literal::Num(n2)) => n1 == n2,
     (Literal::Uint(i1), Literal::Uint(i2)) => i1 == i2,
-    (Literal::Num(n1), Literal::Uint(u1)) => *n1 == (*u1 as f64),
-    (Literal::Uint(u1), Literal::Num(n1)) => *n1 == (*u1 as f64),
-    (..) => AssertionError::fail(b.clone().into(), "the expected type")?,
+    (Literal::Num(n1), Literal::Uint(u1)) => *n1 == (u1 as f64),
+    (Literal::Uint(u1), Literal::Num(n1)) => *n1 == (u1 as f64),
+    (..) => AssertionError::fail(Location::Unknown, "the expected type")?,
   }).atom_cls())
 }
 
-// Even though it's a ternary function, IfThenElse is implemented as an unary
-// foreign function, as the rest of the logic can be defined in Orchid.
-define_fn! {
-  /// Takes a boolean and two branches, runs the first if the bool is true, the
-  /// second if it's false.
-  IfThenElse = |x| x.downcast()
-    .map_err(|_| AssertionError::ext(x.clone(), "a boolean"))
-    .map(|b: Boolean| if b.0 {Clause::Lambda {
-      args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
-      body: Clause::Lambda {
-        args: None,
-        body: Clause::LambdaArg.wrap()
-      }.wrap(),
-    }} else {Clause::Lambda {
-      args: None,
-      body: Clause::Lambda {
-        args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
-        body: Clause::LambdaArg.wrap(),
-      }.wrap(),
-    }})
-}
-
 pub fn bool(i: &Interner) -> ConstTree {
   ConstTree::tree([(
     i.i("bool"),
diff --git a/src/systems/stl/conv.rs b/src/systems/stl/conv.rs
index b1a83c9..cf33e57 100644
--- a/src/systems/stl/conv.rs
+++ b/src/systems/stl/conv.rs
@@ -6,48 +6,38 @@ use crate::foreign::ExternError;
 use crate::interner::Interner;
 use crate::interpreted::Clause;
 use crate::parse::{float_parser, int_parser};
-use crate::systems::cast_exprinst::with_lit;
+use crate::systems::cast_exprinst::get_literal;
 use crate::systems::AssertionError;
 use crate::{define_fn, ConstTree, Literal};
 
 define_fn! {
   /// parse a number. Accepts the same syntax Orchid does.
-  ToFloat = |x| with_lit(x, |l| match l {
-    Literal::Str(s) => float_parser()
+  ToFloat = |x| match get_literal(x)? {
+    (Literal::Str(s), loc) => float_parser()
       .parse(s.as_str())
-      .map_err(|_| AssertionError::ext(
-        x.clone(),
-        "cannot be parsed into a float"
-      )),
-    Literal::Num(n) => Ok(*n),
-    Literal::Uint(i) => NotNan::new(*i as f64)
+      .map_err(|_| AssertionError::ext(loc, "float syntax")),
+    (Literal::Num(n), _) => Ok(n),
+    (Literal::Uint(i), _) => NotNan::new(i as f64)
       .map_err(|_| ArithmeticError::NaN.into_extern()),
-  }).map(|nn| Literal::Num(nn).into())
-}
+  }.map(|nn| Literal::Num(nn).into());
 
-define_fn! {
   /// Parse an unsigned integer. Accepts the same formats Orchid does. If the
   /// input is a number, floors it.
-  ToUint = |x| with_lit(x, |l| match l {
-    Literal::Str(s) => int_parser()
+  ToUint = |x| match get_literal(x)? {
+    (Literal::Str(s), loc) => int_parser()
       .parse(s.as_str())
-      .map_err(|_| AssertionError::ext(
-        x.clone(),
-        "cannot be parsed into an unsigned int",
-      )),
-    Literal::Num(n) => Ok(n.floor() as u64),
-    Literal::Uint(i) => Ok(*i),
-  }).map(|u| Literal::Uint(u).into())
-}
+      .map_err(|_| AssertionError::ext(loc, "int syntax")),
+    (Literal::Num(n), _) => Ok(n.floor() as u64),
+    (Literal::Uint(i), _) => Ok(i),
+  }.map(|u| Literal::Uint(u).into());
 
-define_fn! {
   /// Convert a literal to a string using Rust's conversions for floats, chars and
   /// uints respectively
-  ToString = |x| with_lit(x, |l| Ok(match l {
-    Literal::Uint(i) => Literal::Str(i.to_string().into()),
-    Literal::Num(n) => Literal::Str(n.to_string().into()),
-    s@Literal::Str(_) => s.clone(),
-  })).map(Clause::from)
+  ToString = |x| Ok(match get_literal(x)?.0 {
+    Literal::Uint(i) => Clause::from(Literal::Str(i.to_string().into())),
+    Literal::Num(n) => Clause::from(Literal::Str(n.to_string().into())),
+    s@Literal::Str(_) => Clause::from(s),
+  })
 }
 
 pub fn conv(i: &Interner) -> ConstTree {
diff --git a/src/systems/stl/inspect.rs b/src/systems/stl/inspect.rs
index 75d1114..6fdf7ab 100644
--- a/src/systems/stl/inspect.rs
+++ b/src/systems/stl/inspect.rs
@@ -18,8 +18,9 @@ struct Inspect1 {
 }
 impl Responder for Inspect1 {}
 impl Atomic for Inspect1 {
-  fn as_any(&self) -> &dyn std::any::Any { self }
-  fn run(&self, ctx: Context) -> crate::foreign::AtomicResult {
+  fn as_any(self: Box<Self>) -> Box<dyn std::any::Any> { self }
+  fn as_any_ref(&self) -> &dyn std::any::Any { self }
+  fn run(self: Box<Self>, ctx: Context) -> crate::foreign::AtomicResult {
     println!("{}", self.expr_inst);
     Ok(AtomicReturn {
       clause: self.expr_inst.expr().clause.clone(),
diff --git a/src/systems/stl/num.rs b/src/systems/stl/num.rs
index 1900391..969d62e 100644
--- a/src/systems/stl/num.rs
+++ b/src/systems/stl/num.rs
@@ -7,7 +7,7 @@ use crate::foreign::ExternError;
 use crate::interpreted::TryFromExprInst;
 use crate::representations::interpreted::{Clause, ExprInst};
 use crate::representations::{Literal, Primitive};
-use crate::systems::cast_exprinst::with_lit;
+use crate::systems::cast_exprinst::get_literal;
 use crate::systems::AssertionError;
 use crate::{define_fn, ConstTree, Interner};
 
@@ -42,12 +42,12 @@ impl Numeric {
   }
 }
 impl TryFromExprInst for Numeric {
-  fn from_exi(exi: &ExprInst) -> Result<Self, Rc<dyn ExternError>> {
-    with_lit(exi, |l| match l {
-      Literal::Uint(i) => Ok(Numeric::Uint(*i)),
-      Literal::Num(n) => Ok(Numeric::Num(*n)),
-      _ => AssertionError::fail(exi.clone(), "an integer or number")?,
-    })
+  fn from_exi(exi: ExprInst) -> Result<Self, Rc<dyn ExternError>> {
+    match get_literal(exi)? {
+      (Literal::Uint(i), _) => Ok(Numeric::Uint(i)),
+      (Literal::Num(n), _) => Ok(Numeric::Num(n)),
+      (_, location) => AssertionError::fail(location, "an integer or number")?,
+    }
   }
 }
 
@@ -69,42 +69,36 @@ define_fn! {
   /// number, the output is number.
   Add { a: Numeric, b: Numeric } => match (a, b) {
     (Numeric::Uint(a), Numeric::Uint(b)) => {
-      a.checked_add(*b)
+      a.checked_add(b)
         .map(Numeric::Uint)
         .ok_or_else(|| ArithmeticError::Overflow.into_extern())
     }
     (Numeric::Num(a), Numeric::Num(b)) => Numeric::num(*(a + b)),
     (Numeric::Num(a), Numeric::Uint(b)) | (Numeric::Uint(b), Numeric::Num(a))
-    => Numeric::num(a.into_inner() + *b as f64),
-  }.map(Numeric::into)
-}
+    => Numeric::num(*a + b as f64),
+  }.map(Numeric::into);
 
-define_fn! {
   /// Subtract a number from another. Always returns Number.
   Subtract { a: Numeric, b: Numeric } => match (a, b) {
-    (Numeric::Uint(a), Numeric::Uint(b)) => Numeric::num(*a as f64 - *b as f64),
+    (Numeric::Uint(a), Numeric::Uint(b)) => Numeric::num(a as f64 - b as f64),
     (Numeric::Num(a), Numeric::Num(b)) => Numeric::num(*(a - b)),
-    (Numeric::Num(a), Numeric::Uint(b)) => Numeric::num(**a - *b as f64),
-    (Numeric::Uint(a), Numeric::Num(b)) => Numeric::num(*a as f64 - **b),
-  }.map(Numeric::into)
-}
+    (Numeric::Num(a), Numeric::Uint(b)) => Numeric::num(*a - b as f64),
+    (Numeric::Uint(a), Numeric::Num(b)) => Numeric::num(a as f64 - *b),
+  }.map(Numeric::into);
 
-define_fn! {
   /// Multiply two numbers. If they're both uint, the output is uint. If either
   /// is number, the output is number.
   Multiply { a: Numeric, b: Numeric } => match (a, b) {
     (Numeric::Uint(a), Numeric::Uint(b)) => {
-      a.checked_mul(*b)
+      a.checked_mul(b)
         .map(Numeric::Uint)
         .ok_or_else(|| ArithmeticError::Overflow.into_extern())
     }
     (Numeric::Num(a), Numeric::Num(b)) => Numeric::num(*(a * b)),
     (Numeric::Uint(a), Numeric::Num(b)) | (Numeric::Num(b), Numeric::Uint(a))
-      => Numeric::num(*a as f64 * **b),
-  }.map(Numeric::into)
-}
+      => Numeric::num(a as f64 * *b),
+  }.map(Numeric::into);
 
-define_fn! {
   /// Divide a number by another. Always returns Number.
   Divide { a: Numeric, b: Numeric } => {
     let a: f64 = a.as_f64();
@@ -113,21 +107,19 @@ define_fn! {
       return Err(ArithmeticError::DivByZero.into_extern())
     }
     Numeric::num(a / b).map(Numeric::into)
-  }
-}
+  };
 
-define_fn! {
   /// Take the remainder of two numbers.  If they're both uint, the output is
   /// uint. If either is number, the output is number.
   Remainder { a: Numeric, b: Numeric } => match (a, b) {
     (Numeric::Uint(a), Numeric::Uint(b)) => {
-      a.checked_rem(*b)
+      a.checked_rem(b)
         .map(Numeric::Uint)
         .ok_or_else(|| ArithmeticError::DivByZero.into_extern())
     }
     (Numeric::Num(a), Numeric::Num(b)) => Numeric::num(*(a % b)),
-    (Numeric::Uint(a), Numeric::Num(b)) => Numeric::num(*a as f64 % **b),
-    (Numeric::Num(a), Numeric::Uint(b)) => Numeric::num(**a % *b as f64),
+    (Numeric::Uint(a), Numeric::Num(b)) => Numeric::num(a as f64 % *b),
+    (Numeric::Num(a), Numeric::Uint(b)) => Numeric::num(*a % b as f64),
   }.map(Numeric::into)
 }
 
diff --git a/src/systems/stl/panic.rs b/src/systems/stl/panic.rs
index 55ee24b..afc9cf3 100644
--- a/src/systems/stl/panic.rs
+++ b/src/systems/stl/panic.rs
@@ -2,8 +2,7 @@ use std::fmt::Display;
 use std::rc::Rc;
 
 use crate::foreign::ExternError;
-use crate::systems::cast_exprinst::with_str;
-use crate::{define_fn, ConstTree, Interner};
+use crate::{define_fn, ConstTree, Interner, OrcString};
 
 /// An unrecoverable error in Orchid land. Because Orchid is lazy, this only
 /// invalidates expressions that reference the one that generated it.
@@ -19,10 +18,10 @@ impl ExternError for OrchidPanic {}
 
 define_fn! {
   /// Takes a message, returns an [ExternError] unconditionally.
-  Panic = |x| with_str(x, |s| {
-    let msg = Rc::new(s.get_string());
+  Panic = |x| {
+    let msg = Rc::new(x.downcast::<OrcString>()?.get_string());
     Err(OrchidPanic(msg).into_extern())
-  })
+  }
 }
 
 pub fn panic(i: &Interner) -> ConstTree {
diff --git a/src/systems/stl/state.rs b/src/systems/stl/state.rs
index bffe8ba..759392b 100644
--- a/src/systems/stl/state.rs
+++ b/src/systems/stl/state.rs
@@ -1,4 +1,5 @@
 use std::cell::RefCell;
+use std::ops::Deref;
 use std::rc::Rc;
 
 use crate::foreign::cps_box::{const_cps, init_cps, CPSBox};
@@ -23,31 +24,37 @@ struct SetStateCmd(State);
 #[derive(Debug, Clone)]
 struct GetStateCmd(State);
 
-define_fn! { SetState = |x| Ok(init_cps(2, SetStateCmd(x.downcast()?))) }
-define_fn! { GetState = |x| Ok(init_cps(2, GetStateCmd(x.downcast()?))) }
+define_fn! {
+  SetState = |x| Ok(init_cps(2, SetStateCmd(x.downcast()?)));
+  GetState = |x| Ok(init_cps(2, GetStateCmd(x.downcast()?)))
+}
 
-fn new_state_handler<E>(cmd: &CPSBox<NewStateCmd>) -> Result<ExprInst, E> {
+fn new_state_handler<E>(cmd: CPSBox<NewStateCmd>) -> Result<ExprInst, E> {
   let (_, default, handler) = cmd.unpack2();
-  let state = State(Rc::new(RefCell::new(default.clone())));
-  Ok(call(handler.clone(), [state.atom_exi()]).wrap())
+  let state = State(Rc::new(RefCell::new(default)));
+  Ok(call(handler, [state.atom_exi()]).wrap())
 }
 
-fn set_state_handler<E>(cmd: &CPSBox<SetStateCmd>) -> Result<ExprInst, E> {
+fn set_state_handler<E>(cmd: CPSBox<SetStateCmd>) -> Result<ExprInst, E> {
   let (SetStateCmd(state), value, handler) = cmd.unpack2();
-  *state.0.as_ref().borrow_mut() = value.clone();
-  Ok(handler.clone())
+  *state.0.as_ref().borrow_mut() = value;
+  Ok(handler)
 }
 
-fn get_state_handler<E>(cmd: &CPSBox<GetStateCmd>) -> Result<ExprInst, E> {
+fn get_state_handler<E>(cmd: CPSBox<GetStateCmd>) -> Result<ExprInst, E> {
   let (GetStateCmd(state), handler) = cmd.unpack1();
-  Ok(call(handler.clone(), [state.0.as_ref().borrow().clone()]).wrap())
+  let val = match Rc::try_unwrap(state.0) {
+    Ok(cell) => cell.into_inner(),
+    Err(rc) => rc.as_ref().borrow().deref().clone(),
+  };
+  Ok(call(handler, [val]).wrap())
 }
 
 pub fn state_handlers() -> HandlerTable<'static> {
   let mut handlers = HandlerTable::new();
-  handlers.register(new_state_handler);
-  handlers.register(get_state_handler);
-  handlers.register(set_state_handler);
+  handlers.register(|b| new_state_handler(*b));
+  handlers.register(|b| get_state_handler(*b));
+  handlers.register(|b| set_state_handler(*b));
   handlers
 }
 
diff --git a/src/systems/stl/str.rs b/src/systems/stl/str.rs
index 9ed956c..ec3828b 100644
--- a/src/systems/stl/str.rs
+++ b/src/systems/stl/str.rs
@@ -2,26 +2,37 @@ use unicode_segmentation::UnicodeSegmentation;
 
 use crate::interner::Interner;
 use crate::representations::OrcString;
-use crate::systems::cast_exprinst::with_str;
 use crate::systems::codegen::{orchid_opt, tuple};
 use crate::systems::RuntimeError;
 use crate::utils::iter_find;
 use crate::{define_fn, ConstTree, Literal};
 
-define_fn! {expr=x in
-  /// Append a string to another
-  pub Concatenate { a: OrcString, b: OrcString }
-  => Ok(Literal::Str((a.get_string() + b.as_str()).into()).into())
-}
+define_fn! {
+  pub Len = |x| Ok(Literal::Uint(
+    (*x.downcast::<OrcString>()?)
+      .graphemes(true)
+      .count() as u64
+  ).into());
+
+  pub Size = |x| Ok(Literal::Uint(
+    (*x.downcast::<OrcString>()?)
+      .as_bytes()
+      .len() as u64
+  ).into());
+
+expr=x in
+  /// Append a string to another
+  pub Concatenate { a: OrcString, b: OrcString } => Ok(
+    Literal::Str((a.get_string() + b.as_str()).into()).into()
+  );
 
-define_fn! {expr=x in
   pub Slice { s: OrcString, i: u64, len: u64 } => {
     let graphs = s.as_str().graphemes(true);
-    if *i == 0 {
-      let orc_str = graphs.take(*len as usize).collect::<String>().into();
+    if i == 0 {
+      let orc_str = graphs.take(len as usize).collect::<String>().into();
       Ok(Literal::Str(orc_str).into())
     } else {
-      let mut prefix = graphs.skip(*i as usize - 1);
+      let mut prefix = graphs.skip(i as usize - 1);
       if prefix.next().is_none() {
         RuntimeError::fail(
           "Character index out of bounds".to_string(),
@@ -29,10 +40,10 @@ define_fn! {expr=x in
         )
       } else {
         let mut count = 0;
-        let ret = (prefix.take(*len as usize))
+        let ret = (prefix.take(len as usize))
             .map(|x| { count+=1; x })
             .collect::<String>().into();
-        if count == *len {
+        if count == len {
           Ok(Literal::Str(ret).into())
         } else {
           RuntimeError::fail(
@@ -42,38 +53,22 @@ define_fn! {expr=x in
         }
       }
     }
-  }
-}
+  };
 
-define_fn! {expr=x in
   pub Find { haystack: OrcString, needle: OrcString } => {
     let haystack_graphs = haystack.as_str().graphemes(true);
     let found = iter_find(haystack_graphs, needle.as_str().graphemes(true));
     Ok(orchid_opt(found.map(|x| Literal::Uint(x as u64).into())))
-  }
-}
+  };
 
-define_fn! {expr=x in
   pub Split { s: OrcString, i: u64 } => {
     let mut graphs = s.as_str().graphemes(true);
-    let a = graphs.by_ref().take(*i as usize).collect::<String>();
+    let a = graphs.by_ref().take(i as usize).collect::<String>();
     let b = graphs.collect::<String>();
     Ok(tuple(vec![a.into(), b.into()]))
   }
 }
 
-define_fn! {
-  pub Len = |x| with_str(x, |s| {
-    Ok(Literal::Uint(s.graphemes(true).count() as u64).into())
-  })
-}
-
-define_fn! {
-  pub Size = |x| with_str(x, |s| {
-    Ok(Literal::Uint(s.as_bytes().len() as u64).into())
-  })
-}
-
 pub fn str(i: &Interner) -> ConstTree {
   ConstTree::tree([(
     i.i("str"),
diff --git a/src/utils/ddispatch.rs b/src/utils/ddispatch.rs
index dc60e89..a171a3d 100644
--- a/src/utils/ddispatch.rs
+++ b/src/utils/ddispatch.rs
@@ -5,10 +5,13 @@ use std::any::Any;
 /// A request for a value of an unknown type
 pub struct Request<'a>(&'a mut dyn Any);
 impl<'a> Request<'a> {
+  /// Checks whether a value of the given type would serve the request
   pub fn can_serve<T: 'static>(&self) -> bool { self.0.is::<Option<T>>() }
 
+  /// Serve a value if it's the correct type
   pub fn serve<T: 'static>(&mut self, value: T) { self.serve_with(|| value) }
 
+  /// Invoke the callback to serve the request only if the return type matches
   pub fn serve_with<T: 'static>(&mut self, provider: impl FnOnce() -> T) {
     if let Some(slot) = self.0.downcast_mut() {
       *slot = provider();
@@ -19,9 +22,11 @@ impl<'a> Request<'a> {
 /// Trait for objects that can respond to type-erased commands. This trait is
 /// a dependency of `Atomic` but the implementation can be left empty.
 pub trait Responder {
+  /// Try to provide as many types as we support
   fn respond(&self, _request: Request) {}
 }
 
+/// Request a specific contract type from a responder
 pub fn request<T: 'static>(responder: &(impl Responder + ?Sized)) -> Option<T> {
   let mut slot = None;
   responder.respond(Request(&mut slot));
diff --git a/src/utils/take_with_output.rs b/src/utils/take_with_output.rs
index c4778de..6ce49e7 100644
--- a/src/utils/take_with_output.rs
+++ b/src/utils/take_with_output.rs
@@ -1,3 +1,4 @@
+/// A variation on [take_mut::take] that allows the callback to return a value
 pub fn take_with_output<T, U>(src: &mut T, cb: impl FnOnce(T) -> (T, U)) -> U {
   take_mut::scoped::scope(|scope| {
     let (old, hole) = scope.take(src);
diff --git a/src/utils/thread_pool.rs b/src/utils/thread_pool.rs
index 7ccd32e..f360ead 100644
--- a/src/utils/thread_pool.rs
+++ b/src/utils/thread_pool.rs
@@ -168,9 +168,8 @@ impl<T: Task> Drop for ThreadPool<T> {
     self.data.stopping.store(true, Ordering::SeqCst);
     let mut rdv_point = self.data.rdv_point.lock().unwrap();
     if let Some(pending) = rdv_point.take() {
-      pending
-        .try_send(Message::Stop)
-        .expect("The channel is always removed before push")
+      // the worker has read the value of `stopping`
+      let _ = pending.send(Message::Stop);
     }
   }
 }