diff --git a/engine/src/ast/field_expr.rs b/engine/src/ast/field_expr.rs
index 44e4e87a..147b4362 100644
--- a/engine/src/ast/field_expr.rs
+++ b/engine/src/ast/field_expr.rs
@@ -799,9 +799,9 @@ mod tests {
     use crate::ast::logical_expr::LogicalExpr;
     use crate::execution_context::ExecutionContext;
     use crate::functions::{
-        FunctionArgKind, FunctionArgs, FunctionDefinition, FunctionDefinitionContext,
-        FunctionParam, FunctionParamError, SimpleFunctionDefinition, SimpleFunctionImpl,
-        SimpleFunctionOptParam, SimpleFunctionParam,
+        CompiledFunction, FunctionArgKind, FunctionArgs, FunctionDefinition,
+        FunctionDefinitionContext, FunctionParam, FunctionParamError, SimpleFunctionDefinition,
+        SimpleFunctionImpl, SimpleFunctionOptParam, SimpleFunctionParam,
     };
     use crate::lhs_types::{Array, Map};
     use crate::list_matcher::{ListDefinition, ListMatcher};
@@ -908,12 +908,7 @@ mod tests {
             &self,
             _: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
             _: Option<FunctionDefinitionContext>,
-        ) -> Box<
-            dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>>
-                + Sync
-                + Send
-                + 'static,
-        > {
+        ) -> CompiledFunction {
             Box::new(|args| {
                 let value_array = Array::try_from(args.next().unwrap().unwrap()).unwrap();
                 let keep_array = Array::try_from(args.next().unwrap().unwrap()).unwrap();
diff --git a/engine/src/ast/function_expr.rs b/engine/src/ast/function_expr.rs
index ef6deab7..c0656c91 100644
--- a/engine/src/ast/function_expr.rs
+++ b/engine/src/ast/function_expr.rs
@@ -8,7 +8,7 @@ use crate::ast::logical_expr::{LogicalExpr, UnaryOp};
 use crate::compiler::Compiler;
 use crate::filter::{CompiledExpr, CompiledValueExpr, CompiledValueResult};
 use crate::functions::{
-    ExactSizeChain, FunctionArgs, FunctionDefinition, FunctionDefinitionContext, FunctionParam,
+    CompiledFunction, ExactSizeChain, FunctionDefinition, FunctionDefinitionContext, FunctionParam,
     FunctionParamError,
 };
 use crate::lex::{Lex, LexError, LexErrorKind, LexResult, LexWith, expect, skip_space, span};
@@ -272,11 +272,9 @@ impl ValueExpr for FunctionCallExpr {
             let first = args.remove(0);
 
             #[inline(always)]
-            fn compute<'s, 'a, I: ExactSizeIterator<Item = CompiledValueResult<'a>>>(
+            fn compute<'a, I: ExactSizeIterator<Item = CompiledValueResult<'a>>>(
                 first: CompiledValueResult<'a>,
-                call: &(
-                     dyn for<'b> Fn(FunctionArgs<'_, 'b>) -> Option<LhsValue<'b>> + Sync + Send + 's
-                 ),
+                call: &CompiledFunction,
                 return_type: Type,
                 f: impl Fn(LhsValue<'a>) -> I,
             ) -> CompiledValueResult<'a> {
diff --git a/engine/src/functions/all.rs b/engine/src/functions/all.rs
index b78cb8e8..152aed41 100644
--- a/engine/src/functions/all.rs
+++ b/engine/src/functions/all.rs
@@ -1,10 +1,9 @@
 use crate::{
-    FunctionArgKind, FunctionArgs, FunctionDefinition, FunctionDefinitionContext, FunctionParam,
-    FunctionParamError, GetType, LhsValue, ParserSettings, Type,
+    CompiledFunction, FunctionArgKind, FunctionArgs, FunctionDefinition, FunctionDefinitionContext,
+    FunctionParam, FunctionParamError, GetType, LhsValue, ParserSettings, Type,
 };
 use std::iter::once;
 
-#[inline]
 fn all_impl<'a>(args: FunctionArgs<'_, 'a>) -> Option<LhsValue<'a>> {
     let arg = args.next().expect("expected 1 argument, got 0");
     if args.next().is_some() {
@@ -58,12 +57,11 @@ impl FunctionDefinition for AllFunction {
         (1, Some(0))
     }
 
-    fn compile<'s>(
-        &'s self,
+    fn compile(
+        &self,
         _: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
         _: Option<FunctionDefinitionContext>,
-    ) -> Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>
-    {
+    ) -> CompiledFunction {
         Box::new(all_impl)
     }
 }
diff --git a/engine/src/functions/any.rs b/engine/src/functions/any.rs
index a9f90b76..66199d33 100644
--- a/engine/src/functions/any.rs
+++ b/engine/src/functions/any.rs
@@ -1,10 +1,9 @@
 use crate::{
-    FunctionArgKind, FunctionArgs, FunctionDefinition, FunctionDefinitionContext, FunctionParam,
-    FunctionParamError, GetType, LhsValue, ParserSettings, Type,
+    CompiledFunction, FunctionArgKind, FunctionArgs, FunctionDefinition, FunctionDefinitionContext,
+    FunctionParam, FunctionParamError, GetType, LhsValue, ParserSettings, Type,
 };
 use std::iter::once;
 
-#[inline]
 fn any_impl<'a>(args: FunctionArgs<'_, 'a>) -> Option<LhsValue<'a>> {
     let arg = args.next().expect("expected 1 argument, got 0");
     if args.next().is_some() {
@@ -58,12 +57,11 @@ impl FunctionDefinition for AnyFunction {
         (1, Some(0))
     }
 
-    fn compile<'s>(
-        &'s self,
+    fn compile(
+        &self,
         _: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
         _: Option<FunctionDefinitionContext>,
-    ) -> Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>
-    {
+    ) -> CompiledFunction {
         Box::new(any_impl)
     }
 }
diff --git a/engine/src/functions/concat.rs b/engine/src/functions/concat.rs
index 1d493d93..681b099e 100644
--- a/engine/src/functions/concat.rs
+++ b/engine/src/functions/concat.rs
@@ -1,6 +1,7 @@
 use crate::{
-    Array, Bytes, ExpectedType, FunctionArgs, FunctionDefinition, FunctionDefinitionContext,
-    FunctionParam, FunctionParamError, GetType, LhsValue, ParserSettings, Type,
+    Array, Bytes, CompiledFunction, ExpectedType, FunctionArgs, FunctionDefinition,
+    FunctionDefinitionContext, FunctionParam, FunctionParamError, GetType, LhsValue,
+    ParserSettings, Type,
 };
 use std::iter::once;
 
@@ -19,6 +20,7 @@ impl ConcatFunction {
     }
 }
 
+#[inline]
 fn concat_array<'a>(accumulator: Array<'a>, args: FunctionArgs<'_, 'a>) -> Array<'a> {
     let mut args = args.flat_map(|arg| arg.ok());
     let Some(first) = args.next() else {
@@ -43,6 +45,7 @@ fn concat_array<'a>(accumulator: Array<'a>, args: FunctionArgs<'_, 'a>) -> Array
     Array::try_from_vec(val_type, vec).unwrap()
 }
 
+#[inline]
 fn concat_bytes<'a>(mut accumulator: Vec<u8>, args: FunctionArgs<'_, 'a>) -> Bytes<'a> {
     for arg in args {
         match arg {
@@ -54,6 +57,25 @@ fn concat_bytes<'a>(mut accumulator: Vec<u8>, args: FunctionArgs<'_, 'a>) -> Byt
     accumulator.into()
 }
 
+fn concat_impl<'a>(args: FunctionArgs<'_, 'a>) -> Option<LhsValue<'a>> {
+    while let Some(arg) = args.next() {
+        match arg {
+            Ok(LhsValue::Array(array)) => {
+                return Some(LhsValue::Array(concat_array(array, args)));
+            }
+            Ok(LhsValue::Bytes(bytes)) => {
+                return Some(LhsValue::Bytes(concat_bytes(
+                    bytes.into_owned().into(),
+                    args,
+                )));
+            }
+            Err(_) => (),
+            _ => unreachable!(),
+        }
+    }
+    None
+}
+
 pub(crate) const EXPECTED_TYPES: [ExpectedType; 2] =
     [ExpectedType::Array, ExpectedType::Type(Type::Bytes)];
 
@@ -90,30 +112,12 @@ impl FunctionDefinition for ConcatFunction {
         (2, None)
     }
 
-    fn compile<'s>(
-        &'s self,
+    fn compile(
+        &self,
         _: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
         _: Option<FunctionDefinitionContext>,
-    ) -> Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>
-    {
-        Box::new(|args| {
-            while let Some(arg) = args.next() {
-                match arg {
-                    Ok(LhsValue::Array(array)) => {
-                        return Some(LhsValue::Array(concat_array(array, args)));
-                    }
-                    Ok(LhsValue::Bytes(bytes)) => {
-                        return Some(LhsValue::Bytes(concat_bytes(
-                            bytes.into_owned().into(),
-                            args,
-                        )));
-                    }
-                    Err(_) => (),
-                    _ => unreachable!(),
-                }
-            }
-            None
-        })
+    ) -> CompiledFunction {
+        Box::new(concat_impl)
     }
 }
 
@@ -133,7 +137,7 @@ mod tests {
         .into_iter();
         assert_eq!(
             Some(LhsValue::Bytes(Bytes::Borrowed(b"helloworld"))),
-            CONCAT_FN.compile(&mut std::iter::empty(), None)(&mut args)
+            concat_impl(&mut args)
         );
     }
 
@@ -148,7 +152,7 @@ mod tests {
         .into_iter();
         assert_eq!(
             Some(LhsValue::Bytes(Bytes::Borrowed(b"helloworldhello2world2"))),
-            CONCAT_FN.compile(&mut std::iter::empty(), None)(&mut args)
+            concat_impl(&mut args)
         );
     }
 
@@ -159,7 +163,7 @@ mod tests {
         let mut args = vec![Ok(arg1), Ok(arg2)].into_iter();
         assert_eq!(
             Some(LhsValue::Array(Array::from_iter([1, 2, 3, 4, 5, 6]))),
-            CONCAT_FN.compile(&mut std::iter::empty(), None)(&mut args)
+            concat_impl(&mut args)
         );
     }
 
@@ -167,7 +171,7 @@ mod tests {
     #[should_panic]
     fn test_concat_function_bad_arg_type() {
         let mut args = vec![Ok(LhsValue::from(2))].into_iter();
-        CONCAT_FN.compile(&mut std::iter::empty(), None)(&mut args);
+        concat_impl(&mut args);
     }
 
     #[test]
diff --git a/engine/src/functions/mod.rs b/engine/src/functions/mod.rs
index 5129791a..2af36b10 100644
--- a/engine/src/functions/mod.rs
+++ b/engine/src/functions/mod.rs
@@ -373,6 +373,13 @@ impl std::fmt::Debug for FunctionDefinitionContext {
     }
 }
 
+/// A compiled function that can be called during filter execution.
+///
+/// Returned by [`FunctionDefinition::compile`] after a function call expression
+/// has been validated and compiled.
+pub type CompiledFunction =
+    Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>;
+
 /// Trait to implement function
 pub trait FunctionDefinition: Debug + Send + Sync {
     /// Custom context to store information during parsing
@@ -404,7 +411,7 @@ pub trait FunctionDefinition: Debug + Send + Sync {
         &self,
         params: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
         ctx: Option<FunctionDefinitionContext>,
-    ) -> Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>;
+    ) -> CompiledFunction;
 }
 
 // Simple function APIs
@@ -530,8 +537,7 @@ impl FunctionDefinition for SimpleFunctionDefinition {
         &self,
         params: &mut dyn ExactSizeIterator<Item = FunctionParam<'_>>,
         _: Option<FunctionDefinitionContext>,
-    ) -> Box<dyn for<'i, 'a> Fn(FunctionArgs<'i, 'a>) -> Option<LhsValue<'a>> + Sync + Send + 'static>
-    {
+    ) -> CompiledFunction {
         let params_count = params.len();
         let opt_params = &self.opt_params[(params_count - self.params.len())..];
         let implementation = self.implementation;
diff --git a/engine/src/lib.rs b/engine/src/lib.rs
index e9953d1d..e003eb9b 100644
--- a/engine/src/lib.rs
+++ b/engine/src/lib.rs
@@ -96,10 +96,10 @@ pub use self::filter::{
     CompiledExpr, CompiledOneExpr, CompiledValueExpr, CompiledVecExpr, Filter, FilterValue,
 };
 pub use self::functions::{
-    AllFunction, AnyFunction, ConcatFunction, FunctionArgInvalidConstantError, FunctionArgKind,
-    FunctionArgKindMismatchError, FunctionArgs, FunctionDefinition, FunctionDefinitionContext,
-    FunctionParam, FunctionParamError, SimpleFunctionArgKind, SimpleFunctionDefinition,
-    SimpleFunctionImpl, SimpleFunctionOptParam, SimpleFunctionParam,
+    AllFunction, AnyFunction, CompiledFunction, ConcatFunction, FunctionArgInvalidConstantError,
+    FunctionArgKind, FunctionArgKindMismatchError, FunctionArgs, FunctionDefinition,
+    FunctionDefinitionContext, FunctionParam, FunctionParamError, SimpleFunctionArgKind,
+    SimpleFunctionDefinition, SimpleFunctionImpl, SimpleFunctionOptParam, SimpleFunctionParam,
 };
 pub use self::lex::LexErrorKind;
 pub use self::lhs_types::{Array, Bytes, Map, MapIter, TypedArray, TypedMap};