diff --git a/engine/src/execution_context.rs b/engine/src/execution_context.rs
index a47ab632..62f32cd8 100644
--- a/engine/src/execution_context.rs
+++ b/engine/src/execution_context.rs
@@ -1,7 +1,7 @@
 use crate::{
     scheme::{Field, List, Scheme, SchemeMismatchError},
     types::{GetType, LhsValue, LhsValueSeed, Type, TypeMismatchError},
-    ListMatcher,
+    ListMatcher, UnknownFieldError,
 };
 use serde::de::{self, DeserializeSeed, Deserializer, MapAccess, Visitor};
 use serde::ser::{SerializeMap, SerializeSeq, Serializer};
@@ -16,11 +16,15 @@ use thiserror::Error;
 pub enum SetFieldValueError {
     /// An error that occurs when trying to assign a value of the wrong type to a field.
     #[error("{0}")]
-    TypeMismatchError(#[source] TypeMismatchError),
+    TypeMismatch(#[source] TypeMismatchError),
 
     /// An error that occurs when trying to set the value of a field from a different scheme.
     #[error("{0}")]
-    SchemeMismatchError(#[source] SchemeMismatchError),
+    SchemeMismatch(#[source] SchemeMismatchError),
+
+    /// An error that occurs when specifying an unknown field name.
+    #[error("{0}")]
+    UnknownField(#[source] UnknownFieldError),
 }
 
 /// An error that occurs when previously defined list gets redefined.
@@ -82,7 +86,7 @@ impl<'e, U> ExecutionContext<'e, U> {
         value: V,
     ) -> Result<Option<LhsValue<'e>>, SetFieldValueError> {
         if !std::ptr::eq(self.scheme, field.scheme()) {
-            return Err(SetFieldValueError::SchemeMismatchError(SchemeMismatchError));
+            return Err(SetFieldValueError::SchemeMismatch(SchemeMismatchError));
         }
         let value = value.into();
 
@@ -92,7 +96,32 @@ impl<'e, U> ExecutionContext<'e, U> {
         if field_type == value_type {
             Ok(self.values[field.index()].replace(value))
         } else {
-            Err(SetFieldValueError::TypeMismatchError(TypeMismatchError {
+            Err(SetFieldValueError::TypeMismatch(TypeMismatchError {
+                expected: field_type.into(),
+                actual: value_type,
+            }))
+        }
+    }
+
+    /// Sets a runtime value for a given field name.
+    pub fn set_field_value_from_name<'v: 'e, V: Into<LhsValue<'v>>>(
+        &mut self,
+        name: &str,
+        value: V,
+    ) -> Result<Option<LhsValue<'e>>, SetFieldValueError> {
+        let field = self
+            .scheme
+            .get_field(name)
+            .map_err(SetFieldValueError::UnknownField)?;
+        let value = value.into();
+
+        let field_type = field.get_type();
+        let value_type = value.get_type();
+
+        if field_type == value_type {
+            Ok(self.values[field.index()].replace(value))
+        } else {
+            Err(SetFieldValueError::TypeMismatch(TypeMismatchError {
                 expected: field_type.into(),
                 actual: value_type,
             }))
@@ -138,6 +167,12 @@ impl<'e, U> ExecutionContext<'e, U> {
         &*self.list_matchers[list.index()]
     }
 
+    /// Get the list matcher object for the specified type.
+    pub fn get_list_matcher_from_type(&self, ty: &Type) -> Option<&dyn ListMatcher> {
+        let list = self.scheme.get_list(ty)?;
+        Some(&*self.list_matchers[list.index()])
+    }
+
     /// Get the list matcher object for the specified list type.
     pub fn get_list_matcher_mut(&mut self, list: List<'_>) -> &mut dyn ListMatcher {
         assert!(self.scheme() == list.scheme());
@@ -145,6 +180,12 @@ impl<'e, U> ExecutionContext<'e, U> {
         &mut *self.list_matchers[list.index()]
     }
 
+    /// Get the list matcher object for the specified type.
+    pub fn get_list_matcher_mut_from_type(&mut self, ty: &Type) -> Option<&mut dyn ListMatcher> {
+        let list = self.scheme.get_list(ty)?;
+        Some(&mut *self.list_matchers[list.index()])
+    }
+
     /// Get immutable reference to user data stored in
     /// this execution context with [`ExecutionContext::new_with`].
     #[inline]
@@ -285,18 +326,18 @@ impl<'de, U> DeserializeSeed<'de> for &mut ExecutionContext<'de, U> {
                             .map_err(|_| de::Error::custom(format!("unknown field: {key}")))?;
                         let value = access
                             .next_value_seed::<LhsValueSeed<'_>>(LhsValueSeed(&field.get_type()))?;
-                        let field = self
-                            .0
-                            .scheme()
-                            .get_field(&key)
-                            .map_err(|_| de::Error::custom(format!("unknown field: {key}")))?;
-                        self.0.set_field_value(field, value).map_err(|e| match e {
-                            SetFieldValueError::TypeMismatchError(e) => de::Error::custom(format!(
-                                "invalid type: {:?}, expected {:?}",
-                                e.actual, e.expected
-                            )),
-                            SetFieldValueError::SchemeMismatchError(_) => unreachable!(),
-                        })?;
+                        self.0
+                            .set_field_value_from_name(&key, value)
+                            .map_err(|e| match e {
+                                SetFieldValueError::UnknownField(UnknownFieldError) => {
+                                    de::Error::custom(format!("unknown field name `{key}`",))
+                                }
+                                SetFieldValueError::TypeMismatch(e) => de::Error::custom(format!(
+                                    "invalid type: {:?}, expected {:?}",
+                                    e.actual, e.expected
+                                )),
+                                SetFieldValueError::SchemeMismatch(_) => unreachable!(),
+                            })?;
                     }
                 }
 
@@ -361,7 +402,7 @@ fn test_field_value_type_mismatch() {
 
     assert_eq!(
         ctx.set_field_value(scheme.get_field("foo").unwrap(), LhsValue::Bool(false)),
-        Err(SetFieldValueError::TypeMismatchError(TypeMismatchError {
+        Err(SetFieldValueError::TypeMismatch(TypeMismatchError {
             expected: Type::Int.into(),
             actual: Type::Bool,
         }))
@@ -378,9 +419,7 @@ fn test_scheme_mismatch() {
 
     assert_eq!(
         ctx.set_field_value(scheme2.get_field("foo").unwrap(), LhsValue::Bool(false)),
-        Err(SetFieldValueError::SchemeMismatchError(
-            SchemeMismatchError {}
-        ))
+        Err(SetFieldValueError::SchemeMismatch(SchemeMismatchError {}))
     );
 }