diff --git a/context.go b/context.go
index 51e03b1..6c2df5f 100644
--- a/context.go
+++ b/context.go
@@ -34,6 +34,7 @@ type ExprFunc interface {
 // ----Expression Context
 type ExprContext interface {
 	Clone() ExprContext
+	Merge(ctx ExprContext)
 	GetVar(varName string) (value any, exists bool)
 	SetVar(varName string, value any)
 	UnsafeSetVar(varName string, value any)
diff --git a/function.go b/function.go
index c09028c..4605798 100644
--- a/function.go
+++ b/function.go
@@ -34,7 +34,7 @@ func (functor *baseFunctor) GetFunc() ExprFunc {
 	return functor.info
 }
 
-// ---- Linking with the functions of Go
+// ---- Linking with Go functions
 type golangFunctor struct {
 	baseFunctor
 	f FuncTemplate
@@ -48,18 +48,23 @@ func (functor *golangFunctor) Invoke(ctx ExprContext, name string, args []any) (
 	return functor.f(ctx, name, args)
 }
 
-// ---- Linking with the functions of Expr
+// ---- Linking with Expr functions
 type exprFunctor struct {
 	baseFunctor
 	params []string
 	expr   Expr
+	defCtx ExprContext
 }
 
-func newExprFunctor(e Expr, params []string) *exprFunctor {
-	return &exprFunctor{expr: e, params: params}
+func newExprFunctor(e Expr, params []string, ctx ExprContext) *exprFunctor {
+	return &exprFunctor{expr: e, params: params, defCtx: ctx}
 }
 
 func (functor *exprFunctor) Invoke(ctx ExprContext, name string, args []any) (result any, err error) {
+	if functor.defCtx != nil {
+		ctx.Merge(functor.defCtx)
+	}
+
 	for i, p := range functor.params {
 		if i < len(args) {
 			arg := args[i]
diff --git a/operand-func.go b/operand-func.go
index 4bafbad..f2b9b0a 100644
--- a/operand-func.go
+++ b/operand-func.go
@@ -108,11 +108,7 @@ func evalFuncDef(ctx ExprContext, self *term) (v any, err error) {
 		for _, param := range self.children {
 			paramList = append(paramList, param.source())
 		}
-		v = newExprFunctor(expr, paramList)
-		// v = &funcDefFunctor{
-		// 	params: paramList,
-		// 	expr:   expr,
-		// }
+		v = newExprFunctor(expr, paramList, ctx)
 	} else {
 		err = errors.New("invalid function definition: the body specification must be an expression")
 	}
diff --git a/simple-store.go b/simple-store.go
index 850be75..73e5805 100644
--- a/simple-store.go
+++ b/simple-store.go
@@ -12,29 +12,40 @@ import (
 
 type SimpleStore struct {
 	varStore  map[string]any
-	funcStore map[string]*funcInfo
+	funcStore map[string]ExprFunc
 }
 
 func NewSimpleStore() *SimpleStore {
 	ctx := &SimpleStore{
 		varStore:  make(map[string]any),
-		funcStore: make(map[string]*funcInfo),
+		funcStore: make(map[string]ExprFunc),
 	}
-	//ImportBuiltinsFuncs(ctx)
 	return ctx
 }
 
+func filterRefName(name string) bool  { return name[0] != '@' }
+func filterPrivName(name string) bool { return name[0] != '_' }
+
 func (ctx *SimpleStore) Clone() ExprContext {
 	return &SimpleStore{
-		varStore:  CloneFilteredMap(ctx.varStore, func(name string) bool { return name[0] != '@' }),
-		funcStore: CloneFilteredMap(ctx.funcStore, func(name string) bool { return name[0] != '@' }),
+		varStore:  CloneFilteredMap(ctx.varStore, filterRefName),
+		funcStore: CloneFilteredMap(ctx.funcStore, filterRefName),
+	}
+}
+
+func (ctx *SimpleStore) Merge(src ExprContext) {
+	for _, name := range src.EnumVars(filterRefName) {
+		ctx.varStore[name], _ = src.GetVar(name)
+	}
+	for _, name := range src.EnumFuncs(filterRefName) {
+		ctx.funcStore[name], _ = src.GetFuncInfo(name)
 	}
 }
 
 func varsCtxToBuilder(sb *strings.Builder, ctx ExprContext, indent int) {
 	sb.WriteString("vars: {\n")
 	first := true
-	for _, name := range ctx.EnumVars(func(name string) bool { return name[0] != '_' }) {
+	for _, name := range ctx.EnumVars(filterPrivName) {
 		if first {
 			first = false
 		} else {
@@ -164,7 +175,7 @@ func (ctx *SimpleStore) EnumFuncs(acceptor func(name string) (accept bool)) (fun
 
 func (ctx *SimpleStore) Call(name string, args []any) (result any, err error) {
 	if info, exists := ctx.funcStore[name]; exists {
-		functor := info.functor
+		functor := info.Functor()
 		result, err = functor.Invoke(ctx, name, args)
 	} else {
 		err = fmt.Errorf("unknown function %s()", name)