Expr functions now act as closures

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]