diff --git a/ast.go b/ast.go
index 6319187..627984b 100644
--- a/ast.go
+++ b/ast.go
@@ -10,7 +10,6 @@ import (
 
 type Expr interface {
 	Eval(ctx ExprContext) (result any, err error)
-	eval(ctx ExprContext, preset bool) (result any, err error)
 	String() string
 }
 
@@ -106,16 +105,10 @@ func (self *ast) Finish() {
 }
 
 func (self *ast) Eval(ctx ExprContext) (result any, err error) {
-	return self.eval(ctx, true)
-}
-
-func (self *ast) eval(ctx ExprContext, preset bool) (result any, err error) {
 	self.Finish()
 
 	if self.root != nil {
-		if preset {
-			initDefaultVars(ctx)
-		}
+		initDefaultVars(ctx)
 		if self.forest != nil {
 			for _, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {
diff --git a/control.go b/control.go
index 0e6c7eb..028ca58 100644
--- a/control.go
+++ b/control.go
@@ -8,10 +8,11 @@ import "strings"
 
 // Preset control variables
 const (
-	ControlLastResult   = "last"
-	ControlBoolShortcut = "_bool_shortcut"
-	ControlImportPath   = "_import_path"
-	ControlPluginPath   = "_plugin_path"
+	ControlPreset        = "_preset"
+	ControlLastResult    = "last"
+	ControlBoolShortcut  = "_bool_shortcut"
+	ControlSearchPath    = "_search_path"
+	ControlParentContext = "_parent_context"
 )
 
 // Other control variables
@@ -21,30 +22,61 @@ const (
 
 // Initial values
 const (
-	init_import_path = "~/.local/lib/go-pkg/expr/sources:/usr/local/lib/go-pkg/expr/sources:/usr/lib/go-pkg/expr/sources"
-	init_plugin_path = "~/.local/lib/go-pkg/expr/plugins:/usr/local/lib/go-pkg/expr/plugins:/usr/lib/go-pkg/expr/plugins"
+	init_search_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
 )
 
 func initDefaultVars(ctx ExprContext) {
+	if _, exists := ctx.GetVar(ControlPreset); exists {
+		return
+	}
+	ctx.SetVar(ControlPreset, true)
 	ctx.SetVar(ControlBoolShortcut, true)
-	ctx.SetVar(ControlImportPath, init_import_path)
-	ctx.SetVar(ControlPluginPath, init_plugin_path)
+	ctx.SetVar(ControlSearchPath, init_search_path)
 }
 
-func enable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, true)
-	} else {
-		ctx.SetVar("_"+name, true)
+func CtrlEnable(ctx ExprContext, name string) (currentStatus bool) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
 	}
+	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, true)
+	return currentStatus
 }
 
-func disable(ctx ExprContext, name string) {
-	if strings.HasPrefix(name, "_") {
-		ctx.SetVar(name, false)
-	} else {
-		ctx.SetVar("_"+name, false)
+func CtrlDisable(ctx ExprContext, name string) (currentStatus bool) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
 	}
+	if v, exists := ctx.GetVar(name); exists && IsBool(v) {
+		currentStatus, _ = v.(bool)
+	}
+
+	ctx.SetVar(name, false)
+	return currentStatus
+}
+
+func CtrlSet(ctx ExprContext, name string, newValue any) (currentValue any) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	currentValue, _ = ctx.GetVar(name)
+
+	ctx.SetVar(name, newValue)
+	for parent := ctx.GetParent(); parent != nil; parent = parent.GetParent() {
+		parent.SetVar(name, newValue)
+	}
+	return currentValue
+}
+
+func CtrlGet(ctx ExprContext, name string) (currentValue any) {
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+	currentValue, _ = ctx.GetVar(name)
+	return currentValue
 }
 
 func isEnabled(ctx ExprContext, name string) (status bool) {