ast: now supports espression forest (multi expressions)

ast.go

@@ -13,6 +13,7 @@ import (
 //-------- ast
 
 type ast struct {
+	forest []*term
 	root *term
 }
 
@@ -20,6 +21,16 @@ func NewAst() *ast {
 	return &ast{}
 }
 
+func (self *ast) ToForest() {
+	if self.root != nil {
+		if self.forest == nil {
+			self.forest = make([]*term, 0)
+		}
+		self.forest = append(self.forest, self.root)
+		self.root = nil
+	}
+}
+
 func (self *ast) String() string {
 	var sb strings.Builder
 	if self.root == nil {
@@ -77,10 +88,31 @@ func (self *ast) insert(tree, node *term) (root *term, err error) {
 	return
 }
 
-func (self *ast) eval(ctx exprContext) (result any, err error) {
+func (self *ast) Finish() {
+        if self.root == nil && self.forest != nil && len(self.forest) >= 1 {
+                self.root = self.forest[len(self.forest)-1]
+                self.forest = self.forest[0:len(self.forest) - 1]
+        }
+}
+
+func (self *ast) Eval(ctx exprContext) (result any, err error) {
+	self.Finish()
+
 	if self.root != nil {
 		initDefaultVars(ctx)
-		result, err = self.root.compute(ctx)
+		if self.forest != nil {
+			for i, root := range self.forest {
+				if result, err = root.compute(ctx); err == nil {
+					ctx.SetValue(preset_last_result, result)
+				} else {
+					err = fmt.Errorf("error in expression nr %d: %v", i+1, err)
+					break
+				}
+			}
+		}
+		if err == nil {
+			result, err = self.root.compute(ctx)
+		}
 	} else {
 		err = errors.New("empty expression")
 	}
@@ -89,6 +121,7 @@ func (self *ast) eval(ctx exprContext) (result any, err error) {
 
 // Preset variables
 const (
+	preset_last_result = "_last"
 	preset_bool_shortcut = "_bool_shortcut"
 )