diff --git a/ast.go b/ast.go
index bf2215c..6d1bb35 100644
--- a/ast.go
+++ b/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"
 )
 
diff --git a/helpers.go b/helpers.go
index d524e2c..3fbdf68 100644
--- a/helpers.go
+++ b/helpers.go
@@ -14,7 +14,7 @@ func EvalString(ctx exprContext, source string) (result any, err error) {
 	parser := NewParser(ctx)
 
 	if tree, err = parser.parse(scanner); err == nil {
-		result, err = tree.eval(ctx)
+		result, err = tree.Eval(ctx)
 	}
 	return
 }
diff --git a/parser_test.go b/parser_test.go
index 7ba3368..dfa6421 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -65,7 +65,7 @@ func TestParser(t *testing.T) {
 		/* 39 */ {`(((1)))`, int64(1), nil},
 		/* 40 */ {`"uno_" + var2`, `uno_abc`, nil},
 		/* 41 */ {`0 || 0.0 && "hello"`, false, nil},
-		/* 42 */ {`"s" + true`, nil, errors.New(`left operand 's' [string] is not compatible with right operand 'true' [bool] with respect to operator "+"`)},
+		/* 42 */ {`"s" + true`, nil, errors.New(`left operand 's' [string] and right operand 'true' [bool] are not compatible with operator "+"`)},
 		/* 43 */ {`+false`, nil, errors.New(`prefix/postfix operator "+" do not support operand 'false' [bool]`)},
 		/* 44 */ {`false // very simple expression`, false, nil},
 		/* 45 */ {`1 + // Missing right operator`, nil, errors.New(`infix operator "+" requires two operands, got 1`)},
@@ -108,7 +108,7 @@ func TestParser(t *testing.T) {
 		/* 82 */ {`5 % 2`, int64(1), nil},
 		/* 83 */ {`5 % (-2)`, int64(1), nil},
 		/* 84 */ {`-5 % 2`, int64(-1), nil},
-		/* 85 */ {`5 % 2.0`, nil, errors.New(`left operand '5' [int64] is not compatible with right operand '2' [float64] with respect to operator "%"`)},
+		/* 85 */ {`5 % 2.0`, nil, errors.New(`left operand '5' [int64] and right operand '2' [float64] are not compatible with operator "%"`)},
 		/* 86 */ {`"a" < "b" AND NOT (2 < 1)`, true, nil},
 		/* 87 */ {`"a" < "b" AND NOT (2 == 1)`, true, nil},
 		/* 88 */ {`"a" < "b" AND ~ 2 == 1`, true, nil},
@@ -147,7 +147,7 @@ func TestParser(t *testing.T) {
 
 		good := true
 		if expr, gotErr = parser.parse(scanner); gotErr == nil {
-			gotResult, gotErr = expr.eval(ctx)
+			gotResult, gotErr = expr.Eval(ctx)
 		}
 
 		if gotResult != input.wantResult {
@@ -221,7 +221,7 @@ func NoTestListParser(t *testing.T) {
 
 		good := true
 		if expr, gotErr = parser.parse(scanner); gotErr == nil {
-			gotResult, gotErr = expr.eval(ctx)
+			gotResult, gotErr = expr.Eval(ctx)
 		}
 
 		if (gotResult == nil && input.wantResult != nil) || (gotResult != nil && input.wantResult == nil) {
diff --git a/term.go b/term.go
index 0352390..7703cef 100644
--- a/term.go
+++ b/term.go
@@ -188,7 +188,7 @@ func (self *term) compute(ctx exprContext) (v any, err error) {
 
 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
 	return fmt.Errorf(
-		"left operand '%v' [%T] is not compatible with right operand '%v' [%T] with respect to operator %q",
+		"left operand '%v' [%T] and right operand '%v' [%T] are not compatible with operator %q",
 		leftValue, leftValue,
 		rightValue, rightValue,
 		self.source())