stream: clone stream before execution

internal/expr/functions/strings.go

@@ -15,6 +15,12 @@ type Lower struct {
 	Expr expr.Expr
 }
 
+func (s *Lower) Clone() expr.Expr {
+	return &Lower{
+		Expr: expr.Clone(s.Expr),
+	}
+}
+
 func (s *Lower) Eval(env *environment.Environment) (types.Value, error) {
 	val, err := s.Expr.Eval(env)
 	if err != nil {
@@ -55,6 +61,12 @@ type Upper struct {
 	Expr expr.Expr
 }
 
+func (s *Upper) Clone() expr.Expr {
+	return &Upper{
+		Expr: expr.Clone(s.Expr),
+	}
+}
+
 func (s *Upper) Eval(env *environment.Environment) (types.Value, error) {
 	val, err := s.Expr.Eval(env)
 	if err != nil {
@@ -101,6 +113,18 @@ type Trim struct {
 
 type TrimFunc func(string, string) string
 
+func (s *Trim) Clone() expr.Expr {
+	exprs := make([]expr.Expr, len(s.Expr))
+	for i := range s.Expr {
+		exprs[i] = expr.Clone(s.Expr[i])
+	}
+	return &Trim{
+		Expr:     exprs,
+		TrimFunc: s.TrimFunc,
+		Name:     s.Name,
+	}
+}
+
 func (s *Trim) Eval(env *environment.Environment) (types.Value, error) {
 	if len(s.Expr) > 2 {
 		return nil, fmt.Errorf("misuse of string function %v()", s.Name)