refactor(rpn): extract 'd' operator into Delete method (pj)

Move the inline logic for the 'd' (delete variable) operator into a
proper Operations.Delete method, following the same registration pattern
as all other operators. Adds Delete to the StackOperator interface.

3 files changed, 22 insertions, 16 deletions

diff --git a/internal/rpn/operations_interfaces.go b/internal/rpn/operations_interfaces.go
index cc60db2..39edcad 100644
--- a/internal/rpn/operations_interfaces.go
+++ b/internal/rpn/operations_interfaces.go
@@ -53,6 +53,7 @@ type StackOperator interface {
 	Dup(stack *Stack) error
 	Swap(stack *Stack) error
 	Pop(stack *Stack) error
+	Delete(stack *Stack) error
 	Show(stack *Stack) (string, error)
 }
 
diff --git a/internal/rpn/operations_variables.go b/internal/rpn/operations_variables.go
index 49cab57..56bf9cd 100644
--- a/internal/rpn/operations_variables.go
+++ b/internal/rpn/operations_variables.go
@@ -65,6 +65,26 @@ func (o *Operations) DeleteVariable(name string) error {
 	return nil
 }
 
+// Delete pops a variable name from the stack and deletes that variable.
+// Usage: `name d`
+func (o *Operations) Delete(stack *Stack) error {
+	val, err := popStack(stack, "d")
+	if err != nil {
+		return err
+	}
+
+	var name string
+	switch v := val.(type) {
+	case *Symbol:
+		name = v.Name()
+	case *StringNum:
+		name = v.String()
+	default:
+		return fmt.Errorf("delete expects a variable name, got %T", val)
+	}
+	return o.DeleteVariable(name)
+}
+
 // ListVariables lists all variables.
 // Usage: `vars`
 func (o *Operations) ListVariables() (string, error) {
diff --git a/internal/rpn/operator_registry.go b/internal/rpn/operator_registry.go
index 605d1d7..80f5b05 100644
--- a/internal/rpn/operator_registry.go
+++ b/internal/rpn/operator_registry.go
@@ -68,22 +68,7 @@ func (r *OperatorRegistry) registerStackOperators(op OperatorProvider) {
 	r.registerStandardOperator("dup", func(stack *Stack) error { return op.Dup(stack) })
 	r.registerStandardOperator("swap", func(stack *Stack) error { return op.Swap(stack) })
 	r.registerStandardOperator("pop", func(stack *Stack) error { return op.Pop(stack) })
-	r.registerStandardOperator("d", func(stack *Stack) error {
-		val, err := popStack(stack, "d")
-		if err != nil {
-			return err
-		}
-		var name string
-		switch v := val.(type) {
-		case *Symbol:
-			name = v.Name()
-		case *StringNum:
-			name = v.String()
-		default:
-			return fmt.Errorf("delete expects a variable name, got %T", val)
-		}
-		return op.DeleteVariable(name)
-	})
+	r.registerStandardOperator("d", func(stack *Stack) error { return op.Delete(stack) })
 }
 
 // registerVariableOperators registers assignment and conversion operators.