From d1c8b93f7ba8376de9f1ddbf79c94537e394af52 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Fri, 4 Jan 2019 18:49:54 -0800
Subject: [PATCH] error msg for no pages

---
 pitfall/pitfall/page.rkt | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pitfall/pitfall/page.rkt b/pitfall/pitfall/page.rkt
index c18918d9..bd61be2d 100644
--- a/pitfall/pitfall/page.rkt
+++ b/pitfall/pitfall/page.rkt
@@ -8,7 +8,10 @@
 
 (provide (all-defined-out))
 
-(define (current-page doc) (car (pdf-pages doc)))
+(define (current-page doc)
+  (match (pdf-pages doc)
+    [(? pair? ps) (car ps)]
+    [_ (raise-argument-error 'current-page "no pages in pdf" doc)]))
 
 (define (add-content doc data)
   (page-write (current-page doc) data))