From: Mark Thom <markjordanthom@gmail.com>
Date: Wed, 30 Mar 2022 00:39:45 +0000 (-0600)
Subject: fix dif/2 crash (#1378)
X-Git-Tag: v0.9.1~86
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=c490d818fbf64e56f1dffe4342f5fcf87340d4d5;p=scryer-prolog.git

fix dif/2 crash (#1378)
---

diff --git a/src/machine/machine_state_impl.rs b/src/machine/machine_state_impl.rs
index 7a90f88f..f5789878 100644
--- a/src/machine/machine_state_impl.rs
+++ b/src/machine/machine_state_impl.rs
@@ -1621,10 +1621,13 @@ impl MachineState {
                         );
 
                         let c2 = stalled_iter.heap[l];
-                        let c1 = string_iter.chars().next().unwrap();
+                        let c1 = match string_iter.chars().next() {
+                            Some(c) => char_as_cell!(c),
+                            None => string_iter.focus,
+                        };
 
                         pdl.push(c2);
-                        pdl.push(char_as_cell!(c1));
+                        pdl.push(c1);
 
                         None
                     }