1 files changed, 16 insertions, 1 deletions
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index b4b65883d..d4e179008 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -197,7 +197,22 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
     if (!pos)
         str << "undefined position";
     else
-        str << (format(ANSI_BOLD "%1%" ANSI_NORMAL ":%2%:%3%") % (string) pos.file % pos.line % pos.column).str();
+    { 
+        auto f = format(ANSI_BOLD "%1%" ANSI_NORMAL ":%2%:%3%");
+        switch (pos.origin) { 
+            case foFile:
+                f % (string) pos.file; 
+                break;
+            case foStdin:
+            case foString:
+                f % "(string)";
+                break;
+            default:
+                throw Error("unhandled Pos origin!");
+        }
+        str << (f % pos.line % pos.column).str();
+    }
+
     return str;
 }