* lib.c (make_like): Bugfix. (make-like nil "abc")

must return the empty string, not nil. Only
lists of non-characters fail to convert to a string.
Since programs may depend on the hitherto wrong,
undocumented behavior, this is made subject to
compatibility.

* txr.1: Added compatibility note.

3 files changed, 27 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 52c8a16f..4e01eb8b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
 2015-01-11  Kaz Kylheku  <kaz@kylheku.com>
 
+	* lib.c (make_like): Bugfix. (make-like nil "abc")
+	must return the empty string, not nil. Only
+	lists of non-characters fail to convert to a string.
+	Since programs may depend on the hitherto wrong,
+	undocumented behavior, this is made subject to
+	compatibility.
+
+	* txr.1: Added compatibility note.
+
+2015-01-11  Kaz Kylheku  <kaz@kylheku.com>
+
 	* eval.c (merge_wrap): Make generic over sequences.
 
 	* txr.1: Update documentation for merge function.
diff --git a/lib.c b/lib.c
index a6f01a66..41a9c29f 100644
--- a/lib.c
+++ b/lib.c
@@ -504,6 +504,10 @@ val make_like(val list, val thatobj)
     case STR:
     case LIT:
     case LSTR:
+      if (!opt_compat || opt_compat > 101) {
+        if (!cdr(list))
+          return null_string;
+      }
       if (is_chr(car(list)))
         return cat_str(list, nil);
       break;
diff --git a/txr.1 b/txr.1
index 8b329d7b..fb1b3c37 100644
--- a/txr.1
+++ b/txr.1
@@ -26443,6 +26443,18 @@ can be emulated is \*(TX 97.
 Here are values which have a special meaning as arguments to the
 .code -C
 option, along with a description of what behaviors are affected:
+.IP 101
+Up to \*(TX 101, the
+.code make-like
+function incorrectly returned
+.code nil
+when converting the empty list
+.code nil
+to string type. This affects numerous generic sequence functions,
+causing their result to be
+.code nil
+instead of an empty string.
+
 .IP 100
 Up to \*(TX 100, the
 .code split-str