New function: seq-like.

* eval.c (zip_fun): Renamed to seq_like.
(zipv): Follow rename of zip_fun.
(eval_init): Register seq-like intrinsic.

* tests/seq.tl: Some tests for make-like and seq-like,
revealing a difference: make-like needs to be
rewritten to use seq_build.

* txr.1: Documented.

3 files changed, 49 insertions, 5 deletions

diff --git a/eval.c b/eval.c
index e8d57ff0..91220930 100644
--- a/eval.c
+++ b/eval.c
@@ -5864,7 +5864,7 @@ static val mapdov(val fun, varg lists)
   return map_common(lit("mapdo"), fun, lists, 0, mapdo);
 }
 
-static val zip_fun(val ziparg0, varg args)
+static val seq_like(val ziparg0, varg args)
 {
   seq_build_t bu;
   cnum index = 0;
@@ -5898,7 +5898,7 @@ static val zipv(varg zipargs)
       func = func_n0v(vectorv);
       break;
     default:
-      func = func_f0v(ziparg0, zip_fun);
+      func = func_f0v(ziparg0, seq_like);
       break;
     }
 
@@ -7813,6 +7813,7 @@ void eval_init(void)
   reg_fun(intern(lit("list-seq"), user_package), func_n1(list_seq));
   reg_fun(intern(lit("vec-seq"), user_package), func_n1(vec_seq));
   reg_fun(intern(lit("str-seq"), user_package), func_n1(str_seq));
+  reg_fun(intern(lit("seq-like"), user_package), func_n1v(seq_like));
   reg_fun(intern(lit("length"), user_package), length_f);
   reg_fun(intern(lit("len"), user_package), length_f);
   reg_fun(length_lt_s, func_n2(length_lt));
diff --git a/tests/012/seq.tl b/tests/012/seq.tl
index 171ad300..97549500 100644
--- a/tests/012/seq.tl
+++ b/tests/012/seq.tl
@@ -1598,3 +1598,17 @@
   [(wherequal 'c) '(a b c a b c)] (2 5)
   [(wherequal 3) '(3 3.0 b c a b c)] (0)
   [(wherequal 3) 0..9] (3))
+
+(mtest
+  (make-like '(1 2 3) "") (1 2 3)
+  (make-like '(#\a #\b #\c) "") "abc"
+  (make-like '(#\a #\b 3) "") :error
+  (make-like '(1 2 3) #()) #(1 2 3)
+  (make-like '(1 2 3) #b'') #b'010203')
+
+(mtest
+  (seq-like "" 1 2 3) (1 2 3)
+  (seq-like "" #\a #\b #\c) "abc"
+  (seq-like "" #\a #\b 3) (#\a #\b 3)
+  (seq-like #() 1 2 3) #(1 2 3)
+  (seq-like #b'' 1 2 3) #b'010203')
diff --git a/txr.1 b/txr.1
index d643ff7f..a5fb51fa 100644
--- a/txr.1
+++ b/txr.1
@@ -34408,24 +34408,28 @@ Additional objects that are not sequences are also iterable:
 numeric or character ranges, and numbers. Future revisions
 of the language may specify additional iterable objects.
 
-.coNP Function @ make-like
+.coNP Functions @ make-like and @ seq-like
 .synb
 .mets (make-like < list << object )
+.mets (seq-like < object << arg *)
 .syne
 .desc
 The
+.code make-like
+function's
 .meta list
 argument must be a list.  If
 .meta object
 is a sequence type,
 then
 .meta list
-is converted to the same type of sequence and returned.
+is converted to the same type of sequence, if possible, and returned.
 Otherwise the original
 .meta list
 is returned.
 
-Conversion is supported to string and vector type.
+Conversion is supported to string and vector type, plus
+additional types as follows.
 
 Conversion to a structure type is possible for structures. If
 .meta object
@@ -34465,6 +34469,31 @@ available, then
 takes that sequence in place of
 .metn object ,
 
+The
+.code seq-like
+function creates, if possible, a sequence of the same kind as
+.meta object
+populated by the remaining
+.meta arg
+values. If some of the
+.meta arg
+values are not suitable elements for a sequence of that type,
+then a list of those values is returned.
+
+The result of
+.code seq-like
+is consistent with what the
+.code make-like
+function would return if given a list of the
+.meta arg
+values as the
+.meta list
+argument. That is to say, the following equivalence holds:
+
+.verb
+  (make-like (list a0 a1 ...) o)  <->  (seq-like o a0 a1 ...)
+.brev
+
 Note: the
 .code make-like
 function is a helper which supports the development of