bugfix: , *sym printed as ,*sym.

We are lacking read/print consistency in the handling of
unquotes applied to symbols whose names begin with a star.

* lib.c (unquote_star_check): New static function.
(obj_print_impl): Use unquote_star check when printing
an unquote to determine whether a space is needed so
that the result doesn't read back as a ,* splice.

* txr.1: Change "should" to "must": the whitespace is
absolutely required in , *x*. Adding more discussion
as a dialect note.

2 files changed, 38 insertions, 5 deletions

diff --git a/lib.c b/lib.c
index c443d9b6..dd599d22 100644
--- a/lib.c
+++ b/lib.c
@@ -9514,6 +9514,15 @@ INLINE int circle_print_eligible(val obj)
   return is_ptr(obj) && (!symbolp(obj) || !symbol_package(obj));
 }
 
+static int unquote_star_check(val obj, val pretty)
+{
+  if (!obj || !symbolp(obj))
+    return 0;
+  if (car(obj->s.name) != chr('*'))
+    return 0;
+  return pretty || symbol_present(cur_package, obj);
+}
+
 val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
 {
   val ret = obj;
@@ -9556,7 +9565,10 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
         put_char(chr('^'), out);
         obj_print_impl(second(obj), out, pretty, ctx);
       } else if (sym == sys_unquote_s && two_elem) {
+        val arg = second(obj);
         put_char(chr(','), out);
+        if (unquote_star_check(arg, pretty))
+          put_char(chr(' '), out);
         obj_print_impl(second(obj), out, pretty, ctx);
       } else if (sym == sys_splice_s && two_elem) {
         put_string(lit(",*"), out);
@@ -9660,10 +9672,14 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
             unq = lit(". ,*");
 
           if (unq) {
-            d = cdr(iter);
+            val d = cdr(iter);
+            val ad = car(d);
+
             if (consp(d) && !cdr(d)) {
               put_string(unq, out);
-              obj_print_impl(car(d), out, pretty, ctx);
+              if (a == sys_unquote_s && unquote_star_check(ad, pretty))
+                put_char(chr(' '), out);
+              obj_print_impl(ad, out, pretty, ctx);
               put_char(closepar, out);
               break;
             }
diff --git a/txr.1 b/txr.1
index 255e90ec..0679a1b2 100644
--- a/txr.1
+++ b/txr.1
@@ -10357,7 +10357,7 @@ splice
 the value of
 .codn x* .
 In this situation, whitespace between the comma and the
-variable name should be used:
+variable name must be used:
 .codn ", *x*" .
 
 .meIP >> ,* expr
@@ -10376,14 +10376,31 @@ is evaluated to produce the list
 .codn "(6 8)" ,
 and this list is spliced into the quoted template.
 
-Dialect note: in other Lisp dialects, the equivalent syntax is usually
+.TP* "Dialect Notes:"
+
+In other Lisp dialects, like Scheme and ANSI Common Lisp, the equivalent syntax
+is usually
 .code ,@
 (comma at). The
 .code @
-character already has an assigned meaning, so
+character already has an assigned meaning in \*(TX, so
 .code *
 is used.
 
+However,
+.code *
+is also a character that may appear in a symbol name, which creates
+a potential for ambiguity. The syntax
+.code ,*abc
+denotes the application of the
+.code ,*
+splicing operator to the symbolic expression
+.codn abc ;
+to apply the ordinary non-splicing unquote to the symbol
+.codn *abc ,
+whitespace must be used:
+.codn ", *abc" .
+
 .NP* Quasiquoting non-List Objects
 Quasiquoting is supported over hash table and vector literals (see Vectors
 and Hashes below).  A hash table or vector literal can be quoted, like any