New variable integer-output-format to print integers as characters (bug#44155)

* doc/lispref/streams.texi (Output Variables): Add integer-output-format.

* src/print.c (print_object): In case of Lisp_Int, print integers
as characters when Vinteger_output_format is Qt, and in hex format
when Vinteger_output_format is 16.
(Vinteger_output_format): New variable.

* test/src/print-tests.el (print-integer-output-format): New test.

1 files changed, 32 insertions, 2 deletions

diff --git a/src/print.c b/src/print.c
index 53aa353769b..fa65a3cb268 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1908,8 +1908,31 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
     {
     case_Lisp_Int:
       {
-        int len = sprintf (buf, "%"pI"d", XFIXNUM (obj));
-        strout (buf, len, len, printcharfun);
+        int c;
+        intmax_t i;
+
+        if (EQ (Vinteger_output_format, Qt) && CHARACTERP (obj)
+            && (c = XFIXNUM (obj)))
+          {
+            printchar ('?', printcharfun);
+            if (escapeflag
+                && (c == ';' || c == '(' || c == ')' || c == '{' || c == '}'
+                    || c == '[' || c == ']' || c == '\"' || c == '\'' || c == '\\'))
+              printchar ('\\', printcharfun);
+            printchar (c, printcharfun);
+          }
+        else if (INTEGERP (Vinteger_output_format)
+                 && integer_to_intmax (Vinteger_output_format, &i)
+                 && i == 16 && !NILP (Fnatnump (obj)))
+          {
+            int len = sprintf (buf, "#x%"pI"x", (EMACS_UINT) XFIXNUM (obj));
+            strout (buf, len, len, printcharfun);
+          }
+        else
+          {
+            int len = sprintf (buf, "%"pI"d", XFIXNUM (obj));
+            strout (buf, len, len, printcharfun);
+          }
       }
       break;
 
@@ -2247,6 +2270,13 @@ A value of nil means to use the shortest notation
 that represents the number without losing information.  */);
   Vfloat_output_format = Qnil;
 
+  DEFVAR_LISP ("integer-output-format", Vinteger_output_format,
+               doc: /* The format used to print integers.
+When t, print characters from integers that represent a character.
+When a number 16, print non-negative integers in the hexadecimal format.
+Otherwise, by default print integers in the decimal format.  */);
+  Vinteger_output_format = Qnil;
+
   DEFVAR_LISP ("print-length", Vprint_length,
                doc: /* Maximum length of list to print before abbreviating.
 A value of nil means no limit.  See also `eval-expression-print-length'.  */);