core: Support keywords.

* display.c (display): Handle keyword.
* mes.c (type_t): Add KEYWORD.
  (eq_p): Handle it.
  (make_keyword): New function.
* reader.c (lookup): Use it.
* type.c (keyword_p): New function.
* NEWS: Update.

NEWS

@@ -16,6 +16,8 @@ Please send Mes bug reports to janneke@gnu.org.
 The C-reader needs only support reading of words and lists
 (s-expressions), line-comments.  Quoting, characters, strings,
 block-comments are all handled by the Scheme reader later.
+** Language
+*** Keywords are supported.
 * Changes in 0.3 since 0.2
 ** Core
 *** Number-based rather than pointer-based cells.

display.c

@@ -127,6 +127,8 @@ display_helper (FILE* f, SCM x, bool cont, char const *sep, bool quote)
         break;
       }
     case BROKEN_HEART: fprintf (f, "<3"); break;
+    case KEYWORD:
+      fprintf (f, "#:");
     default:
       if (STRING (x))
         {

mes.c

@@ -44,7 +44,7 @@ int MAX_ARENA_SIZE = 20000000;
 int GC_SAFETY = 100;
 
 typedef int SCM;
-enum type_t {CHAR, FUNCTION, MACRO, NUMBER, PAIR, SPECIAL, STRING, SYMBOL, REF, VALUES, VECTOR, BROKEN_HEART};
+enum type_t {CHAR, FUNCTION, KEYWORD, MACRO, NUMBER, PAIR, SPECIAL, STRING, SYMBOL, REF, VALUES, VECTOR, BROKEN_HEART};
 typedef SCM (*function0_t) (void);
 typedef SCM (*function1_t) (SCM);
 typedef SCM (*function2_t) (SCM, SCM);
@@ -250,6 +250,8 @@ SCM
 eq_p (SCM x, SCM y)
 {
   return (x == y
+          || ((TYPE (x) == KEYWORD && TYPE (y) == KEYWORD
+               && STRING (x) == STRING (y)))
           || (TYPE (x) == CHAR && TYPE (y) == CHAR
               && VALUE (x) == VALUE (y))
           || (TYPE (x) == NUMBER && TYPE (y) == NUMBER
@@ -676,6 +678,15 @@ make_function (SCM name, SCM id, SCM arity)
   return make_cell (tmp_num3, name, tmp_num4);
 }
 
+SCM
+make_keyword (SCM s)
+{
+  SCM x = internal_lookup_symbol (s);
+  x = x ? x : internal_make_symbol (s);
+  g_cells[tmp_num].value = KEYWORD;
+  return make_cell (tmp_num, STRING (x), 0);
+}
+
 SCM
 make_macro (SCM name, SCM x)
 {
@@ -932,7 +943,8 @@ gc_loop (SCM scan)
 {
   while (scan < g_free.value)
     {
-      if (NTYPE (scan) == MACRO
+      if (NTYPE (scan) == KEYWORD
+          || NTYPE (scan) == MACRO
           || NTYPE (scan) == PAIR
           || NTYPE (scan) == REF
           || scan == 1 // null

reader.c

@@ -224,6 +224,8 @@ lookup (SCM s, SCM a)
     if (p == cell_nil) return make_number (n * sign);
   }
 
+  if (VALUE (car (s)) == '#' && VALUE (cadr (s)) == ':') return make_keyword (cddr (s));
+
   SCM x = internal_lookup_symbol (s);
   if (x) return x;
 

string.c

@@ -110,3 +110,17 @@ symbol_to_string (SCM x)
   assert (TYPE (x) == SYMBOL);
   return make_string (STRING (x));
 }
+
+SCM
+keyword_to_symbol (SCM x)
+{
+  assert (TYPE (x) == KEYWORD);
+  return make_symbol (STRING (x));
+}
+
+SCM
+symbol_to_keyword (SCM x)
+{
+  assert (TYPE (x) == SYMBOL);
+  return make_keyword (STRING (x));
+}

type.c

@@ -26,6 +26,12 @@ char_p (SCM x)
   return TYPE (x) == CHAR ? cell_t : cell_f;
 }
 
+SCM
+keyword_p (SCM x)
+{
+  return TYPE (x) == KEYWORD ? cell_t : cell_f;
+}
+
 SCM
 macro_p (SCM x)
 {