let dictionary-ref return two values

docs/libs.rst

@@ -227,7 +227,7 @@ Note that dictionary is not a weak map; if you are going to make a highly memory
 
 - **(dictionary-ref dict key)**
 
-  Look up dictionary dict for a value associated with symbol key. If no object is associated with key, it will raise an error.
+  Look up dictionary dict for a value associated with symbol key. It returns two values: first is the associated value if exists, and second is a boolean of lookup result.
 
 - **(dictionary-set! dict key obj)**
 

piclib/picrin/macro.scm

@@ -27,12 +27,14 @@
     "memoize on symbols"
     (define cache (make-dictionary))
     (lambda (sym)
-      (if (dictionary-has? cache sym)
-          (dictionary-ref cache sym)
-          (begin
-            (define val (f sym))
-            (dictionary-set! cache sym val)
-            val))))
+      (call-with-values (lambda () (dictionary-ref cache sym))
+        (lambda (value exists)
+          (if exists
+              value
+              (begin
+                (define val (f sym))
+                (dictionary-set! cache sym val)
+                val))))))
 
   (define (identifier=? env1 sym1 env2 sym2)
 
@@ -117,9 +119,11 @@
                 (identifier=? mac-env x mac-env y))))
 
       (walk (lambda (sym)
-              (if (dictionary-has? icache* sym)
-                  (dictionary-ref icache* sym)
-                  (rename sym)))
+              (call-with-values (lambda () (dictionary-ref icache* sym))
+                (lambda (value exists)
+                  (if exists
+                      value
+                      (rename sym)))))
             (f (walk inject expr) inject compare))))
 
   (define (strip-syntax form)

src/dict.c

@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/dict.h"
+#include "picrin/cont.h"
 
 struct pic_dict *
 pic_dict_new(pic_state *pic)
@@ -92,7 +93,11 @@ pic_dict_dict_ref(pic_state *pic)
 
   pic_get_args(pic, "dm", &dict, &key);
 
-  return pic_dict_ref(pic, dict , key);
+  if (pic_dict_has(pic, dict, key)) {
+    return pic_values2(pic, pic_dict_ref(pic, dict , key), pic_true_value());
+  } else {
+    return pic_values2(pic, pic_none_value(), pic_false_value());
+  }
 }
 
 static pic_value
@@ -109,17 +114,6 @@ pic_dict_dict_set(pic_state *pic)
   return pic_none_value();
 }
 
-static pic_value
-pic_dict_dict_has_p(pic_state *pic)
-{
-  struct pic_dict *dict;
-  pic_sym key;
-
-  pic_get_args(pic, "dm", &dict, &key);
-
-  return pic_bool_value(pic_dict_has(pic, dict, key));
-}
-
 static pic_value
 pic_dict_dict_del(pic_state *pic)
 {
@@ -166,7 +160,6 @@ pic_init_dict(pic_state *pic)
   pic_deflibrary (pic, "(picrin dictionary)") {
     pic_defun(pic, "make-dictionary", pic_dict_dict);
     pic_defun(pic, "dictionary?", pic_dict_dict_p);
-    pic_defun(pic, "dictionary-has?", pic_dict_dict_has_p);
     pic_defun(pic, "dictionary-ref", pic_dict_dict_ref);
     pic_defun(pic, "dictionary-set!", pic_dict_dict_set);
     pic_defun(pic, "dictionary-delete", pic_dict_dict_del);