new simpler GC

1 files changed, 50 insertions, 3 deletions

diff --git a/src/value.h b/src/value.h
index 3795486..1331d9d 100644
--- a/src/value.h
+++ b/src/value.h
@@ -1,9 +1,15 @@
 #ifndef IMB3_VALUE_H
 #define IMB3_VALUE_H
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 
+/**
+ * Declared "for real" in gc.h.
+ */
+struct object;
+
 struct value {
   uintptr_t bits;
 };
@@ -18,7 +24,7 @@ enum value_tag {
    * Fixnums, i.e. integers that are stored directly in the value rather than
    * being pointed to. This is a two-bit tag rather than a three-bit tag...
    */
-  VALUE_FIXNUM = 0b01,
+  TAG_FIXNUM = 0b01,
 
   /**
    * A builtin-object.
@@ -34,13 +40,54 @@ enum value_tag {
    * A standard-object, effectively a pair of a class and a slot array.
    */
   TAG_STANDARD_OBJECT = 0b110,
+
+  /**
+   * An tag that is _invalid_ for values, but may be used by the internals of
+   * the garbage collector.
+   */
+  TAG_GC_INTERNAL = 0b111,
 };
 
 /**
+ * The nil constant.
+ */
+static const struct value NIL = {.bits = 0};
+
+/**
  * Allocates a builtin-object with the given class and slot count.
  */
-struct value make_builtin_object(struct value class, size_t value_slot_count,
-                                 size_t untraced_slot_count);
+struct value alloc_builtin_object(struct value class, size_t value_slot_count,
+                                  size_t untraced_slot_count);
+
+/**
+ * Stores an intptr_t as a fixnum or a bignum.
+ */
+struct value integer_of_int(intptr_t);
+
+/**
+ * Returns the tag of a value.
+ */
+enum value_tag get_tag(struct value);
+
+/**
+ * Returns whether a value is a pointer.
+ */
+bool is_ptr(struct value);
+
+/**
+ * Tags a pointer.
+ */
+struct value tag_ptr(struct object *, enum value_tag);
+
+/**
+ * Untags a fixnum.
+ */
+intptr_t untag_fixnum(struct value);
+
+/**
+ * Untags a pointer.
+ */
+struct object *untag_ptr(struct value);
 
 /**
  * Bootstraps the class heirarchy. This should only be called once.