add nil stuff

Makefile

@@ -1,7 +1,7 @@
 all: build run
 
 build:
-	gcc -o bin/picrin -I./include src/main.c src/state.c
+	gcc -o bin/picrin -I./include src/main.c src/state.c src/gc.c
 
 clean:
 	rm bin/picrin

include/picrin/value.h

@@ -2,6 +2,7 @@
 #define VALUE_H__
 
 enum pic_vtype {
+  PIC_VTYPE_NIL,
   PIC_VTYPE_HEAP
 };
 
@@ -35,6 +36,7 @@ struct pic_symbol {
   char *name;
 };
 
+pic_value pic_nil_value();
 pic_value pic_obj_value(struct pic_object *obj);
 
 #endif

src/value.c

@@ -1,5 +1,15 @@
 #include "picrin.h"
 
+pic_value
+pic_nil_value()
+{
+  pic_value v;
+
+  v.vtype = PIC_VTYPE_NIL;
+  v.u.data = NULL;
+  return v;
+}
+
 pic_value
 pic_obj_value(struct pic_object *obj)
 {