initial exception handling support

include/picrin/error.h

@@ -0,0 +1,18 @@
+#ifndef ERROR_H__
+#define ERROR_H__
+
+struct pic_error {
+  PIC_OBJECT_HEADER
+  enum pic_error_kind {
+    PIC_ERROR_OTHER,
+    PIC_ERROR_FILE,
+    PIC_ERROR_READ
+  } type;
+  char *msg;
+  pic_value irrs;
+};
+
+#define pic_error_p(v) (pic_type(v) == PIC_TT_ERROR)
+#define pic_error_ptr(v) ((struct pic_error *)pic_ptr(v))
+
+#endif

include/picrin/value.h

@@ -87,6 +87,7 @@ enum pic_tt {
   PIC_TT_BLOB,
   PIC_TT_PROC,
   PIC_TT_PORT,
+  PIC_TT_ERROR,
   PIC_TT_ENV,
   PIC_TT_CONT
 };