patch 8.0.0075
Problem:    Using number for exception type lacks type checking.
Solution:   Use an enum.
diff --git a/src/structs.h b/src/structs.h
index 7a4d7fb..31accea 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -815,13 +815,23 @@
 };
 
 /*
+ * The exception types.
+ */
+typedef enum
+{
+    ET_USER,		/* exception caused by ":throw" command */
+    ET_ERROR,		/* error exception */
+    ET_INTERRUPT	/* interrupt exception triggered by Ctrl-C */
+} except_type_T;
+
+/*
  * Structure describing an exception.
  * (don't use "struct exception", it's used by the math library).
  */
 typedef struct vim_exception except_T;
 struct vim_exception
 {
-    int			type;		/* exception type */
+    except_type_T	type;		/* exception type */
     char_u		*value;		/* exception value */
     struct msglist	*messages;	/* message(s) causing error exception */
     char_u		*throw_name;	/* name of the throw point */
@@ -830,13 +840,6 @@
 };
 
 /*
- * The exception types.
- */
-#define ET_USER		0	/* exception caused by ":throw" command */
-#define ET_ERROR	1	/* error exception */
-#define ET_INTERRUPT	2	/* interrupt exception triggered by Ctrl-C */
-
-/*
  * Structure to save the error/interrupt/exception state between calls to
  * enter_cleanup() and leave_cleanup().  Must be allocated as an automatic
  * variable by the (common) caller of these functions.