Added style #19. True story.

19-defensive/README.md

@@ -0,0 +1,17 @@
+Style #19
+==============================
+
+Constraints:
+
+- Every single procedure and function checks the sanity of its
+  arguments and either returns something sensible when the arguments
+  are unreasonable or assigns them reasonable values
+
+- All code blocks check for all possible errors and escape the block
+  when things go wrong
+
+Possible names:
+
+- Defensive
+- Pessimistic
+- Never trust the caller nor the callee