diff --git a/makefiles/etc/todo.mk b/makefiles/etc/todo.mk
new file mode 100644
index 0000000..31fc736
--- /dev/null
+++ b/makefiles/etc/todo.mk
@@ -0,0 +1,21 @@
+## -----------------------------------------------------------------------
+## Intent: Cast value into a boolean string.
+## NOTE: : Careful with line comment placement, when octolthorp is indented
+##         in a makefile return value will have whitespace appended.
+## -----------------------------------------------------------------------
+boolean = $(if $(strip $($(1))),false,true)# trailing whitespace is bad here
+
+## -----------------------------------------------------------------------
+## Intet: Negate input value for conditional use.
+##   Return success when input value is null.
+## Usage:
+##   $(info ** defined[true]  = $(call not,value))
+##   $(info ** defined[false] = $(call not,$(null)))
+##   $(if $(call not,varname),$(error varname= is not set))
+## -----------------------------------------------------------------------
+not = $(strip \
+  $(foreach true-false\
+    ,$(info true-false=$(true-false))$(strip $(call boolean,$(1)))\
+      $(subst true,$(null),$(true-false))\
+  )\
+)