Makefile: Add removed target

Lets you list out what files were removed from OLD to NEW generations. Note
automatically done to remove files as I consider that the job of the user.

While here, added a function check_defined to let me check if a variable is
defined or not and if not bail.

Updated the option target to use this function as well as the removed target
where I needed it for.

Makefile

@@ -1,19 +1,31 @@
 # Makefile is here to make it possible to use this whole shebang
 # outside of emacs.
+#
+# TODO: wrap this stuff into a script maybe?
 DEST:=$(HOME)
-LAST:=$(shell cat .last || echo 0)
-NEXT:=$(shell l=$(LAST); ((l=l+1)); echo $$l)
+LAST!=cat .last || echo 0
+NEXT!=l=$(LAST); ((l=l+1)); echo $$l
 NEXTGEN:=$(PWD)/generation/$(NEXT)
 LASTGEN:=$(PWD)/generation/$(LAST)
-TANGLERS:=$(shell ls -d *.org)
+TANGLERS:=$(wildcard *.org)
 GEN:=$(LAST)
 OPTS:=
 # OSX uses scutil --get ComputerName
 # uname -n && hostname -s can return dhcp addresses
 # which aren't stable.
-HOST=$(shell echo "$$(scutil --get ComputerName || uname -n)")
+HOST!=scutil --get ComputerName || uname -n
 USEROPTS:=$(OPTS):$(HOST)
-NAME:=default
+
+# Make it easier to check if a variable is defined or not
+# params:
+# variable name
+# optional message to print if variable is not set
+check_defined = \
+    $(strip $(foreach 1,$1, \
+        $(call __check_defined,$1,$(strip $(value 2)))))
+__check_defined = \
+    $(if $(value $1),, \
+      $(error Undefined variable $1$(if $2, ($2))))
 
 INSTALLDIRS=tmp $(NEXTGEN) $(LASTGEN) generation/$(GEN)
 
@@ -25,8 +37,6 @@ $(INSTALLDIRS):
 generation: $(NEXTGEN) $(LASTGEN) tmp
 	cd tmp && cp -av . $(NEXTGEN)
 
-check:
-
 diff: generation/$(GEN)
 	./ddiff $(PWD)/generation/$(GEN) $(DEST)
 
@@ -50,6 +60,15 @@ copy:
 tangle: tmp
 	USEROPTS=$(USEROPTS) /usr/bin/env emacs --script ./etangle $(TANGLERS)
 
+# TODO: is this gnu diff output... only or not? note: wip until i've
+# tested on bsd make etc...
+
+.PHONY: removed
+removed:
+	$(call check_defined, OLD, generation to compare removed files against)
+	$(call check_defined, NEW, generation to compare removed files to)
+	@diff -bur generation/$(OLD) generation/$(NEW) 2>&1 | grep 'Only in generation/'$(OLD) | sed -e 's|Only in ||' -e 's|.*[:] ||'
+
 clean:
 	-rm -fr tmp
 
@@ -58,5 +77,6 @@ nuke: clean
 
 .PHONY: option
 option:
+	$(call check_defined, NAME, predicate NAME to define in option files. Note: without -p i.e. NAME-p = t and no-NAME-p = nil)
 	echo "(setq $(NAME)-p t)" > options/$(NAME).el
 	echo "(setq $(NAME)-p nil)" > options/no-$(NAME).el

readme.org

@@ -155,9 +155,31 @@ This isn't intended to cover everything. This could be considered a template for
 how you could setup your files in a similar way. Look at this org mode file for
 details.
 
-NOTE: Removal of files is YOUR job, not this tools. One could theoretically look
-at what changed between two generations and remove that way. BUT that sounds
-janky and error prone. Removal of files is the users job, not this setup.
+** Removal of files between generations
+
+Removal of files is ultimately *YOUR* job. However... to make it possible to
+remove things if desired a bit easier you can run this makefile target with the
+*OLD* and *NEW* variables set:
+
+#+BEGIN_SRC sh :tangle no
+make removed OLD=generation NEW=generation
+#+END_SRC
+
+This will list all the files/directories recursively not in *OLD* compared to *NEW*.
+
+Example:
+
+#+BEGIN_SRC sh :tangle no
+$ make removed OLD=40 NEW=470
+.Xdefaults
+.Xresources
+.ghc.hs
+escp
+essh
+flushdns
+tomod
+towip
+#+END_SRC
 
 ** Explanation of what is happening