1# $NetBSD: hanoi-include.mk,v 1.4 2023/01/19 22:48:42 rillig Exp $
2#
3# Implements the Towers of Hanoi puzzle, demonstrating a bunch of more or less
4# useful programming techniques:
5#
6#	* default assignment using the ?= assignment operator
7#	* including the same file recursively (rather unusual)
8#	* extracting the current value of a variable using the .for loop
9#	* using shell commands for calculations since make is a text processor
10#	* using the :: dependency operator for adding commands to a target
11#	* on-the-fly variable assignment expressions using the ::= modifier
12#
13# usage:
14#	env N=3 make -r -f hanoi-include.mk
15#
16# endless loop, since command line variables cannot be overridden:
17#	make -r -f hanoi-include.mk N=3
18
19N?=	5			# Move this number of disks ...
20FROM?=	A			# ... from this stack ...
21VIA?=	B			# ... via this stack ...
22TO?=	C			# ... to this stack.
23
24# Since make has no built-in arithmetic functions, convert N to a list of
25# words and use the built-in word counting instead.
26.if ${N:[#]} == 1
27N:=	count ${:U:${:Urange=$N}}	# 'count' + one word for every disk
28.endif
29
30.if ${N:[#]} == 2
31.  for from to in ${FROM} ${TO}
32all::
33	@echo "Move the upper disk from stack ${from} to stack ${to}."
34.  endfor
35.else
36_:=	${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
37.  include "${.PARSEDIR}/${.PARSEFILE}"
38_:=	${N::+=D} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
39
40.  for from to in ${FROM} ${TO}
41all::
42	@echo "Move the upper disk from stack ${from} to stack ${to}."
43.  endfor
44
45_:=	${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
46.  include "${.PARSEDIR}/${.PARSEFILE}"
47_:=	${N::+=D} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
48.endif
49