hanoi-include.mk revision 1.5
1 # $NetBSD: hanoi-include.mk,v 1.5 2023/10/19 18:24:33 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 the :: dependency operator for adding commands to a target 10 # * on-the-fly variable assignment expressions using the ::= modifier 11 # 12 # usage: 13 # env N=3 make -r -f hanoi-include.mk 14 # 15 # Specifying N in the command line instead of in the environment would produce 16 # an endless loop, since variables from the command line cannot be overridden 17 # by global variables: 18 # make -r -f hanoi-include.mk N=3 19 20 N?= 5 # Move this number of disks ... 21 FROM?= A # ... from this stack ... 22 VIA?= B # ... via this stack ... 23 TO?= C # ... to this stack. 24 25 # Since make has no built-in arithmetic functions, convert N to a list of 26 # words and use the built-in word counting instead. 27 .if ${N:[#]} == 1 28 N:= count ${:U:${:Urange=$N}} # 'count' + one word for every disk 29 .endif 30 31 .if ${N:[#]} == 2 32 . for from to in ${FROM} ${TO} 33 all:: 34 @echo "Move the upper disk from stack ${from} to stack ${to}." 35 . endfor 36 .else 37 _:= ${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 38 . include "${.PARSEDIR}/${.PARSEFILE}" 39 _:= ${N::+=D} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 40 41 . for from to in ${FROM} ${TO} 42 all:: 43 @echo "Move the upper disk from stack ${from} to stack ${to}." 44 . endfor 45 46 _:= ${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 47 . include "${.PARSEDIR}/${.PARSEFILE}" 48 _:= ${N::+=D} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 49 .endif 50
Indexes created Mon Sep 29 21:09:56 GMT 2025