hanoi-include.mk revision 1.4
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 19 N?= 5 # Move this number of disks ... 20 FROM?= A # ... from this stack ... 21 VIA?= B # ... via this stack ... 22 TO?= 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 27 N:= count ${:U:${:Urange=$N}} # 'count' + one word for every disk 28 .endif 29 30 .if ${N:[#]} == 2 31 . for from to in ${FROM} ${TO} 32 all:: 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} 41 all:: 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
Indexes created Mon Sep 29 21:09:56 GMT 2025