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 20N?= 5 # Move this number of disks ... 21FROM?= A # ... from this stack ... 22VIA?= B # ... via this stack ... 23TO?= 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 28N:= count ${:U:${:Urange=$N}} # 'count' + one word for every disk 29.endif 30 31.if ${N:[#]} == 2 32. for from to in ${FROM} ${TO} 33all:: 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} 42all:: 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