1# $NetBSD: hanoi-include.mk,v 1.3 2022/05/08 07:27:50 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.if $N == 1 25. for from to in ${FROM} ${TO} 26all:: 27 @echo "Move the upper disk from stack ${from} to stack ${to}." 28. endfor 29.else 30_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 31. include "${.PARSEDIR}/${.PARSEFILE}" 32_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 33 34. for from to in ${FROM} ${TO} 35all:: 36 @echo "Move the upper disk from stack ${from} to stack ${to}." 37. endfor 38 39_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 40. include "${.PARSEDIR}/${.PARSEFILE}" 41_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 42.endif 43