1# $NetBSD: hanoi-include.mk,v 1.1 2020/10/03 17:30:54 rillig Exp $ 2# 3# Implements the Towers of Hanoi puzzle, thereby demonstrating a bunch of 4# useful programming techniques: 5# 6# * default assignment using the ?= assignment operator 7# * including the same file recursively 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 -f hanoi-include.mk 15# endless loop: 16# make -f hanoi-include.mk N=3 17 18N?= 5 # Move this number of disks ... 19FROM?= A # ... from this stack ... 20VIA?= B # ... via this stack ... 21TO?= C # ... to this stack. 22 23.if $N == 1 24. for from to in ${FROM} ${TO} 25all:: 26 @echo "Move the upper disk from stack ${from} to stack ${to}." 27. endfor 28.else 29_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 30. include "${.PARSEDIR}/${.PARSEFILE}" 31_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}} 32 33. for from to in ${FROM} ${TO} 34all:: 35 @echo "Move the upper disk from stack ${from} to stack ${to}." 36. endfor 37 38_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 39. include "${.PARSEDIR}/${.PARSEFILE}" 40_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}} 41.endif 42