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# $NetBSD: hanoi-include.mk,v 1.1 2020/10/03 17:30:54 rillig Exp $
#
# Implements the Towers of Hanoi puzzle, thereby demonstrating a bunch of
# useful programming techniques:
#
# * default assignment using the ?= assignment operator
# * including the same file recursively
# * extracting the current value of a variable using the .for loop
# * using shell commands for calculations since make is a text processor
# * using the :: dependency operator for adding commands to a target
# * on-the-fly variable assignment expressions using the ::= modifier
#
# usage:
# env N=3 make -f hanoi-include.mk
# endless loop:
# make -f hanoi-include.mk N=3
N?= 5 # Move this number of disks ...
FROM?= A # ... from this stack ...
VIA?= B # ... via this stack ...
TO?= C # ... to this stack.
.if $N == 1
. for from to in ${FROM} ${TO}
all::
@echo "Move the upper disk from stack ${from} to stack ${to}."
. endfor
.else
_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
. include "${.PARSEDIR}/${.PARSEFILE}"
_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
. for from to in ${FROM} ${TO}
all::
@echo "Move the upper disk from stack ${from} to stack ${to}."
. endfor
_:= ${N::!=expr $N - 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
. include "${.PARSEDIR}/${.PARSEFILE}"
_:= ${N::!=expr $N + 1} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
.endif
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