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hanoi-include.mk revision 1.1 
      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 
     18 N?=	5			# Move this number of disks ...
     19 FROM?=	A			# ... from this stack ...
     20 VIA?=	B			# ... via this stack ...
     21 TO?=	C			# ... to this stack.
     22 
     23 .if $N == 1
     24 .  for from to in ${FROM} ${TO}
     25 all::
     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}
     34 all::
     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