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hanoi-include.mk revision 1.3 
      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 
     19 N?=	5			# Move this number of disks ...
     20 FROM?=	A			# ... from this stack ...
     21 VIA?=	B			# ... via this stack ...
     22 TO?=	C			# ... to this stack.
     23 
     24 .if $N == 1
     25 .  for from to in ${FROM} ${TO}
     26 all::
     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}
     35 all::
     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