49 lines
1.7 KiB
Makefile
49 lines
1.7 KiB
Makefile
# $NetBSD: hanoi-include.mk,v 1.4 2023/01/19 22:48:42 rillig Exp $
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#
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# Implements the Towers of Hanoi puzzle, demonstrating a bunch of more or less
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# useful programming techniques:
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#
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# * default assignment using the ?= assignment operator
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# * including the same file recursively (rather unusual)
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# * extracting the current value of a variable using the .for loop
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# * using shell commands for calculations since make is a text processor
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# * using the :: dependency operator for adding commands to a target
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# * on-the-fly variable assignment expressions using the ::= modifier
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#
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# usage:
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# env N=3 make -r -f hanoi-include.mk
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#
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# endless loop, since command line variables cannot be overridden:
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# make -r -f hanoi-include.mk N=3
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N?= 5 # Move this number of disks ...
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FROM?= A # ... from this stack ...
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VIA?= B # ... via this stack ...
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TO?= C # ... to this stack.
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# Since make has no built-in arithmetic functions, convert N to a list of
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# words and use the built-in word counting instead.
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.if ${N:[#]} == 1
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N:= count ${:U:${:Urange=$N}} # 'count' + one word for every disk
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.endif
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.if ${N:[#]} == 2
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. for from to in ${FROM} ${TO}
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all::
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@echo "Move the upper disk from stack ${from} to stack ${to}."
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. endfor
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.else
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_:= ${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
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. include "${.PARSEDIR}/${.PARSEFILE}"
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_:= ${N::+=D} ${TMP::=${VIA}} ${VIA::=${TO}} ${TO::=${TMP}}
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. for from to in ${FROM} ${TO}
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all::
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@echo "Move the upper disk from stack ${from} to stack ${to}."
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. endfor
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_:= ${N::=${N:[1..-2]}} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
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. include "${.PARSEDIR}/${.PARSEFILE}"
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_:= ${N::+=D} ${TMP::=${VIA}} ${VIA::=${FROM}} ${FROM::=${TMP}}
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.endif
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