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make(1): add test demonstrating the Towers of Hanoi puzzle 

It's not the primary task of make to handle procedure calls with
parameters, combined with lexical scoping, therefore the code does not
look as straight-forward or clean as in other programming languages.  It
feels more like squeezing a programming problem from the imperative
world into the world of declarative dependencies.

A more idiomatic way of implementing this puzzle should be as a
dependency graph since that's both the natural structure of the puzzle
and the primary domain of make.  Something like having a main target
"hanoi-5" that depends on intermediate targets of the form
"move-1.2.3.4.5-_._._._._-_._._._._", each representing a single
configuration of the stacks.  These targets could be generated
dynamically.  A benefit of this implementation would be that the puzzle
could be resumed from an arbitrary configuration, just just from the
initial configuration.
This commit is contained in:
rillig 2020-10-03 17:30:54 +00:00
parent 27ec5f2921
commit 6f58a78513
3 changed files with 75 additions and 1 deletions
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3
usr.bin/make/unit-tests/Makefile
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@ -1,4 +1,4 @@
# $NetBSD: Makefile,v 1.158 2020/10/03 14:39:36 rillig Exp $
# $NetBSD: Makefile,v 1.159 2020/10/03 17:30:54 rillig Exp $
#
# Unit tests for make(1)
#
@ -168,6 +168,7 @@ TESTS+= export-env
TESTS+= export-variants
TESTS+= forloop
TESTS+= forsubst
TESTS+= hanoi-include
TESTS+= impsrc
TESTS+= include-main
TESTS+= job-output-long-lines

32
usr.bin/make/unit-tests/hanoi-include.exp Normal file
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@ -0,0 +1,32 @@
Move the upper disk from stack A to stack C.
Move the upper disk from stack A to stack B.
Move the upper disk from stack C to stack B.
Move the upper disk from stack A to stack C.
Move the upper disk from stack B to stack A.
Move the upper disk from stack B to stack C.
Move the upper disk from stack A to stack C.
Move the upper disk from stack A to stack B.
Move the upper disk from stack C to stack B.
Move the upper disk from stack C to stack A.
Move the upper disk from stack B to stack A.
Move the upper disk from stack C to stack B.
Move the upper disk from stack A to stack C.
Move the upper disk from stack A to stack B.
Move the upper disk from stack C to stack B.
Move the upper disk from stack A to stack C.
Move the upper disk from stack B to stack A.
Move the upper disk from stack B to stack C.
Move the upper disk from stack A to stack C.
Move the upper disk from stack B to stack A.
Move the upper disk from stack C to stack B.
Move the upper disk from stack C to stack A.
Move the upper disk from stack B to stack A.
Move the upper disk from stack B to stack C.
Move the upper disk from stack A to stack C.
Move the upper disk from stack A to stack B.
Move the upper disk from stack C to stack B.
Move the upper disk from stack A to stack C.
Move the upper disk from stack B to stack A.
Move the upper disk from stack B to stack C.
Move the upper disk from stack A to stack C.
exit status 0

41
usr.bin/make/unit-tests/hanoi-include.mk Normal file
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@ -0,0 +1,41 @@
# $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