The Man or Boy Recursion Test
Werner
being new to ruby I try to understand the language. In a different
context I came across the following:
http://en.wikipedia.org/wiki/Man_or_boy_test
Out of curiosity I tried to write an equivalent piece of code in ruby
but apparently my depth of knowledge is not good enough.
Is there anyone who could enlighten me?
Thanks and Best Regards
Werner Dahn
Tim Hunter
# Man or boy test
def a(k, x1, x2, x3, x4, x5)
b ||= Proc.new { k -= 1; a(k, b, x1, x2, x3, x4) }
return k <= 0 ? x4[] + x5[] : b[]
end
puts a(10, Proc.new {1}, Proc.new {-1}, Proc.new {-1}, Proc.new {1},
Proc.new {0})
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Lloyd Linklater
> Werner wrote:
>> Is there anyone who could enlighten me?
>>
>> Thanks and Best Regards
>>
>> Werner Dahn
>>
>
> # Man or boy test
> def a(k, x1, x2, x3, x4, x5)
> b ||= Proc.new { k -= 1; a(k, b, x1, x2, x3, x4) }
> return k <= 0 ? x4[] + x5[] : b[]
> end
>
> puts a(10, Proc.new {1}, Proc.new {-1}, Proc.new {-1}, Proc.new {1},
> Proc.new {0})
Nice post, Tim. I tested it and, when it gave the correct answer, I
decided to share it with the world.
http://en.wikipedia.org/wiki/Man_or_boy_test
--
Posted via http://www.ruby-forum.com/.
Werner
> def a(k, x1, x2, x3, x4, x5)
> b ||= Proc.new { k -= 1; a(k, b, x1, x2, x3, x4) }
> return k <= 0 ? x4[] + x5[] : b[]
> end
>
> puts a(10, Proc.new {1}, Proc.new {-1}, Proc.new {-1}, Proc.new {1},
> Proc.new {0})
>
Best Regards
Werner Dahn
Tim Hunter
Sweet!
I realized last night that the ||= is superfluous. A simple assignment
is enough.
b = Proc.new { k -= 1; a(k, b, x1, x2, x3, x4) }
Rick DeNatale
>
> I realized last night that the ||= is superfluous. A simple assignment
> is enough.
>
> b = Proc.new { k -= 1; a(k, b, x1, x2, x3, x4) }
Right, because b will always be nil here, it's a local variable so
there's a new b for each resursion. Otherwise it would kind of defeat
what the Man Or Boy example is trying to illustrate.
And it can be made a little shorter, and more computer sciency <G>, by
replacing all those "Proc.new"s with "lambda"s.
# Man or boy test
def a(k, x1, x2, x3, x4, x5)
b = lambda { k -= 1; a(k, b, x1, x2, x3, x4) }
return k <= 0 ? x4[] + x5[] : b[]
end
puts a(10, lambda {1}, lambda {-1}, lambda {-1}, lambda {1}, lambda {0})
--
Rick DeNatale
My blog on Ruby
http://talklikeaduck.denhaven2.com/
Lloyd Linklater
haskell, smalltalk. I sense that a snowball has started an avalanche!
:)
Tim Hunter
> Since I posted your ruby version, there have been more posts in C,
> haskell, smalltalk. I sense that a snowball has started an avalanche!
> :)
Well, the Ruby version certainly wins the Man-or-boy-test-golf contest.
But I've been programming in C for over 20 years and I can say with
authority that whoever did the C version has C-coding cojones the size
of hubcaps.
Morton Goldberg
Surely we can eliminate the 'return' too and make it even shorter:
def a(k, x1, x2, x3, x4, x5)
b = lambda { k -= 1; a(k, b, x1, x2, x3, x4) }
k <= 0 ? x4[] + x5[] : b[]
end
puts a(10, lambda {1}, lambda {-1}, lambda {-1}, lambda {1}, lambda {0})
Regards, Morton
Rick DeNatale
> Well, the Ruby version certainly wins the Man-or-boy-test-golf contest.
> But I've been programming in C for over 20 years and I can say with
> authority that whoever did the C version has C-coding cojones the size
> of hubcaps.
I was surprised and amused to find that there was already an PL/I
implementation in the wikipedia article.
A much (unnecessarily) maligned language deep in my past.
Tim Hunter
> On Nov 11, 2007 3:18 PM, Tim Hunter <TimH...@nc.rr.com> wrote:
>
>> Well, the Ruby version certainly wins the Man-or-boy-test-golf contest.
>> But I've been programming in C for over 20 years and I can say with
>> authority that whoever did the C version has C-coding cojones the size
>> of hubcaps.
>
> I was surprised and amused to find that there was already an PL/I
> implementation in the wikipedia article.
>
> A much (unnecessarily) maligned language deep in my past.
>
Ummmm...before I wrote C I wrote PL/I. Not a lot, but enough to be able
to use the PL/I version of the Man or Boy test to figure out how to code
the Ruby version.
Rick DeNatale
> Rick DeNatale wrote:
> > On Nov 11, 2007 3:18 PM, Tim Hunter <TimH...@nc.rr.com> wrote:
> >
> >> Well, the Ruby version certainly wins the Man-or-boy-test-golf contest.
> >> But I've been programming in C for over 20 years and I can say with
> >> authority that whoever did the C version has C-coding cojones the size
> >> of hubcaps.
> >
> > I was surprised and amused to find that there was already an PL/I
> > implementation in the wikipedia article.
> >
> > A much (unnecessarily) maligned language deep in my past.
> >
>
> Ummmm...before I wrote C I wrote PL/I. Not a lot, but enough to be able
> to use the PL/I version of the Man or Boy test to figure out how to code
> the Ruby version.
Sometimes I feel my age.
Last week I gave a talk to the local "agile" meetup group about "A
History of Agility" When I introduced myself I said that I started
programming in College in 1970. Out of the 15-20 people in the
audience, only about 3-4 were born then, some by only a few months.
Morton Goldberg
> Ummmm...before I wrote C I wrote PL/I. Not a lot, but enough to be
> able to use the PL/I version of the Man or Boy test to figure out
> how to code the Ruby version.
Interesting. I used your Ruby version to figure out how to code it in
Mathematica. I was able to make a fairly direct translation.
<code>
$RecursionLimit = 1665; (* anything less fails for k0 = 10 *)
a[k0_, x1_, x2_, x3_, x4_, x5_] := Module[{k, b },
k = k0;
b = (k--; a[k, b, x1, x2, x3, x4]) &;
If[k <= 0, x4[] + x5[], b[]]]
a[10, 1 &, -1 &, -1 &, 1 &, 0 &] (* => -67 *)
</code>
Note how compact the Mathematica notation for the thunks is.
Regards, Morton
Tim Hunter
Another one for Wikipedia. I guess we owe Werner (the OP) a big "thanks"
for introducing such an interesting thread. Thanks, Werner!
Lloyd Linklater
Your post did not have the formatting that the other languages did. I
added that for you so the other kids would not make fun of your code.
:) I did not use any language coloring as the wiki does not recognize
mathmatica.
I hope that you do not mind.
Morton Goldberg
> Morton Goldberg wrote:
>> On Nov 11, 2007, at 6:42 PM, Tim Hunter wrote:
>>> Ummmm...before I wrote C I wrote PL/I. Not a lot, but enough to
>>> be able to use the PL/I version of the Man or Boy test to figure
>>> out how to code the Ruby version.
>> Interesting. I used your Ruby version to figure out how to code it
>> in Mathematica. I was able to make a fairly direct translation.
>> <code>
>> $RecursionLimit = 1665; (* anything less fails for k0 = 10 *)
>> a[k0_, x1_, x2_, x3_, x4_, x5_] := Module[{k, b },
>> k = k0;
>> b = (k--; a[k, b, x1, x2, x3, x4]) &;
>> If[k <= 0, x4[] + x5[], b[]]]
>> a[10, 1 &, -1 &, -1 &, 1 &, 0 &] (* => -67 *)
>> </code>
>> Note how compact the Mathematica notation for the thunks is.
>> Regards, Morton
>
> Another one for Wikipedia.
I've posted it there. I like the Smalltalk example also -- very
concise yet still readable.
> I guess we owe Werner (the OP) a big "thanks" for introducing such
> an interesting thread. Thanks, Werner!
Indeed.
Regards, Morton
Morton Goldberg
> Morton,
>
> Your post did not have the formatting that the other languages
> did. I
> added that for you so the other kids would not make fun of your code.
> :) I did not use any language coloring as the wiki does not recognize
> mathmatica.
I'm glad you fixed it up. That was my first post on Wikipedia. I
tried <source lang="mathematica">, but as you pointed out, that
doesn't work. I didn't know that <source lang="text"> was the best
alternative. But I do now :). Thanks.
Regards, Morton