Here is a new program. Perhaps you would consider this declarative:
def valid(a,b,c,d):
weights = set(w*a+x*b+y*c+z*d for (w,x,y,z) in
product([-1,0,1],repeat=4))
return weights >= set(range(1,41))
ws = [(a,b,c,d) for (a,b,c,d) in product(range(1,41),repeat=4)
if a <= b <= c <= d and a+b+c+d == 40 and
valid(a,b,c,d)]
On 12 nov, 01:48, Jules <julesjac...@gmail.com> wrote:
> Are we reading the same cKanren code? I'll give you that the matches
> definition is declarative, but then read checko and subchecko. They
> are all about (recursive) control flow. Where does the specification
> say anything remotely close to the checko and subchecko relations? In
> contrast to this, the Python set comprehensions have minimal control
> flow. Yeah, the standard Python implementation has a certain order of
> executing the comprehensions, but so does the cKanren implementation
> when executing the predicates. My Python program doesn't depend on
> this order: it just uses declarative descriptions of sets as set
> comprehensions.
>
> Just being written in cKanren doesn't make a program declarative. If
> you write a C interpreter in cKanren and then write your actual
> program in a literal string, that doesn't magically make the program
> declarative even though it is a cKanren program. Similarly, checko and
> subchecko don't describe the problem in a declarative way. Compare
> this with the Python valid() function: the set of possible weights you
> can make has to be a superset of {1..40}. Again, declarativeness is a
> property of programs, not languages. Some languages make writing
> declarative programs easier, of course. cKanren is supposed to be such
> a language, so it would be neat to see a more declarative cKanren
> program for this problem.
>
> Also, I don't see how "one stone should weigh 1lbs" is part of the
> specification. Now, it is true that the answer happens to have one
> stone equal to 1, but how is that part of or trivially follows from
> the specification? We might as well hard-code the whole solution.
>
> Jules
>
> On 12 nov, 00:49, Timothy Baldridge <tbaldri...@gmail.com> wrote:
>
>
>
>
>
>
>
> > > My Python code is much more declarative than the given
> > > cKanren code in that regard. Just
> > > compare:http://dosync.posterous.com/another-taste-of-ckanren
>
> > I don't think you understand what declarative programming is at its
> > core. Declarative programming
>
> > To borrow from the ever-present wikipedia:
> > "declarative programming is a programming paradigm that expresses the
> > logic of a computation without describing its control flow.[1] Many
> > languages applying this style attempt to minimize or eliminate side
> > effects by describing what the program should accomplish, rather than
> > describing how to go about accomplishing it.[2] This is in contrast
> > with imperative programming, which requires an explicitly provided
> > algorithm." (see: Declarative Programming)
>
> > This is where the cKanren code succeeds where the Python code fails.
> > The Python code is all algorithm, and no facts. While the cKanren code
> > is a direct implementation of the facts about the problem: one stone
> > must be 1lb all stones should equal 40lb, etc. The cKanren code leaves
> > the interpretation of these facts up to the logic engine, while the
> > Python code sets strict guidelines that the compiler must follow. If,
> > for instance, it was faster for a given computer to count down from
> > instead of counting up, the Python code would run much slower, by
> > defining the algorithm (by using range, and for loops), you're
> > restricting the interpreter to your view of how to solve the problem.
> > The cKanren compiler/interpreter/whatever is free to solve the problem
> > in any way it pleases, as long as the requirements (facts) are met.
> > The original problem states "find 4 numbers that equal 40 but a
> > combination of any of which can be 1 through 40" it says nothing of
> > range sequences, for loops, etc.
>
> > Timothy
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