Re: The state of functional programming

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

Warren wrote:
> Dmitry A. Kazakov expounded in
> news:a3iznu9uq49d$.1m9cupr81yhut$.dlg@40tude.net: 
> 
>> On Thu, 29 Jul 2010 15:20:48 +0000 (UTC), Warren wrote:
> ..
>>> I think you missed my point - perhaps it wasn't expressed
>>> clearly.
>>>
>>> As I understand it, a FP tries to determine conclusions 
>>> from a universe of facts, given some inputs. For smaller
>>> problems this can be _exhaustively_ analyzed and results 
>>> obtained.
>> And so does any declarative language. You declare some facts in
>> whatever form (as relations, as connections of blocks etc, for that
>> matter, as types in a strongly typed languages like Ada). The system
>> infers from them some executable code.
> 
> No, there is a big difference here.
> 
> In a non-FP language (Ada), you can solve _any_ problem so long
> as you code it (you are coding the "how").  IOW, you have
> solved the problem and specified it in code.
> 
> In FP, you define the "problem" (instead) and require from 
> it a solution. But FP cannot always solve that "problem".

Warren, I think your description or understanding of FP matches "logic 
programming" or "constraint programming" rather than "functional 
programming".

FP programs do specify "how" to compute a solution, although the FP 
compiler or interpreter may have to transform the "how" in smart ways to 
make it computable on resource-limited machines -- for example, by 
converting tail recursion to iteration, or by using lazy evaluation to 
avoid infinitely large intermediate results. Proving termination of 
functional programs is similar to proving termination of recursive 
imperative programs.

It is in logic programming and constraint programming that the 
programmer enters facts, rules, and a goal, and the program searches for 
solutions (proofs or realisations of the goal) in some way that is not 
explicitly encoded in the program.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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