Re: [Caml-list] OCaml and Design Patterns

[Brian Hurt <bhurt@spnz.org>]

On Wed, 20 Oct 2004, David Brown wrote:

> On Wed, Oct 20, 2004 at 06:30:01PM +0100, Richard Jones wrote:
> 
> > Just my personal opinion, but I've seen a lot of terrible code written
> > which uses "design patterns" ...  A lot of the patterns seem to exist
> > solely to bypass problems with OO languages.
> 
> Design Patterns seem very similar to what is usually called idioms in other
> languages.  They're just common constructs you learn for common tasks.  An
> example in ocaml might be typical recursion for a loop.
> 
> However, the OO Design Patterns do seem more to be techniques used to
> compensate for defects in the OO methodology, or specific languages.
> 
> I would suspect that when someone encounters a place to use a design
> pattern in OCaml, the problem would much better be solved by using some
> other feature of the language.
> 

I don't seem to have quite as negative a view of the GoF book as many 
people around here seem to.  But I think this is because I see design 
patterns as a more general idea than just what the GoF presented- and I'd 
argue this view is supported by the pattern community- as now you have 
software architecture patterns, anti-patterns, etc.  I think there are OO 
patterns (which is what is documented in the GoF book), functional 
patterns, even procedural patterns.

I also think that the difference between idioms and patterns is mainly a
matter of degree- they're all of a kind, if you see.

Note that there are a number of Functional patterns which are for working 
around the limitations of the Ocaml language as well.  An example I'll 
hold up here is "build a list backwards, then reverse it" pattern, to make 
a function tail recursive.  Others are less clear cut- is "return the 
update applicative structure" a work-around, or a better way of doing 
things?

The point I'd like to make to the original poster is that the GoF isn't 
the last word on how to think about problems, especially not in Ocaml.  
Look for the new patterns Ocaml allows/encourages.

-- 
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                                - Gene Spafford 
Brian

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