Re: Continuations

[Matthias Felleisen <address@hidden>]

Anton, you have hit the nail on the head. If these articles could just 
reach
the implementors of the dozen or so LLs, that would be really great.

-- Matthias

On Saturday, August 9, 2003, at 05:13 PM, Anton van Straaten wrote:

> Dan Sugalski wrote:
>> At 4:12 PM -0400 8/8/03, Alan Bawden wrote:
>>> Don't Perl or Java programmers ever write interpreters?
>>
>> Rarely. These days almost *nobody* writes interpreters.
>
> I agree, based on what I've seen.
>
>> But, then almost nobody ever has. In the past there were just fewer
>> people overall, so almost nobody was a larger percentage of the
>> population.
>
> That doesn't address why so few people write interpreters.  I'll 
> speculate:
>
> 1.  Most programmers don't know why they should want to write an
> interpreter.
> 2.  Most programmers think writing an interpreter must be very 
> difficult.
> 3.  Many mainstream languages don't make it easy to write interpreters.
> 4.  By (3), most programmers are correct about (2).
> 5.  Mainstream languages that do make it easier to write interpreters 
> tend
> to be languages like Perl or Python, which are already interpreters.  
> An
> interpreter implemented in an interpreted language is correctly 
> perceived as
> being likely to be very slow, and thus seems like a dead end to most
> programmers, who by (1), don't know that it might make sense to write 
> an
> interpreter just as a learning experience.
>
> I think it can reasonably be argued that the "average" programmer 
> does, in
> fact, have little reason to want write an interpreter.  But the same 
> isn't
> true for an "above average" programmer.  I'd argue that too few
> above-average programmers write interpreters, because of the above 
> factors,
> but also because of this one:
>
> 6.  Most programmers have very little by way of accessible resources to
> teach them how to write an interpreter.  For most programmers, books 
> like
> SICP, HtDP and EoPL are not accessible resources.  Even though an above
> average programmer might be capable of understanding them, they tend 
> to be
> too far removed from what those programmers are familiar with, and 
> require
> too much commitment for an uncertain payoff - speaking from the 
> perspective
> of the programmer who doesn't quite know what he's going to get out of
> learning a foreign programming language and slogging through books 
> written
> in a foreign semi-formal language.  This is not a critique of those 
> books,
> it's just that they don't necessarily extend all that far beyond the 
> target
> audience for which they're designed, i.e. students at academic 
> institutions.
>
> More accessible resources include some of the sorts of books and 
> magazines
> you find in retail bookstores, and articles on popular developer's web
> sites.  I suspect a series of articles about how to implement 
> interpreters
> in mainstream languages could spark some interest and spread some 
> useful
> knowledge, *but* the articles would have to do a good job of 
> motivating the
> activity with applications that go beyond learning about e.g. 
> continuations.
>
> It's possible that above-average programmers might be appealed to by 
> the
> sheer joy of learning and the prospect of gaining knowledge that could 
> be
> indirectly useful, but I suspect if that were the only motivation, it 
> would
> seriously restrict the audience.  Explaining that implementing 
> interpreters
> allows one to implement domain-specific languages is unlikely to help 
> much,
> because most programmers don't think explicitly in terms of solving 
> problems
> by implementing DSLs, and so that whole concept would first need to be
> motivated.
>
> I'm rambling like this because I think it's a pity that this sort of
> knowledge isn't a little more widespread.  I think the status quo 
> reflects
> the fact that above-average programmers who have not been exposed to 
> modern
> academic computing science, are unnecessarily constrained by the "Teach
> yourself Java in 21 days" atmosphere of the mainstream programming 
> world.
> There's very little by way of bridges between that world and the world 
> to
> which SICP is one of the doorways.  (This list being a welcome 
> exception, of
> course!)
>
> Anton