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(Ab)Using Language Features: The Common Lisp Condition System

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Re: (Ab)Using Language Features: The Common Lisp Condition System

#21

Post by draegtun »

kbenson wrote: post #8
howeyc wrote: post #4

This was something I really loved during my time in Common Lisp. This was a gem that I was hoping would make it into Clojure, but I think around version 1.3 they decided to abandon the idea and add a library to "make anything throwable" which totally missed the point in my opinion. Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack…

Perl 6 allows for handling exception in a same-scope CATCH block, so you can try to recover. It can probably be mixed with their phasers[1] in interesting ways. Also of interest might be control exceptions[2]. 1: http://perlcabal.org/syn/S04.html#Phasers 2: http://perlcabal.org/syn/S04.html#Control_Exceptions

Here is an interesting perl6 example which works in Rakudo:

  $ perl6

  > $*PERL;
  rakudo

  > $*PERL;
  2014.03.01

  > { CONTROL { print 1; $_.resume }; print 2; warn; say 3 }
  213
ref: https://news.ycombinator.com/item?id=7192294

For a perl5 Condition System see this implementation - https://metacpan.org/pod/ConditionSystem

Re: (Ab)Using Language Features: The Common Lisp Condition System

#22

Post by mst »

draegtun wrote: post #21
kbenson wrote: post #8

Earlier quoted context omitted.

Perl 6 allows for handling exception in a same-scope CATCH block, so you can try to recover. It can probably be mixed with their phasers[1] in interesting ways. Also of interest might be control exceptions[2]. 1: http://perlcabal.org/syn/S04.html#Phasers 2: http://perlcabal.org/syn/S04.html#Control_Exceptions

Here is an interesting perl6 example which works in Rakudo: $ perl6 > $*PERL ; rakudo > $*PERL ; 2014.03.01 > { CONTROL { print 1; $_.resume }; print 2; warn; say 3 } 213 ref: https://news.ycombinator.com/item?id=7192294 For a perl5 Condition System see this implementation - https://metacpan.org/pod/ConditionSystem

That one's still exception based. You wanted

http://p3rl.org/Worlogog::Incident http://p3rl.org/Worlogog::Restart

which uses Return::MultiLevel to do stack unwinds that can pass through try/catch constructs.

Re: (Ab)Using Language Features: The Common Lisp Condition System

#23

Post by aufreak3 »

howeyc wrote: post #4

This was something I really loved during my time in Common Lisp. This was a gem that I was hoping would make it into Clojure, but I think around version 1.3 they decided to abandon the idea and add a library to "make anything throwable" which totally missed the point in my opinion. Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack…

> Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack?

While it isn't a mainstream language by any means, a scheme dialect called muSE [1] that I developed for writing logic for automatic music video construction supports such resumes and retries. [2]

[1] https://code.google.com/p/muvee-symbolic-expressions/

[2] https://code.google.com/p/muvee-symbolic-expressions/wiki/Ex...

(Apologies for shameless plug)

-- edit: I just saw that the clojure library "ribol" has an api design similar to muSE's in principle. A couple of design comments though -

1. The "on blah blah" is too much syntax for this. It prevents direct sharing of handlers between similar situations. Function argument pattern matching ought to be enough.

2. The retry options mechanism is somewhat limited - the options seem to apply only at the raise point itself (disclaimer: I've only had a quick glance at ribol). It is more useful to have multiple retry options at different scopes so you can partially unwind, try something, if that doesn't work unwind some more (perhaps involving cleanup), try something else, etc.

I think muSE's design is better on both these fronts.

Re: (Ab)Using Language Features: The Common Lisp Condition System

#24

Post by BruceM »

howeyc wrote: post #4

This was something I really loved during my time in Common Lisp. This was a gem that I was hoping would make it into Clojure, but I think around version 1.3 they decided to abandon the idea and add a library to "make anything throwable" which totally missed the point in my opinion. Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack…

> Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack?

Dylan (http://opendylan.org/) has them, but that's because some of the same people who standardized Common Lisp went on to design Dylan.

Re: (Ab)Using Language Features: The Common Lisp Condition System

#25

Post by aufreak3 »

howeyc wrote: post #4

This was something I really loved during my time in Common Lisp. This was a gem that I was hoping would make it into Clojure, but I think around version 1.3 they decided to abandon the idea and add a library to "make anything throwable" which totally missed the point in my opinion. Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack…

> Are there any other languages that allow the calling scope to specify how lower-level functions handle errors without unwinding the stack?

another possible answer - Erlang.

While the look of the condition/restart scheme may be very different, such a condition/restart protocol can be implemented as message passing with a known global "condition handler" process I think.

A "raise" function can be implemented as a message-send to the condition handler process followed by an immediate wait-for-response. The handler process may terminate the raising process, replace its value with something, etc. depending on the installed handlers.

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