[Chicken-janitors] Re: #416: Make stock errors more usable programmatically

[Chicken Trac]

#416: Make stock errors more usable programmatically
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  Reporter:  syn             |       Owner:        
      Type:  enhancement     |      Status:  closed
  Priority:  minor           |   Milestone:  4.7.0 
 Component:  core libraries  |     Version:  4.6.x 
Resolution:  wontfix         |    Keywords:        
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Comment(by syn):

 Replying to [comment:8 felix]:
 > This just leads to programming by accident. Try to avoid errors instead
 of using exception-handling as a substitution for control-flow.

 Well, I think it's a question of how anal one is about certain kinds of
 problems. Say you have a program that can either load some cached state
 from a file if it exists or otherwise calculate it live. AFAIU your
 suggestion, one should do something like {{{ (when (file-exists? "cache")
 (set! state (with-input-from-file "cache" read-state))) }}} and I would
 generally agree, mostly for stylistic reasons. However we now have
 introduced a race condition into our program: Should the file disappear
 between checking for its existence and reading it, it will fail although
 it could perfectly continue without loading the file. This means we would
 probably want to catch ENOENT errors but still fail on others (thus my
 initial request for more specific errors). If we do that though we don't
 really need the {{{file-exists?}}}  call anymore, it is actually redundant
 with catching the error. Granted, this is a contrived example but I think
 it is an example of a more general class of problems. Feel free to
 disagree, of course, I'm not entirely committed to this either :-)

-- 
Ticket URL: <http://bugs.call-cc.org/ticket/416#comment:9>
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