doall example

2014-05-16 Thread Brian Craft
I came across this today in a library:

results (seq (doall (filter modified? files)))]

I believe the seq is to coerce the empty list to nil. What is the doall for?

Context here:

https://github.com/ibdknox/watchtower/blob/master/src/watchtower/core.clj

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Re: doall example

2014-05-16 Thread James Reeves
The doall evaluates all items in the seq, effectively removing any lazy
evaluation. In this case it's necessary because the filter is checking the
modification date of the file, which is obviously mutable.

- James



On 17 May 2014 00:39, Brian Craft craft.br...@gmail.com wrote:

 I came across this today in a library:

 results (seq (doall (filter modified? files)))]

 I believe the seq is to coerce the empty list to nil. What is the doall
 for?

 Context here:

 https://github.com/ibdknox/watchtower/blob/master/src/watchtower/core.clj

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Re: doall example

2014-05-16 Thread Brian Craft
Ah, thanks. Seems like there's still a race, though. In a long list of 
files, a sequence like

1) doall evaluates modification date of the first file, which is less than 
*last-pass*, so it is filtered out
2) something touches the first file
3) the doall finishes evaluating the rest of the list, after which 
*last-pass* is set to the current time

Now the first file has been updated, but still has modification date less 
than *last-pass*, and will be filtered out of the next pass as well.



On Friday, May 16, 2014 4:50:19 PM UTC-7, James Reeves wrote:

 The doall evaluates all items in the seq, effectively removing any lazy 
 evaluation. In this case it's necessary because the filter is checking the 
 modification date of the file, which is obviously mutable.

 - James



 On 17 May 2014 00:39, Brian Craft craft...@gmail.com javascript:wrote:

 I came across this today in a library:

 results (seq (doall (filter modified? files)))]

 I believe the seq is to coerce the empty list to nil. What is the doall 
 for?

 Context here:

 https://github.com/ibdknox/watchtower/blob/master/src/watchtower/core.clj
  
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