Rich Hickey's slides from jvm lang summit - worth a read?

[Rich Hickey]

bearophile Wrote:

> Walter Bright:
> 
> > Executive summary: pure functions and immutable data structures help 
> > manage program complexity.
> 
> There's something missing in most of the articles I've read that praise pure functions and immutable data structures. When I write a 500-lines long Python program I often start using almost pure data structures and pure functions, they help me avoid bugs and keep things tidy. Then if the performance is good enough I may stop (I add more tests, docs, etc).
> 
> If the performance isn't good enough I often profile the code and (beside trying to improve algorithms and data structures, catching and pre-processing, etc), I also sometimes reduce the purity of some performance critical functions/methods and change the code in some spots so it modifies some big data structures in place, to avoid repeated allocations and reduce GC activity. This speeds up the code.
> 
> I'd like a language that helps me perform such changes from almost purity to a code that in certain spots is less functional/pure. I'd like such language to give me quick ways to go back to a more pure code, to help me modify/debug the code further, because during program design or during debugging purity/immutability help. But once I have optimized my Python code, I have lost some of such simplicity, and it requires work if you want to go back to a more pure code to perform more debugging/code improvements. I think such ideas may be applied to D programs too.
> 

You might find this interesting:

http://clojure.org/transients

It supports using the exact same immutable data structures in/out of your (externally pure) function, as well as the exact same functional "shape" of your code when using transients (roughly, mutables) internally.

Rich