Stream programming

Kiuhnm kiuhnm03.4t.yahoo.it
Fri Mar 23 17:02:43 CET 2012


On 3/23/2012 17:00, Kiuhnm wrote:
> I've been writing a little library for handling streams as an excuse for
> doing a little OOP with Python.
>
> I don't share some of the views on readability expressed on this ng.
> Indeed, I believe that a piece of code may very well start as complete
> gibberish and become a pleasure to read after some additional
> information is provided.
>
> I must say that imposed indentation is a pain when one is trying to
> define some sort of DSL (domain specific language). Also, Python's
> operator overloading is a bit limited, but that makes for a more
> rewarding experience in my case.
>
> Here's an example of what you can write:
>
> numbers - push - avrg - 'med' - pop - filter(lt('med'), ge('med'))\
> - ['same', 'same'] - streams(cat) - 'same'
>
> Ok, we're at the "complete gibberish" phase.
>
> Time to give you the "additional information".
>
> I will use "<=>" to mean "is equivalent to". That's not part of the DSL.
> A flow has one or more streams:
> 1 stream:
> [1,2,3]
> 2 streams:
> [1,3,5] | [2,4,6]
> Two flows can be concatenated:
> [1,2,3] + [4,5,6] <=> [1,2,3,4,5,6]
> [0] + ([1,2] | [3,4]) + [10] <=> [0,1,2,10] | [0,3,4,10]
> ([1,2] | [10,20]) + ([3,4] | [30,40]) <=> [1,2,3,4] | [10,20,30,40]
> A flow can be transformed:
> [1,2] - f <=> [f(1),f(2)]
> ([1,2] | [3,4]) - f <=> [f(1,3),f(2,4)]
> ([1,2] | [3,4]) - [f] <=> [f(1),f(2)] | [f(3),f(4)]
> ([1,2] | [3,4]) - [f,g] <=> [f(1),f(2)] | [g(3),g(4)]
> [1,2] - [f,g] <=> [f(1),f(2)] | [g(1),g(2)]
> Some functions are special and almost any function can be made special:
> [1,2,3,4,5] - filter(isprime) <=> [2,3,5]
> [[],(1,2),[3,4,5]] - flatten <=> [1,2,3,4,5]
> Note that 'filter' is not really necessary, thanks to 'flatten'.
> Flows can be named, remembered and used
> as a value:
> [1,2,3,4,5] - 'flow' + val('flow') <=> [1,2,3,4,5]*2
> as a transformation chain:
> [1,2,3] - skipfirst - 'again' | [4,5,6] - func('again')
> <=> [2,3] | [5,6]
> Recursion is also possible and stops when a function is applied to an
> empty sequence.
> Flows can be saved (push) and restored (pop) :
> [1,2,3,4] - push - by(2) - 'double' - pop | val('double')
> <=> [1,2,3,4] | [2,4,6,8]
> There are easier ways to achieve the same result, of course:
> [1,2,3,4] - [id, by(2)]
>
> Let's go back to our example. I didn't tell you anything but you should

Ops... *everything*.

Kiuhnm



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