gmane.comp.lang.factor.general

Re: What is a good definition ?

Hi,

Eric nicely gave me his solution :

DEFER: combinations

: (combinations) [ 1 tail ] dip combinations ;

: prefix-each [ prefix ] curry map ;

: combinations ( seq n -- seqs )

  {

  { [ dup 0 = ] [ 2drop { { } } ] }

  { [ over empty? ] [ 2drop { } ] }

  { [ t ] [

  [ [ 1- (combinations) ] [ drop first ] 2bi prefix-each ]

  [ (combinations) ] 2bi append

  ] }

  } cond ;

It looks nice :

- only three conditions,

- very few shuffle words

- a good name

- prefix-each makes sens

OK lets try

[ 20 20 <array> 20 [ among ] with each ] time

=> "end > sequence" error

I missed something (Eric didn't !)

I add a condition to my def that becomes

: columnize ( seq -- seq )

[ 1array ] map

; inline

: among ( seq n -- seqs )

2dup swap length

{

{ [ over 1 = ] [ 3drop columnize ] }

{ [ over 0 = ] [ 2drop 2drop { } ] }

{ [ 2dup < ] [ 2drop [ 1 cut ] dip

[ 1- among [ append ] with map ]

[ among append ] 2bi

] }

{ [ 2dup = ] [ 3drop 1array ] }

{ [ 2dup > ] [ 2drop 2drop { } ] }

} cond

;

so again

[ 20 20 <array> 20 [ among ] with each ] time

=> 8953 ms run / 4142 ms GC time

and after

[ 20 20 <array> 20 [ combinations ] with each ] time

=> 20500 ms run / 6359 ms GC time

I tried several times to be sure !

for "10 10 <array> 10" results are equals to 16 ms but for "large number" Eric's nice word is twice slower than mine.

WHY ?

Are there rules to optimise a word ?

On what point must we focus to build efficient code ?

-------------------------------------------------------------------------
This SF.net email is sponsored by the 2008 JavaOne(SM) Conference 
Don't miss this year's exciting event. There's still time to save $100. 
Use priority code J8TL2D2. 
http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone

_______________________________________________
Factor-talk mailing list
Factor-talk@...
https://lists.sourceforge.net/lists/listinfo/factor-talk