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f. Improved initial writing: 2003-07-14
last updated: 2004-10-26

f. has been improved so that v f. would exploit the special code that would be exploited by a completely primitive version of v ; the execution of x v f. y (and v f. y) would be as fast and as lean as a completely primitive version of v . For example:

   ts=: 6!:2 , 7!:2@]   NB. time and space

   tally =: #
   rev=: |.
   x=: 100000 $ i. 6
   y=: i. 100000 10

   ts 'Expression'
Expression    J 5.03   J 5.02   Ratio
x #/. y  0.0114327   1.57370e6  0.0114442   1.57370e6
x tally/. y  0.114467 1.32402e7  0.115316 1.32402e7
x tally/.f. y  0.0117163 1.57414e6  0.0763963 6.94848e6  6.52 4.41
|."1 y  0.0383105 4.19520e6  0.0383065 4.19520e6
rev"1 y  0.193694 4.19578e6  0.183509 4.19578e6
rev"1 f. y  0.0380708 4.19558e6  0.0994439 4.19603e6  2.61 1.00


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