Arc Forum | Here's an alternative version of a step macro: (mac step (v init end by . body)...

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1 point by skenney26 5466 days ago | link | parent

Here's an alternative version of a step macro:

  (mac step (v init end by . body)
    (w/uniq (gi ge gtest gupdate)
     `(withs (,v nil ,gi ,init ,ge ,end
              ,gtest   (if (< ,gi ,ge) <= >=)
              ,gupdate (if (< ,gi ,ge) + -))
        (loop (set ,v ,gi)
              (,gtest ,v ,ge)
              (set ,v (,gupdate ,v ,by))
          ,@body))))

1 point by thaddeus 5466 days ago | link

A much better alternate version too. The redundant code in my hacked version was obvious and ugly, but I struggled reducing it to a simpler form... Thanks!

I made a few slight adjustments though, as it failed 2 of my test cases (however unlikely they are to occur, infinite runs scare me).

    (mac step (v init end by . body)
     (if (isnt by 0) 
       (w/uniq (gi ge gtest gupdate)
        `(withs (,v nil ,gi ,init ,ge ,end
                 ,gtest   (if (< ,gi ,ge) <= >=)
                 ,gupdate (if (< ,gi ,ge) + -))
           (loop (set ,v ,gi)
                 (,gtest ,v ,ge)
                 (set ,v (,gupdate ,v (abs ,by)))
             ,@body))) nil ))

now passes these two test cases:

    (step i 5 10 -2 (prn i))
    (step i 0 1 0 (prn i))

Thanks! T.

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