chickadee » transducers » zip-range

A transducer that interleaves a range in between items from the current transduction. If there aren't enough elements in either the current transduction or the range being zipped then the transducer exits early.

 
(import transducers)

(transduce list-fold
           (zip-range (range 0 4))
           (collect-list)
           (list 'a 'b 'c))

; => ((a . 0) (b . 1) (c . 2))

Admittedly this is very much like enumerate. However, note that enumerate will have the following differences:

1. enumerate pairs the number and transduced item in the reverse order (e.g. (0 . a) instead of (a . 0))
2. enumerate only terminates when the rest of the transduction does.

Of course, if one feels strongly about the enumerate ordering they are more than welcome to do the following:

 
(import transducers)

(transduce list-fold
           (zip-range (counter 0))
           (collect-list)
           (list 'a 'b 'c))

; => ((a . 0) (b . 1) (c . 2))

Which is equivalent to enumerate except with reversed ordering (since counter is infinite and does not exhaust).