chickadee » transducers » fixnum-range-fold

A folding operation that operates over numeric-range? records. The former (range-fold) is the more generic version of the two, in that it does not require that the ranges be composed of fixnums. The latter (fixnum-range-fold) is only valid for ranges that will iterate over fixnums.

 
(import transducers)

(transduce range-fold
           (take 5)
           (collect-list)
           (counter 1.5 2))

; => (1.5 3.5 5.5 7.5 9.5)

Whereas with fixnum-range-fold you will find that the above transduction fails:

 
(import transducers)

(transduce fixnum-range-fold
           values
           (collect-list)
           (iota 5 1.5 2))

; Error: (fixnum-range-fold) bad argument type - not a fixnum: 1.5
;
;         Call history:
;
;         <syntax>          (transduce fixnum-range-fold values (collect-list) (iota 5 1.5 2))
;         <syntax>          (iota 5 1.5 2)
;         <eval>    (transduce fixnum-range-fold values (collect-list) (iota 5 1.5 2))
;         <eval>    (iota 5 1.5 2)        <--

The advantage of fixnum-range-fold is that it is faster than range-fold when your have a finite range (from range or iota) consisting only of integers. This is often the fastest way to iterate through over a set of indices.