reading job-specifier.scm

[Wensheng Xie]

Hi,

when reading the code of mcron, for example, the file job-
specifier.scm, I noted that the following code

```
(define* (range start end #:optional (step 1))
  "Produces a list of values from START up to (but not including) END.
An
optional STEP may be supplied, and (if positive) only every step'th
value will
go into the list.  For example, (range 1 6 2) returns '(1 3 5)."
  (let ((step* (max step 1)))
    (unfold (λ (i) (>= i end))          ;predicate
            identity                    ;value
            (λ (i) (+ step* i))         ;next seed
            start)))                    ;seed
```

I want to understand what is the advantage here. Why don't you write it
like

```
(define* (range start end #:optional (step 1))
  "Produces a list of values from START up to (but not including) END.
An
optional STEP may be supplied, and (if positive) only every step'th
value will
go into the list.  For example, (range 1 6 2) returns '(1 3 5)."
  (let ((step* (max step 1)))
    (if (>= start end)
        '()
        (cons start (range (+ start step*) end step*))))
```

best regards,
wxie

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