Clojure

• Type: Defect
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: Release 1.4
• Fix Version/s: Release 1.5
• Component/s: None
• Labels:

  • patch
• Environment:

  Mac OS X 10.8.1, Java 1.7.0_06

The when-first macro will evaluate the xs expression twice. Admittedly, it does exactly what the doc string says, but that seems undesirable to me. Even without side effects, there's a potential performance issue if xs is some expensive operation.

Patch attached. The main diff is:

- `(when (seq ~xs)
- (let [~x (first ~xs)]
- ~@body))))
+ `(when-let xs# (seq ~xs)
+ (let ~x (first xs#)
+ ~@body))))

1. 

   0001-avoid-double-evaluation-in-when-first.patch

   04/Sep/12 3:14 PM

   1 kB

   Steve Miner

• Assignee:

  Stuart Sierra

  Reporter:

  Steve Miner

  Waiting On:

  Rich Hickey

• Created:

  04/Sep/12 3:14 PM

  Updated:

  20/Oct/12 9:53 AM

  Resolved:

  20/Oct/12 9:53 AM