# Re: Partial functions? **URL:** \ **Category:** Ruby\ **Created:** [May 18, 2006, 5:09pm UTC](https://www.ruby-forum.com/t/re-partial-functions/94976 "2006-05-18T17:09:53Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\ **Post date:** [May 18, 2006, 5:09pm UTC](https://www.ruby-forum.com/t/re-partial-functions/94976/1 "2006-05-18T17:09:53Z")
> > partial functions would be. Can someone provide a use case for me? > > # Convert a 2 arg operator (\*) > > created function a name: > > a\_times\_3 = a.collect { |n| n \* 3 } > > – Jim W. Ah, ok. Is there any kind of speed advantage to this approach? Or is it more of a design/DRY technique? Dan This communication is the property of Qwest and may contain confidential or privileged information. Unauthorized use of this communication is strictly prohibited and may be unlawful. If you have received this communication in error, please immediately notify the sender by reply e-mail and destroy all copies of the communication and any attachments. ---
**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\ **Post date:** [May 18, 2006, 5:36pm UTC](https://www.ruby-forum.com/t/re-partial-functions/94976/2 "2006-05-18T17:36:52Z")
On 5/18/06, Berger, Daniel [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > I’m trying to understand a new feature of Python 2.5 (PEP > > > > 1. called > > > > > “partial functions”. Here’s the Python example I pulled > > > from Vincent > > > Foley’s blog: > > > > [… curry example elided …] I think partial functions is unapropriate name. The first thing I thought of when I read the subject of this email was the mathematical concept of it[0]. > > We do it all the time. We just don’t generally bother to > > give the newly > > created function a name: > > > > a\_times\_3 = a.collect { |n| n \* 3 } > > Ah, ok. Is there any kind of speed advantage to this approach? Or is > it more of a design/DRY technique? I think giving it a name allows you to reuse it multiple times without rewriting it. Everytime you introduce a new name function you have a new abstraction. You could later redefine it (e.g. for speed/space optimization) and that change would propagate to all its uses. Having high order functions is a nice thing to have because you can use them to build complex functions out of simpler ones. I asked a similar question sometime ago[1]. Cheers, Ed [0] [Partial Function -- from Wolfram MathWorld](http://mathworld.wolfram.com/PartialFunction.html) [1] [http://tinyurl.com/rtuuz](http://tinyurl.com/rtuuz) ---
**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\ **Post date:** [May 19, 2006, 4:00am UTC](https://www.ruby-forum.com/t/re-partial-functions/94976/3 "2006-05-19T04:00:18Z")
On 5/18/06, Berger, Daniel [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Ah, ok. Is there any kind of speed advantage to this approach? Or is > it more of a design/DRY technique? In functional languages, the compiler can reduce all the computation involving the curried args, storing the computation. This can make things faster. f x y = (do\_something\_expensive\_with x) + y f\_15 = f 15 # takes a while because reduces # (do\_something\_expensive\_with 15) to a value (1…10000).map(f\_15) # executes very fast In ruby, it makes things slower 🙂 (Two calls instead of one, no caching of results.) ---
**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\ **Post date:** [May 19, 2006, 5:32am UTC](https://www.ruby-forum.com/t/re-partial-functions/94976/4 "2006-05-19T05:32:03Z")
On 5/18/06, Edgardo H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I think partial functions is unapropriate name. The first thing I > thought of when I read the subject of this email was the mathematical > concept of it[0]. Exactly. Partial functions are another term for what some references call ‘recursively enumerable’ functions, meaning a function that can be computed by some Turing machine. I believe the appropriate term is ‘Curried functions’, from the logician who first proposed them, someone called Haskell Curry (yes, _that_ Haskell). I’ve been programming in Ocaml too, and there it seems that curried functions are extremely useful. In Ocaml most often I’ve used it to call a function with several arguments multiple times with only a few arguments changing between calls, or for passing a function with say 4 arguments to an HOF that expects a function with only one, I create a curried function that keeps 3 of the 4 arguments fixed and pass that. Since it is indeed possible to program in the functional style in Ruby, I could imagine that the technique would be just as usable.