Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
tmoertel,
Ok - I have to admit that I don't fully understand currying or a lot of other concepts from functional programming (FP). I have a few questions - some in general and some specific to your implementation.

A common way in Perl to simulate currying is as follows:

sub greeting { my ($verb, $object) = @_; my $sub = defined $object ? sub { print "$verb, $object\n" } : sub { print "$verb, ", shift(), "\n" }; return $sub } my $hello = greeting('Happy Birthday', 'L~R'); $hello->(); my $bye = greeting('goodbye'); $bye->('Cruel World'); __END__ Happy Birthday, L~R goodbye, Cruel World
I am guessing the same in a FP language might look like:
greeting('Hello', 'Good Looking'); # prints immediately greeting('Woah'); # Waits ... greeting('Nelly'); # prints now that it has both arguments
How does it know that I am finishing off one and not starting another? Or if the 3rd time I called greeting() I did it with two arguments - what then?

The next question is with your statement:
We can't quite make it all the way because functions in Perl can accept varying numbers of arguments, and thus it's hard for us to determine reliably when currying is implied by analyzing function calls.
Prototypes, as evil as they are, do allow for optional arguments or you could always count @_. I don't see why this is a problem.

My final question for now is an apparent flaw in the design. Currying, as I understand it, only works if I don't have the last x arguments. What if I have the middle argument and the entire function requires 5? In Perl, that would be easy because I would use a hash ref and "name" my arguments. I don't see how currying helps in this situation (real currying, not Perl's substitute).

Thanks by the way - I am impressed.

Cheers - L~R

Update: Added a clarification to distinguish between FP currying and the simulation of currying in Perl


In reply to Re: Near-free function currying in Perl by Limbic~Region
in thread Near-free function currying in Perl by tmoertel

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others taking refuge in the Monastery: (8)
    As of 2020-11-24 21:27 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      No recent polls found

      Notices?