in reply to Specializing Functions with Currying

good description of currying - it took me ages to understand this concept (through studies of Scheme, Lisp and Haskell over the years), and it didnt finally twig until I was having to extend some legacy C code here - at one point in the code I knew I would eventually call a key function, but I didn't have all the information in scope right then. I remember thinking 'if only I could have a new function that called that one, using the arguments I have now, and the arguments the new function _will_ have in scope when it gets invoked - I could just pass a function pointer to that new function, instead of chaining all these parameters together and passing long parameter lists around...hey!!'

another good name is 'partial application of functions' - your calling it with a partial list of parameters...

any idea how you would do multiple application of these attributes - e.g. bold _and_ italic

use brain;

  • Comment on Re: Specializing Functions with Currying

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Re^2: Specializing Functions with Currying
by Aristotle (Chancellor) on Aug 06, 2004 at 03:12 UTC

    It's not really doable with the simpleminded curry() used here. You'll have to construct this manually.

        'boldital' => do {
        my $i = curry \&wrap_with_html => ( 'i' );
        my $b = curry \&wrap_with_html => ( 'b' );
        sub { $b->( $i->( @_ ) ) }
    },

    [download]

    Makeshifts last the longest.

[reply]
[d/l]
       'boldital' => do {
    my $i = curry \&wrap_with_html => ( 'i' );
    my $b = curry \&wrap_with_html => ( 'b' );
    sub { $b->( $i->( @_ ) ) }
},

      [download]

      Neat use of =>. As for composition, as an inveterate Haskell hacker (well, hacker-wannabe), I'd prefer to have that as a primitive, too: 

      sub compose
{
   my ($f, $g) = @_;

   return sub { $f->($g->(@_)); }
}

# ...

'boldital' => &compose(&curry(\&wrap_with_html, 'i'),
                       &curry(\&wrap_with_html, 'b')),

      [download]
      The idea of functions that operate on functions and return other functions is much more useful than it first seemed to me. If you never think about functions as first-class objects, having a compose function seems incredibly redundant. Once you start building functions on-the-fly, composition becomes indispensible.

      I guess I should write part 2 of my Perlesque Intro to Haskell, then.

      --
      F o x t r o t U n i f o r m
      Found a typo in this node? /msg me
      % man 3 strfry

[reply]
[d/l]
[select]

        Why limit compose to just two functions? 

        sub compose {
    my ($f, $f2, @rest) = @_;
    return $f unless defined $f2;
    return &compose(sub { $f2->($f->(@_)) }, @rest);
}

*bold_italic_and_underlined_paragraph = compose(
    &curry(\&wrap_with_html, 'u'),
    &curry(\&wrap_with_html, 'b'),
    &curry(\&wrap_with_html, 'i'),
    &curry(\&wrap_with_html, 'p')
);

print bold_italic_and_underlined_paragraph("test");

        [download]

        -stvn
[reply]
[d/l]
[select]

        I had seen that some primitive exists for this kind of thing in functional programming, but I have never gotten past a brief foray into that world. My first contact with a number of functional concepts was through Perl, and ever since I've meant to learn a serious functional language. It hasn't happened yet…

        For anyone looking for an introduction to functional concepts in Perl, Mark-Jason Dominus' Higher Order Perl book is well worth a look… or will be once it's finished.

        Makeshifts last the longest.

[reply]
      It's not really doable with the simpleminded curry() used here.
      Perhaps I'm missing something, but what if you did this: 
      my %handler = (
   "bold_italic" =  curry(\&wrap_with_html,"b><i"),
);

      [download]

      thor

      Feel the white light, the light within
      Be your own disciple, fan the sparks of will
      With all of us waiting, your kingdom will come

[reply]
[d/l]

        Err, yes, but that wasn't the point. It's a funny hack, but a hack. :-) It doesn't apply to the general case where one wants to compose functions.

        Makeshifts last the longest.

[reply]
        The closing tag would be incorrect if you just add a slash before the string.
[reply]

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