Closures

Ruby
1

hi

i’m having a little trouble with closures and i’d like to know what
the equivalent code for the canonical make-adder procedure would in
ruby,

in scheme it would be like

(define (make-adder n)
(lambda (x) (+ x n))

thanks in advance

2

Hi Burlsm,

I think the following is what you want:

def make_adder(n)
lambda { |x| x + n }
end

or the following new lambda syntax if you are using Ruby 1.9 or later:

def make_adder(n)
->(x) { x + n }
end

Hope that helps.

allenlooplee

3

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On a sidenote, Ruby 1.9 also has this cool function:

f = ->(a,b){ a + b }
c = f.curry
b = c[1]

where b is a partially applied function, with a bound to 1.

b[6] #=> a + b = 7

then evaluates the whole function.

Regards,
Florian

P.S.: I still think it should be called #schönfinkeln.

On Nov 28, 2009, at 2:47 AM, Allen L. wrote:

def make_adder(n)

hi
thanks in advance

Florian G.

smtp: [email protected]
jabber: [email protected]
gpg: 533148E2

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4

Burlsm wrote:

hi

i’m having a little trouble with closures and i’d like to know what
the equivalent code for the canonical make-adder procedure would in
ruby,

in scheme it would be like

(define (make-adder n)
(lambda (x) (+ x n))

thanks in advance

I noticed this link describing some scheme style closures in ruby
http://innig.net/software/ruby/closures-in-ruby.rb
in the ruby talk faq the other day.
-r

5

2009/11/28 Florian G. [email protected]:

b[6] #=> a + b = 7

then evaluates the whole function.

The cool thing is that the result of f.curry can be used to curry the
function as well as to evaluate it - depending on the number of
arguments:

irb(main):001:0> f = ->(a,b){ a + b }
=> #<Proc:0x101731c0@(irb):1 (lambda)>
irb(main):002:0> f[1,2]
=> 3
irb(main):003:0> c = f.curry
=> #Proc:0x10169d28
irb(main):004:0> c[1,2]
=> 3
irb(main):005:0> b = c[1]
=> #Proc:0x10159cc0
irb(main):006:0> b[2]
=> 3
irb(main):007:0>

P.S.: I still think it should be called #schönfinkeln.

LOL

Kind regards

robert