RSS 2.0
Sign In
# Sunday, April 8, 2012

Several days ago we've arrived to the blog "Recursive lambda expressions". There, author asks how to write a lambda expression that calculates a factorial (only expression statements are allowed).

The problem by itself is rather artificial, but at times you feel an intellectual pleasure solving such tasks by yourself. So, putting original blog post aside we devised our answers. The shortest one goes like this:

  1. As C# lambda expression cannot refer to itself, so it have to receive itself as a parameter, so:
    factorial(factorial, n) = n <= 1 ? 1 : n * factorial(factorial, n - 1);
  2. To define such lambda expression we have to declare a delegate type that receives a delegate of the same type:
    delegate int Impl(Impl impl, int n);
    Fortunately, C# allows this, but a workaround could be used even if it were not possible.

  3. To simplify the reasoning we've defined a two-expression version:
    Impl impl = (f, n) => n <= 1 ? 1 : n * f(f, n - 1);
    Func<int, int> factorial = i => impl(impl, i);
  4. Finally, we've written out a one-expression version:
    Func<int, int> factorial = i => ((Func<Impl, int>)(f => f(f, i)))((f, n) => n <= 1 ? 1 : n * f(f, n - 1));
  5. The use is:
    var f = factorial(10);

After that excercise we've returned back to original blog and compared solutions. We can see that author appeals to a set theory but for some reason his answer is more complex than nesessary, but comments contain variants that analogous to our answer.

Sunday, April 8, 2012 9:18:29 AM UTC  #    Comments [0] -
.NET | Tips and tricks
All comments require the approval of the site owner before being displayed.
Name
E-mail
Home page

Comment (Some html is allowed: a@href@title, b, blockquote@cite, em, i, strike, strong, sub, super, u) where the @ means "attribute." For example, you can use <a href="" title=""> or <blockquote cite="Scott">.  

[Captcha]Enter the code shown (prevents robots):

Live Comment Preview
Archive
<April 2012>
SunMonTueWedThuFriSat
25262728293031
1234567
891011121314
15161718192021
22232425262728
293012345
Statistics
Total Posts: 305
This Year: 18
This Month: 2
This Week: 0
Comments: 207
Locations of visitors to this page
Disclaimer
The opinions expressed herein are our own personal opinions and do not represent our employer's view in anyway.

© 2014, Nesterovsky bros
All Content © 2014, Nesterovsky bros
DasBlog theme 'Business' created by Christoph De Baene (delarou)