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Charles Courchaine Still in search of a compelling title & subtitle

But first, a brief introduction as to what prompted this line of posting.  At PDC ‘09 I had the pleasure of making acquaintances with Jon Galloway and Steve Andrews who challenged me to do more than practice & talk with co-workers and put together a talk and the suggested topic for said talk was – functional programming.  Well, I’m not quite at the talk stage yet, but figured that the blog format worked as a good starting point.

So, what is functional programming?  Wikipedia offers the following definition, “In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state. Functional programming has its roots in the lambda calculus, a formal system developed in the 1930s to investigate function definition, function application, and recursion. Many functional programming languages can be viewed as elaborations on the lambda calculus.”  Distilled from Functional Programming for the Real World one is left with the following impression: that functional programming is a declarative style, it promotes immutability, cleaner code & logic organization, functions as data, function composition, and that it’s based on lambda calculus.  That is a highly distilled version of some of the highlights from the first two chapters running about 50 pages.  While both these sketches are accurate, they’re not necessarily helpful in understanding what it is.

At its essence functional programming is another set of tools in the developer’s kit.  For the engineers it’s another hammer for a specific type of material, or a different spanner.  For the artists, it’s another brush.  But because we work outside the confines of the material world our tools aren’t as limited, similarly functional programming isn’t limited to one specific application.  Functional programming is about three different types of tools:

  • A different way of decomposing problems and coming up with solutions – rather than considering objects (data & actions), considering atomic transformations of data and how those fit together.  For example, the pipelining of data in *nix scripts, DOS batch files, or PowerShell, or the IEnumerable extension methods taking in IEnumerable and returning IEnumerable
  • A different way of organizing code to improve readability and comprehension – rather than organizing code around delimiters { } If/End If and classes, organizing around significant whitespace and the transformation to be performed
  • A different language/syntax to better fit a different problem domain – sometimes it makes more sense to look at (F#)
   1: /// The squares of the first 10 integers
   2: let squaresOfOneToTen = [ for x in 0..10 -> x*x ]

compared with (C#)

   1: List<int> squaresOfOneToTen = new List<int>();
   2: for (int x = 0; x < 10; x++)
   3: {
   4:     squaresOfOneToTen.Add(x * x);
   5: }


Like all good tools of the craft, it’s about using the right tool for the right job and functional programming equips you with an array of tools from analysis and design down through code construction.  Functional programming complements object-oriented and procedural programming quite well and is really about making your programs simpler and easier to maintain.  Next up, simplifying and eliminating some duplicate code from a WCF example.

Posted on Monday, January 11, 2010 8:37 PM | Back to top

Comments on this post: Functional Programming: A Gentle Introduction

# re: Functional Programming: A Gentle Introduction
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Here is a FP example in ML, that applies the passed in function to each number starting from n until it reaches 0; and then sums the result:

fun OperateAndSum(f:(int->int),n:int):int =
if n > 0 then
f(n) + OperateAndSum(f,n-1)
Left by Prabhakar Bista on Jan 13, 2010 11:25 AM

# re: Functional Programming: A Gentle Introduction
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Actually, C# is getting more functional all the time. Here is a shorter version of your C# example:

int[] squares = Enumerable.Range(0, 10).Select(x => x*x).ToArray();
Left by Alex Kilpatrick on Jan 13, 2010 5:37 PM

# re: Functional Programming: A Gentle Introduction
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Prabhakar - Thanks for the example in ML!

Dr. Kilpatrick - Absolutely, and that's where the rest of this series focuses and part of what piqued my interest in functional programming was the inclusion of FP constructs in C# (and F#). If you haven't seen it already you should take a look at the Reactive Extensions for .NET (Rx) there's a great series on Bart De Smet's blog about it -

SMiGL - Thanks for the kind words.
Left by Charles Courchaine on Jan 14, 2010 9:37 PM

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