It’s possible to use function composition and modify the type of value returned.  Consider the following equation:

1/4x²

I might encode the function to calculate this like so:

let square x = x * x

//Want this to be a float because if this is an int division

// it will always round to 0 if x is greater than 1.

let recip x = 1.0/x

let myFunc =  fun x -> 4* (square x) >> recip

This function composition will not work because I need to pass a float to recip. But I can make it work by doing this:

let square x = x * x

let recip x = 1.0/x

let myFunc = fun x -> 4* (square x) >> float >> recip

There’s a great deal more information on conversion functions in F# here.

Even though tuples, records and discriminated unions are reference types, they all have the built-in equality properties you would expect in a value type.  For example:

> let a = (1,'a');;

val a : int * char = (1, 'a')

> let b = (1,'a');;

val b : int * char = (1, 'a')

> a = b;;

val it : bool = true

That is, you get the equality behavior you would expect rather than the usual equality behavior associated with reference types.  Here’s an example of records and the built-in equality checking:

> type rec1 = {

a:int

b:string

};;

type rec1 =

{a: int;

b: string;}

> let a = {a=1;b="one"};;

val a : rec1 = {a = 1;

b = "one";}

> let b = {a=1;b="one"};;

val b : rec1 = {a = 1;

b = "one";}

> a = b;;

val it : bool = true

The F# developer can use pattern matching syntax pretty much anywhere in F#.  For example, consider the following list:

let l = [1..25]

If I want to get the last element of the list, I can do this with a little trivial pattern match:

let lastElem::_ = l |> List.rev;;

stdin(7,5): warning FS0025: Incomplete pattern matches on this expression. For example, the value '[]' may indicate a case not covered by the pattern(s).

val lastElem : int = 25

In this case, you can safely ignore the warning.

You can also pull one of the elements from a tuple very easily with this pattern match:

let name,_ = (“Onorio”,”11W”);;

val name : string = "Onorio"

The underscore character in both of these pattern matches functions as a wildcard.  In both cases it signifies a value that we don’t care about.

So back in 2011 I was trying to get an F# user group going here in Detroit.  As is so often the case with user groups, most of the responsibility for setting things up and arranging things was falling on one person–me.  In fairness, the folks at Epitec did their best to help; they provided us a place to meet and they provided food.  Still I was the one always doing the presentations and, as anyone who’s ever run a user group knows, that burns a person out in short order.

Still I really wanted people to know the F# story; I think it’s very compelling.  Fast forward to 2012 when I joined John Fair at Quicken Loans.  John is another F#anatic (to coin an unnecessary neologism). John and I have both been running a weekly F# learning session for quite some time.  So yesterday I felt it’s time to apply some of what I’ve learned since 2011 and give another try to running an F# user group here in Detroit.  John has graciously agreed to help and I know that means I won’t be stuck doing all the heavy lifting.

We’re meeting on August 22; location is still to be determined as is the topic of the first meeting.  But either way, I am excited to once again be able to start sharing the F# goodness.  And there is a lot of goodness there.

http://www.meetup.com/Detroit-F-Meetup/