1.1.6 defining a procedure that computes the absolute value of a number

Section 1.1.6 of SICP presents the math rule

"absolute value of a number".SICP present

a couple of implementations of it, both using 

case analysis with cond and if-boolean branching.

This exercise should be a case of pattern

matching.I like F# pattern matching a lot.Unlike 

other functional concepts,(e.g: Curried functions)

hadn't any problem understanding matching.

Certainly it's a powerful tool. You can

think of keyword match Foo with as C#'s swich 

statement done the right way.

let abs x =
   match x with
    | x when x > 0 -> x       //match only when x > 0
    | x when x = 0 -> 0       //match only when x = 0
    | x when x < 0 -> (-x)    //match only when x < 0
    ;;

To test it evaluate the following expresions with REPL

let  absTestA = abs -3
let  absTestB = abs  5
let  absTestC = abs  0

And REPL will return:

 val absTestA : int = 3

 val absTestB : int = 5
 val absTestC : int = 0