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CD5100 Functional Programming

Assignment 1 - Getting started

1) Start up F# on your computer by starting Visual Studio and the F# Interactive Environment by selecting the View -> Other Windows -> F# Interactive menu item.

Enter a few arithmetic expressions at the prompt and press enter to evaluate them. Now try evaluating the expressions listed below:

3 :: [4; 5; 2; 7];;

List.length [4; 5; 2; 7];;

[4; 5; 2; 7] :: 3;;

The evaluation of the last expression generated errors. Why? What would you do to make it work?

2) You can only evaluate expressions that will fit on a single line at the prompt. If you want to write more complex expressions, or declare your own functions, you need to put the code in a file and then load that file into the F# Interactive Environment.

Create the file "Lab1.fs". You can use any text editor you like, but Visual Studio is recommended. Now declare some values in the file, for example:

#light

module Lab1

let x = 42

let myName = "Kalle"

let age = 25

let y = 4 + 2

The #light directive lightens up the syntax requirements. Save the file and load it into the system by writing: #load “c:\\...\\Lab1.fs”;;. You open the module by writing open “Lab1”;;. Then you can inspect the values by simply writing x;;, etc. The file and the module do not have to have the same name; however, it is convenient to do so.

Enter the following declarations into the file and evaluate. What values would b and c hold, and why?

let a = 5;;

let b = let a = 10 in a + 5;;

let c = a + b;;

3) Now it is time to declare some functions.

• Define the function add10, which takes an integer argument, adds 10 to it and returns the result.
• Define the function add20, which uses add10 to add 20 to a given integer.
• Define the function add_mn that takes two integers m, n as arguments and returns m + 10*n. For instance, add_mn 3 5 = 3 + 10*5 = 53. You are, however, not allowed to use multiplication: instead, you must write a recursive solution that calls add10! (So add_mn 3 5 should be computed as 3 + 10 + 10 + 10 + 10 + 10.)

4) Define the function max2 that takes two integers as arguments and returns the largest of them and the function max_list that returns the largest of the elements in a nonempty list of integers by calling max2. For the empty list, it should abort with an error message (raising an exception).

Björn Lisper
bjorn.lisper#mdh.se

(Based on the 2002 version by Lars Bruce)