HW#1 Getting Started with OCaml Solution

1 Instructions

This assignment will help you set up the tools you need for the class, and gauge your

knowledge of the basics of functional programming. The programming problems are in

Section 3—but read Section 2 first! It will walk you through setting up your OCaml

programming environment. Please don’t hesitate to ask for help on Piazza (https:

//piazza.com/class/jkh8q52qrh06v).

You can submit this assignment through Gradescope (https://www.gradescope.

com).

2 Getting Started with OCaml

OCaml is a functional programming language similar to F#. You can find downloads

and documentation at https://ocaml.org. I recommend installing the OPAM package

manager, and using Emacs or Vim with OCaml extensions to write your code. If you

run into any problems getting started, you can ask for help on Piazza at https://

piazza.com/class/jkh8q52qrh06v. Here are the steps to getting OCaml running on

your computer:

1. Install the OPAM package manager.

On Windows: go to https://fdopen.github.io/opam-repository-mingw/installation/

and download and install the environment. This will give you a new installation

of Cygwin (Unix-style terminal for Windows) with OPAM installed.

On all other platforms: go to https://ocaml.org/docs/install.html and find

the instructions specific to your package manager.

2. Get OCaml extensions for your preferred text editor, as many as you like. I recommend Tuareg (Emacs only) and Merlin (Emacs and Vim). (If you find any other

useful extensions, let the class know on Piazza!) You can install them by running,

e.g., opam install tuareg on the command line. If any more configuration is

needed, it will be mentioned in the output of opam.

3. Try running some OCaml code! You can run ocaml on the command line to start

the interactive read-eval-print loop (REPL). At the # prompt, you can type a line

1

of code ending in ;;, and the REPL will display the results of executing that code.

Try reproducing the following session:

# print_string;;

- : string - unit = <fun

# print_string "Hello world\n";;

Hello world

- : unit = ()

# #quit;;

The OCaml compiler is called ocamlc, and takes files with the extension .ml. Try

writing some code in test.ml (such as print string "Hello world\n";;) and then

running:

ocamlc -o test test.ml

./test

3 Writing OCaml Functions

To receive full credit for the following problems, make sure your code compiles, and do

not use mutable references (i.e., the ref keyword).

1. (3 points) In class, we defined a type intlist of lists of integers as

type intlist = Nil | Cons of int * intlist

Write a function is nil : intlist - bool that is true for Nil and false for

any non-Nil list. For instance, is nil Nil should be true, and is nil (Cons

(1, Nil)) should be false.

2. (3 points) Write a function sum : intlist - int that returns the sum of all the

elements of an intlist. For instance, sum Nil should be 0, and sum (Cons (2,

Cons (3, Nil))) should be 5.

3. (4 points) Define a type int or list that has two constructors: Int, which

takes an int, and List, which takes an intlist. Write a function is pos :

int or list - bool that is true for any positive int and any list whose sum (as

defined in problem 2) is positive, and false otherwise. (A number is positive if it

is greater than 0.) For instance, is pos (Int 0) and is pos (List Nil) should

be false, and is pos (Int 3) and is pos (List (Cons (1, Nil))) should be

true.

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