Programming Languages and Techniques (CIS120) Lecture 2, Lecture notes of Programming Languages

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Programming Languages

and Techniques

(CIS120)

Lecture 2

January 17, 2013

Value-­‐Oriented Programming

If you are joining us today…

• See Wed’s slides/screencast on course website

• Read the course syllabus/lecture notes on the

website

• Sign yourself up for Piazza

hPp://www.piazza.com/

• Install OCaml/Eclipse on your laptop; ask if you have

quesWons

hPp://www.seas.upenn.edu/~cis120/current/

ocaml_setup.shtml

• No laptops, tablets, smart phones, etc., during

lecture

Announcements

• Please read:

• Chapter 2 of the course notes
• OCaml style guide on the course website (hPp://www.seas.upenn.edu/~cis120/current/ programming_style.shtml)

• Homework 1: OCaml Finger Exercises

• PracWce using OCaml to write simple programs
• Start with first 4 problems (lists next week!)
• Due: Tuesday, January 28 th at 11:59:59pm (midnight)
• Start early!

• Guest lecturer (Peter-­‐Michael Osera) next week

• Prof. Weirich OH Monday, then away Tuesday-­‐Saturday

Homework Policies

• Projects will be (mostly) automaWcally graded
  • We’ll give you some tests, as part of the assignment
  • You’ll write your own tests to supplement these
  • Our grading script will apply addiWonal tests
  • Your score is based on how many of these you pass
  • Some assignments will also include style points, added later
  • Your code must compile to get any credit
• You will be given your score (on the automaWcally graded porWon of the assignment) immediately
• MulWple submissions are allowed
  • First few submissions: no penalty
  • Each submission aker the first few will be penalized
  • Your final grade is determined by the best raw score
• Late submissions
  • 10 point penalty if less than 24 hours late
  • 20 point penalty if 24-­‐48 hours late
  • Submissions not accepted a6er 48 hours past the deadline

Important Dates

• Homework:
  • Homework due dates listed on course calendar
  • Mostly Tuesdays, some Fridays
• Exams:
  • 12% First midterm: Friday, February 21 st , in class
  • 12% Second midterm: Friday, April 4 th , in class
  • 18% Final exam: Wednesday, May 7 th , 9-­‐11 AM
  • Contact me well in advance if you have a conflict

Where to ask quesWons

• Course material

• Piazza Discussion Boards
• TA office hours, on webpage calendar
• Tutoring, Sunday and Monday evenings
• Prof office hours: Mondays from 1 to 3 PM, or by appointment (changes will be announced on Piazza)

• HW/Exam Grading: see webpage

• About the CIS majors

• Ms. Jackie Caliman, CIS Undergraduate coordinator

Clicker Basics

• Beginning today, we’ll use clickers in each lecture

• Grade recording starts 1/

• Any kind of TurningPoint ResponseCard is fine

• Doesn’t have to be the exact model sold in the bookstore

• Use the link on the course website to register your

device ID with the course database

CIS120 6-­‐character device ID

Test Drive

• Clickers out!

• Press any of the number buPons

• Make sure the display looks like this:

• If it looks like this…

• … first check that the channel is set to 41
  • If not, try pressing Channel, then 41, then Channel again to reset the channel
• If this doesn’t work come to office hours

In what language do you have the most significant programming experience?

1. Java C#!
2. C, C#, C++ or Objective-C!
3. Python, Ruby, or MATLAB!
4. Clojure, Scheme, or LISP!
5. OCaML, Haskell, or Scala!
6. Other!

Programming in OCaml

Read Chapter 2 of the CIS 120 lecture notes,

available from the course web page

Value-­‐Oriented Programming

• Java, C, C#, C++, Python, Perl, etc. are tuned for an

impera2ve programming style

• Programs are full of commands
  • “Change x to 5!”
  • “Increment z!”
  • “Make this point to that!”

• Ocaml, on the other hand, promotes a value-­‐

oriented style

• We’ve seen that there are a few commands…
  • e.g., print_endline, run_test … but these are used rarely
• Most of what we write is expressions denoWng values

Metaphorically, we might say that

imperaWve programming is about doing

while

value-­‐oriented programming is about being

What is an OCaml module?

open Assert let attendees (price:int) :int = (- 15 * price) / 10 + 870 let test () : bool = attendees 500 = 120 ;; run_test "attendees at 5.00" test let x = attendees 500 ;; print_int x ;; print_endline "end of demo" module import commands funcWon declaraWons let declaraWons

(Top-­‐level) Let DeclaraWons

A let declaraWon gives a name (a.k.a. an iden;fier ) to

the value of some expression*

There is no way of assigning a new value to an

idenWfier aker it is declared.

let pi = 3. let seconds_per_day = 60 * 60 * 24! *We someWmes call these idenWfiers variables , but the terminology is a bit confusing because in languages like Java and C a variable is something that can be modified over the course of a program. In OCaml, like in mathemaWcs, once a variable’s value is determined, it can never be modified… As a reminder of this difference, for the purposes of OCaml we’ll try to use the word “idenWfier” when talking about the name bound by a let.