CS 655: Programming Languages
Lecture 1:Wherefore CS655?
The use of <???> cripples the mind;
its teaching should, therefore, be
regarded as a criminal offence.
Edsger W.Dijkstra, 1975
David Evans
University of Virginia
Computer Science
Office 236A, 982-2218
evans@cs.virginia.edu
http://www.cs.virginia.edu/~evans
Menu
• Course Logistics: details on Syllabus
• Goals for the Course
• Course Overview, Programming Language
Design
Don’t leave until I take your picture!
Send registration email by tomorrow
Position Paper 1 due Monday.
20 Jan 2000
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Resources
• Staff:
– Instructor: David Evans
evans@cs.virginia.edu
Office Hours (?): Monday 1:302:30,Thursdays after class
– TA: John Haskins, Jr.
predator@cs.virginia.edu
• Email: cs655-staff@cs.virginia.edu
• Web: http://www.cs.virginia.edu/~cs655
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Assignments
• Assigned Readings
• Position Papers (6 or 7)
• Problem Sets (4)
– Technical questions, short answers, not much
coding
• Project
– Work in groups (2-4, solo projects only in unusual
circumstances)
– List of ideas (projects/ideas.html)
– Start thinking about this now – request teammates
on registration survey
• Oral Final Exam
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Position Papers
• Not book reports
• Be provocative and interesting
– Should make claims reasonable people could
disagree with
– Support your claims with technical arguments
• Writing clearly matters, writing clearly matters
• Not longer than the Declaration of
Independence (see ~cs655/papers/papertemplate.html)
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Position Papers Grading
grade  0
{ grade.value = 0 }
|  modifiers { grade.value = modifiers.value }
modifiers   { modifiers.value = 1 }
| + modifiers { modifiersL.value = modifiersR.value * 2 }
| - modifiers {modifiersL.value = modifiersR.value * 1/2 }
• Hard to get + (few per assignment), really
hard to get ++ (few per term), etc.
• If unhappy with grade, can submit 1 page
response. Grade can go up or down as a
result.
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Position Papers Logistics
• Use HTML template
• Turn in by emailing URL and copy of
contents to cs655-staff@cs.virginia.edu
• Pay attention to weird due times:
First Position Paper is due Monday at
11:59pm.
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How to get an A in CS655
• “Easy” way: Convince an established
language designer to make a substantive
change to a programming language
• “Hard” way
Course Project (30%) Position papers (30%)
Exam (20%)
Problem Sets (20%)
Class Participation (0%, but important)
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Honor Code, Schmonor Code
• Learn from your fellow students – they are
your best resource!
• Everything you turn in should be your own
• Write down who you discussed assignments
with, all external sources you used
• Be honest – you know what cheating is and
isn’t
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Logistics
Questions
Next: My Goals for the Course
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Goal #1
When you need to invent
a language (and most of
you will at some point in
your career) you will
design it, not just make it
up.
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What’s the difference?
Designed
Just Made Up
Examples
Esperanto, CLU English, C++
Properties
Predictable
Unpredictable
Ways to do
something
One
Many
Users
~1M, 2.5
~1B, ~1M
Moral? A bigger army beats good design every time
But, good designs can influence people with armies
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Goal #2
When you design your
language, you will have
sufficient knowledge of other
languages not to repeat their
mistakes, and solid enough
theory background to describe
your language well.
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Goal #3
You will become better at
programming and building
systems. You will think more
clearly and maybe even write
better.
A language that doesn't affect the way you think
about programming, is not worth knowing.
Alan Perlis
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Goal #4
Some of you will do projects
that lead to conference
papers or thesis topics. All
of you will be able to
understand nearly all PLDI
papers and many POPL
papers.
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Goal #5
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Disclaimer
• Sorry, no refunds if not all goals
are satisfied.
• Tell me your goals on the
survey.
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Course Overview
•
•
•
•
What is a programming language?
What makes a language important?
Design Tradeoffs
Contents of the course
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What is a language?
Webster:
A systematic means of communicating ideas or
feelings by the use of conventionalized signs,
sounds, gestures, or marks having understood
meanings.
Nerdy Linguist’s Definition:
A description of pairs (S, M), where S stands for
sound, or any kind of surface forms, and M stands
for meaning. A theory of language must specify the
properties of S and M, and how they are related.
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What is a Programming Language?
• Bruce MacLellan’s definition:
A language that is intended for the expression
of computer programs and that is capable of
expressing any computer program.
• Ravi Sethi’s definition:
Notations used for specifying, organizing, and
reasoning about computations.
• Liberal definition:
A language (according to the nerdy linguist’s
definition) intended to be read and written by
humans and processed by machines
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What makes a PL important?
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Lots of People Learn It
100
Java
HTML
1000
Eiffel
Pascal
Ada
Lisp
FORTRAN
COBOL
Tcl
C++
C
Basic
10000
No books in print:
Algol60, CLU, Simula
100000
Amazon.com sales rank for best-selling book related to language
(30 November 1999)
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You Can Get a Job
1000
HTML
Basic
Java
C++
100
Pascal
FORTRAN
No job listings:
Algol60, CLU, Simula
Tcl
Ada
COBOL
10
1
Monster.com job listings in Virginia matching language
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(30 November 1999)
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Changes How Programmers Think
Influences other Languages
•
•
•
•
•
FORTRAN - use a high level language
Algol60 - program in a structured way
Simula - use classes
CLU - use data abstraction
FP - program without state
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Language Design as Engineering
Safety
Performance
Java, CLU
FORTRAN, BLISS, C
Ease of Use
BASIC, CLU
Ease/size of Implementation
Forth, C
Orthogonality
Safety, Simplicity
Algol68
Pascal
Simplicity
Expressiveness
Scheme
Common LISP
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Example:
Is assignment an expression?
• Wulf (BLISS): Of course, everything is
• Richie (C): Yes, why not
• Wirth (Pascal): No, only math-like things
are expressions
Who’s right?
What were their design tradeoffs?
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Language Design as Art
• Aesthetics matter
• Readability is usually more important
than Writability
– CLU vs. APL
• Intuitive meaning more important than
formal semantics
– But formal semantics necessary to make
sure we agree on intuitive meaning
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Language as Art: Example
HELLO: PROCEDURE
OPTIONS (MAIN);
FLAG = 0;
LOOP:
DO WHILE (FLAG = 0);
PUT SKIP DATA
('HELLO WORLD!');
END LOOP;
END HELLO;
20 Jan 2000
start_up = proc()
outstream:stream := primary_output()
for s:string in get_hello_world() do
stream$putl(outstream,s)
end
end
get_hello_world = iter() yields(string)
while (true) do yield ("Hello, World!")
end
end
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Interaction of Art & Engineering
Example: C
void test (int x) {
while (x = 1) {
printf (“I’m an imbecile!”);
x = x + 1;
}
}
Art: use = for assignment (not :=)
Engineering: make assignments expressions,
no Boolean type, weak types, etc.
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Structure of the Course
• Balance between:
– History: analyze programming languages
according to design principles
– Theory: tools for analyzing and describing
what programs mean
– Research: look at current research and
discuss open problems
• Class as good as you make it:
– Come to lecture prepared to discuss
readings
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Course Overview
• This course is not
– A humanities course (though at times it
may seem like one)
– A theory course (though at times it may
seem like one)
– A “ripping on C++” course (though at times
it may seem like one)
• It is really about design
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Charge
• Don’t leave until I take your picture
• Think about projects and teams
• Send me your registration survey by
tomorrow
• Turn in position paper by Monday
midnight - be bold!
• Next time: Intro to Semantics
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