CS150 Notes 2

University of Virginia Computer Science
CS150: Computer Science, Fall 2005

(none)
26 August 2005

CS150 Notes 2 (26 August 2005)

Assignments Due

31 August: Pledge
31 August: Problem Set 1
Monday, 5 September: Read GEB, Little Harmonic Labyrinth and GEB, Chapter 5

Notes and Questions

What is a formal system?

What is the difference between a formal system and a language?

Languages are made of:

Primitives (almost all languages have these) - the simplest surface forms with meaning
Means of Combination (all languages have these) - rules of production (ways to make new surface forms from ones you already have)
Means of Abstraction (all powerful languages have these) - ways to use simple surface forms to represent complicated ones

When learning a foreign language, which of primitives, means of combination or means of abstraction is hardest to learn?

Who was Admiral Grace Hopper and what did she do?

Compiler: A program that translates between two languages, usually from a high-level programming language to machine code.

What is the difference between a compiler and an interpreter?

Why did John Backus want a precise way of describing languages?

Backus Naur Form (BNF): A way of describing the surface forms in a language using replacement rules in the form:

non-terminal ::= replacement

The rule means whenever you have what is on the left side of the ::=, you can replace it with what is on the right side.

What strings can the following BNF grammar produce?

Sentence ::= Food Comparator Food
Food ::= Bodo's Bagels
Food ::= Krispy Kreme Donuts
Comparator ::= are better than
Comparator ::= are worse than

What strings can the following BNF grammar produce?

Sentence ::= I like FoodList
FoodList ::= Food
FoodList ::= Food and FoodList
Food ::= Bodo's Bagels
Food ::= Krispy Kreme Donuts

[Recap from Notes 1] Are there any non-recursive natural languages? What would happen to a society that spoke one?

Links

ENIAC Story (like most ENIAC histories, it is wrong about ENIAC being the "world's first electronic digital computer" — we'll learn why before PS4)
USS Hopper
Remembering Grace Murray Hopper: A Legend in Her Own Time, by Elizabeth Dickason.
John Backus biography
Keynote Speech, First Grace Hopper Conference by Anita Jones

I flunked out every year. I never studied. I hated studying. I was just goofing around. It had the delightful consequence that every year I went to summer school in New Hampshire where I spent the summer sailing and having a nice time.
John Backus (Since you probably don't get to spend the summer in New Hampshire if you flunk out, you may not want to follow his advice here.)

Frankly, we didn't have the vaguest idea how the things would work out in detail... We struck out simply to optimze the object program, the running time, because most people at that time believed you really couldn't do that kind of thing.
John Backus (on FORTRAN language and compiler, quoted in 1966)

"When I use a word," Humpty Dumpty said, in a rather scornful tone, "it means just what I choose it to mean - nothing more nor less."
"The question is," said Alice, "whether you can make words mean so many different things."
"The question is," said Humpty Dumpty, "which is to be master that's all."
Through the Looking Glass — Chapter VI: Humpty Dumpty, Lewis Carroll

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CS 150: Computer Science
University of Virginia

evans@virginia.edu
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