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Cse321, Programming Languages and Compilers

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Lecture #1, Jan. 9, 2007Course Mechanics

Text BookDown-loading SML

Syllabus - Course Overview

Entrance Exam

Standard ML

This weeks assignment

Top to bottom example

Lexical issues

Parsing and syntax issues

Translation issues

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Acknowledgements

The material taught in this coursewas made possible by many people.Here is a partial list:

Andrew Tolmach

Nathan Linger Harry Porter

Jinke Lee

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Class Web Page

The CS321 class web page can be

found at:www.cs.pdx.edu/~sheard/course/Cs321

Contents of the page Course Syllabus

Link to the ML home page

Copies of the PowerPoint slides used in lectures

Copies of the assignments

Project Description

Copies of the SML code illustrated in the lectures

The web page will be updated aftereach lecture.

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Todays AssignmentsReading Engineering a Compiler

Available In the PSU bookstore

Chapter 1, pp 1-26

There will be a 5 minute quiz on the reading Wednesday.

Search Find the class webpage

1 page programming Assignment Due Wednesday, Jan 10, 2007. In Just 2 Days!!

Login to some SML system. See how the systemoperates. Type in solutions (in a file) to theprogramming problems (In Class exercises 1 and 2 inthis handout), load them into SML. Get themrunning, and print them out then turn them in onWednesday. What matters here is that you try outthe SML system, not that you get them perfect.

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Course Information CS321 - Languages and Compiler Design

Time: Monday & Wednesday 18:00-19:50 pm

Place: PCAT 138

Instructor: Tim Sheard

office: room 115, CS Dept, 4th Ave Building, Portland State Univ.

phone: 503-725-2410 (work) 503-649-7242 (home)

office hours: Before class in my office (5:00-5:50), or by Appt.

Assignments Reading from text and handouts (quizzes on reading)

Daily, 1 page programming assignments

3 part programming project

Grading: midterm exam (25%)

3 parts of project (30%)

Daily 1 page assignments and quizzes (15%)

Final exam (30 %)

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Examinations

Entrance Exam.

Do you know your REs and CFGs?

Quizzes on Reading Material. There is a possible quiz on every reading assignment

There will be a quiz on Wednesday!

Mid Term exam Wed. Feb 14, 2007. Time: in class.

Final exam Monday, Mar. 19, 2007. Time: 6:00-7:50.

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Text Book

Text: Engineering a Compiler

Keith D. Cooper, and Linda Torczon Other Reference Materials

Auxilliary Material

Elements of Functional Programming (SML book)

by Chris Reade, Addison Wesley, ISBN 0-201-12915-9

Using the SML/NJ Systemhttp://www.cs.cmu.edu/~petel/smlguide/smlnj.htm

Class Handouts Each class, a copy of that days slides will be available as a

handout.

I will post files that contain the example programs used in eachlecture on the class web pagewww.cs.pdx.edu/~sheard/course/Cs321

I will post Assignments there as well.
http://www.cs.pdx.edu/~sheard/course/funproghttp://www.cs.pdx.edu/~sheard/course/funprog

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Labs

Whenever you learn a new language its

great to have someone looking over yourshoulder.

In this spirit I have scheduled some labtimes where people can work on learningML while I am there to help. FAB INTEL Lab (FAB 55-17) downstairs by the Engineering and

Technology Manangements departmental offices

Friday Jan. 12, 2007. 4:00 5:30 PM

Tueday Jan. 16, 2007 4:00 5:30

Friday Jan. 19, 2005. 4:00 5:30 PM

Labs are not required, but attendance of atleast one is highly recommended!

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Installing SML

Software can be obtained at: http://www.smlnj.org/

I am using the most recent version 110.60 but it displays the version 110.57 when it runs

Browse the documentation and Literature sectionof the SML web page. Find some resources that youcan use.

SML also runs on the PSU linux and Intel labs linux

usepkg sml

then logout, or start a new shell

type: sm

Intel In a commnd window

p:\programs\smlnj\addpkg.cmd

then logout, or start a new command window

then just type:

N:\>sml
http://www.smlnj.org/http://www.smlnj.org/http://www.smlnj.org/http://www.smlnj.org/

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Entrance Exam

CS321 has some pretty serious

prerequisites.

Write a regular expression for the set ofstrings that begins with an a which isfollowed by an arbitrary number of bs orcs, and is ended by a d.

e.g. ad, abbbd, abcbcbcd, etc.

2. Transform your regular expression into aDFA

3. Write a context free grammar thatrecognizes the same set of strings as yourRE

4 Transform your CFG into a CFG that is left-

recursion free.

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Academic Integrity

Students are expected to be honest in their

academic dealings. Dishonesty is dealt withseverely.

Homework. Pass in only your own work.

Program assignments. Program independently.

Examinations. Notes and such, only as eachinstructor allows.

OK to discuss how to solveproblems with other students,

but each student should

write up, debug, and turn in his

own solution.

C 321 P i L d C il

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Course Thesis This course is about programming

languages. We study languages in twoways. From the perspective of the user

From the perspective of the implementer (compiler writer)

We will learn about some languages youmay never have heard of. We will learn toprogram in one of them (Standard ML). Itsgood to learn a new language in depth.

This course is also about programming.There will be extensive programmingassignments in SML. If you dont do them -you wont learn Youre deluding yourself if you think you can learn the material

without doing the exercises!

We will write a comiler for a Java subset.Its good to understand the implementation

details of a language you already know.

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This course is all about programming

What makes a good program?

Write at least 3 things on a piece of paper.

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Standard ML

In this course we will use an

implementation of the language StandardML

The SML/NJ Homepage has lots of usefulinformation: http://www.smlnj.org//

You can get a version to install on your ownmachine there.

I will use the version 110.57 or 110.60 of SML. Earlierversions probably will work as well. I dont foresee anyproblems with other versions, but if you want to use theidentical version that I use in class then this is the one.

C 321 P i L d C il
http://www.haskell.org/http://www.smlnj.org/

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Characteristics of SML

Applicative style

input output description of problem. First class functions

pass as parameters

return as value of a function

store in data-structures

Less Importantly: Automatic memory management (G.C. no new or malloc)

Use of a strong type system which uses type inference, i.e. nodeclarations but still strongly typed.

Cse321 Programming Languages and Compilers

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Syntactic Elements

Identifiers start with a letter followed bydigits or other letters or primes orunderscores. Valid Examples: a a3 ab aF

Invalid Examples: 12A

Identifiers can also be constructed with asequence of operators like: !@#$%^&*+~

Reserved words include

fun val datatype if then else

if of let in end type


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Interacting

The normal style for interaction is to start

SML, and then type definitions into thewindow. Types of commands

4 + 5;val x = 34; fun f x = x + 1;

Here are two commands you might finduseful.

val pwd = OS.FileSys.getDir;

val cd = OS.FileSys.chDir;

To load a file that has a sml program type

Use file.sml;


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The SML Read-Typecheck-Eval-Print Loop

Standard ML of New Jersey v110.57 [built: Mon Nov 21 21:46:28 2005]

-

- 3+5;val it = 8 : int

-

- print "Hi there\n";

Hi there

val it = () : unit

-

- val x = 22;

val x = 22 : int

-

- x+ 5;

val it = 27 : int

--

val pwd = OS.FileSys.getDir;-val pwd = fn : unit -> string

- val cd = OS.FileSys.chDir;

val cd = fn : string -> unit

-

Note the semicolon when

youre ready to evaluate.

Otherwise commands can

spread across several

lines.


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fun lastone x = hd (rev x)

fun prefix x = rev (tl (rev x))

In Class Exercise 1 Define prefix and lastone in terms of head tail and

reverse.

First make a file S01code.sml Start sml Change directory to

where the file resides Load the file ( use S01code.html ) Test the function

Standard ML of New Jersey v110.57 - K;- val cd = OS.FileSys.chDir;

val cd = fn : string -> unit

- cd "D:/work/sheard/courses/PsuCs321/web/notes";

- use "S01code.html";

[opening S01code.html]

val lastone = fn : 'a list -> 'aval prefix = fn : 'a list -> 'a list

val it = () : unit

- lastone [1,2,3,4];

val it = 4 : int


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In Class Exercise 2

define map and filter functions

mymap f [1,2,3] = [f 1, f 2, f 3] filter even [1,2,3,4,5] = [2,4]

fun mymap f [] = []

| mymap f (x::xs) = (f x)::(mymap f xs);

fun filter p [] = []

| filter p (x::xs) =

if (p x) then x::(filter p xs) else (filter p xs);

Sample Session

- mymap plusone [2,3,4]

[3, 4, 5]

- filter even [1,2,3,4,5,6]

[2, 4, 6]


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Course topics

Programming Language Types of languages

Data types and languages

Types and languages

Compilers Lexical analysis

Parsing

Translation to abstract syntax using modern parser generatortechnology.

Type checking

identifiers and symbol table organization,

Next Quarter in the second class of thesequence Intermediate representations

Backend analysis

Transformations and optimizations for a number of different kinds

of languages


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Multi Pass Compilers

Passes

text tokens

syntax trees

intermediate forms

(three address code, CPS code, etc)

assembly code machine code

Each phase is from one form to another, ORfrom one form to the same form, which isoften called a source to sourcetransformation.


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The Top to Bottom Example

text:

tokens:

syntax tree:

id(z) eql id(x) plus id(pi) times float(12.0)

z = x + pi * 12.0

+Id(z)

float(12.0)

=

Id(z)

*Id(x)

Id(pi)


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Passes (cont)

Three address code:

temp1 := pi * 12.0z := x * temp1

Assembly level code:

ld r1,x

ld r2,pi

add r1,r2

ldi r2,12.0

mul r1,r2

st r1,z


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Lexical Analysis

Produces Tokens and Deals with:

white space comments

reserved word identification

symbol table interface

Tokens are the terminals of grammars.

Lexical analysis reads the whole program,character by character thus it needs to be

efficient. This implies fancy bufferingtechniques etc. Modern lexical generatorshandle these problems so we will ignorethem.


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Tokens, Patterns & Lexemes

Many strings from the input may produce

the same TOKEN i.e. identifiers, integersconstants, floats

A PATTERN describes a rule which describeswhich strings are assigned to a token.

A LEXEME is the exact sequence of inputcharacters matched by a PATTERN.


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Examples

lexeme pattern token

x * Id "x" abc * Id "abc"

152 + Constant(152)

then then ThenKeyword

Many lexemes map to the same token. e.g.x and abc .

Note, some lexemes might match manypatterns. e.g. "then" above. Need to resolveambiguity.

Since tokens are terminals, they must be"produced" by the lexical phase withsynthesized attributes in place. (e.g. nameof an identifier). e.g. id(x) and

constant(152)


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Syntax, Parse Trees & Grammars

Syntax (the physical layout of the program)

Grammars describe precisely the syntax of a language. Two kindsof grammars which compiler writers use a lot are: regular, andcontext free

Informal Definitions of:

Regular:concatenation, union, star

Context Free:

only one symbol on the lhs of

a production


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Recursive Grammar Examples

Recursive Grammars describe infinitelanguages

list ::= [ num morenum ]

morenum ::= , num morenum

|

derives [ 2 ],[2,4], [2,4,6] ...

Exp ::= id

| Exp + Exp

| Exp * Exp

| ( Exp )derives x x+x


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Parse Trees

Each nonterminal on the lhs of aproduction "roots" a tree:

Each node in a tree with all its immediatechildren is derived from a singleproduction of the grammar

We desire a program which constructs aparse tree from a string. Such programsare different for every grammar, we sometimes use tools to construct suchprograms (yacc).

Ex p

ExpExp +

Id Id


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Syntax Directed Translations

A syntax directed translation traverses asyntax tree and builds a translation in theprocess.

Considerations

Tree Traversal orders Left to right?

right to left?

in-order, pre-order, or post-order

Where does the information about what todo in the traversal come from?

Attribute grammars Inherited attributes

Synthesized attributes


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Example Translation Process

Translation as an abstract syntax to abstractsyntax transformer

We represent this as a grammar with actions{ ... }. The action is performed when thatproduction is reduced.

Exp ::= Term terms

terms ::= + Term { print "+" } term

|

Term ::= Factor factors

factors ::= * Factor { print "*" } factors

|

Factor ::= id { print id.name }


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Semantics

How do we know what to translate thesyntax tree into?

How do we know if it is correct?

Semantics denotational semantics

operational semantics

interpreters

Very useful in writing compilers since theygive a reference when trying to decide what

the compiler should do in particular cases.


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Over view

Compilation is a large process

It is often broken into stages The theories of computer science guide us

in writing programs at each stage.

We must understand what a program

means if we are to translate it correctly. Many phases of the compiler try and

optimize by translating one form into abetter (more efficient?) form.

Most of compiling is about patternmatching languages and tools that supportpattern matching are very useful.

s01 intro ml

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