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CS 320: Compiling Techniques
David Walker
People David Walker (Professor)
412 Computer Science Building [email protected] office hours: after each class
Guilherme Ottoni (TA) 417 Computer Science Building [email protected] office hours:
Mondays 2-2:30 PM Fridays 2-3 PM
Information Web site:
www.cs.princeton.edu/courses/archive/spring05/cos320/index.htm
Mailing list: To subscribe:
[email protected] To post to this list, send your email to:
Books Modern Compiler Implementation
in ML, Andrew Appel
A reference manual for SML best choice: Online references
see course web site several hardcopy books
Elements of ML Programming, Jeffrey D. Ullman
Assignment 0 Write your name and other
information on the sheet circulating Find, skim and bookmark the course
web pages Subscribe to course e-mail list Begin assignment 1
Figure out how to run & use SML Due next Thursday February 10
onward!
What is a compiler? A compiler is program that
translates a source language into an equivalent target language
What is a compiler?
while (i > 3) { a[i] = b[i]; i ++}
mov eax, ebxadd eax, 1cmp eax, 3jcc eax, edx
C program
assemblyprogram
compiler does this
What is a compiler?
class foo { int bar; ...}
struct foo { int bar; ...}
Java program
compiler does this
C program
What is a compiler?
class foo { int bar; ...}
........
.........
........
Java program
compiler does this
Java virtual machine program
What is a compiler?
\newcommand{....}
\sfd\sf\fadg
Latex program
compiler does this
Tex program
What is a compiler?
\newcommand{....}
\sfd\sf\fadg
Tex program
compiler does this
Postscript program
What is a compiler? Other places:
Web scripts are compiled into HTML assembly language is compiled into
machine language hardware description language is
compiled into a hardware circuit ...
Compilers are complex text file to abstract
syntax lexing; parsing
abstract syntax to intermediate form (IR) analysis; optimizations;
data layout
IR to machine code code generation;
register allocation
front-end
middle-end
back-end
Course project Fun Source Language
simple imperative language
Only 1 IR (the initial abstract syntax generated by the parser)
type checking; high-level optimizations
Code Generation instruction selection algorithms;
register allocation via graph coloring
front-end
middle-end
back-end
Standard ML Standard ML is a domain-specific
language for building compilers Support for
Complex data structures (abstract syntax, compiler intermediate forms)
Memory management like Java Large projects with many modules Advanced type system for error
detection
Introduction to ML You will be responsible for learning
ML on your own. Today I will cover some basics
Resources: Robert Harper’s Online book “an
introduction to ML” is a good place to start
See course webpage for pointers and info about how to get the software
Intro to ML Highlights
Data Structures for compilers Data type definitions Pattern matching
Strongly-typed language Every expression has a type Certain errors cannot occur Polymorphic types provide flexibility
Flexible Module System Abstract Types Higher-order modules (functors)
Intro to ML Interactive Language
Type in expressions Evaluate and print type and result Compiler as well
High-level programming features Data types Pattern matching Exceptions Mutable data discouraged
Preliminaries start sml in Unix by typing sml
at a prompt:
tux% smlStandard ML of New Jersey, Version 110.0.7,
September 28, 2000 [CM; autoload enabled]-
(* quit SML by pressing ctrl-D *)(* just so you know, comments can be (* nested *)
*)
Preliminaries Read – Eval – Print – Loop
- 3 + 2;
Preliminaries Read – Eval – Print – Loop
- 3 + 2;> 5: int
Preliminaries Read – Eval – Print – Loop
- 3 + 2;> 5: int- it + 7;> 12 : int
Preliminaries Read – Eval – Print – Loop
- 3 + 2;> 5: int- it + 7;> 12 : int- it – 3;> 9 : int- 4 + true;
stdIn:17.1-17.9 Error: operator and operand don't agree [literal]
operator domain: int * int operand: int * bool in expression: 4 + true
Preliminaries Read – Eval – Print – Loop
- 3 div 0;Failure : Div run-time error
Basic Values- ();> () : unit => like “void” in C (sort of)
=> the uninteresting value/type
- true;> true : bool- false;> false : bool- if it then 3+2 else 7; “else” clause is always necessary> 7 : int- false andalso loop_Forever;> false : bool and also, or else short-circuit eval
Basic ValuesIntegers- 3 + 2;> 5 : int- 3 + (if not true then 5 else 7);> 10 : int No division between expressions
and statementsStrings- “Dave” ^ “ “ ^ “Walker”;> “Dave Walker” : string- print “foo\n”;foo> 3 : int
Reals- 3.14;> 3.14 : real
Using SML/NJ Interactive mode is a good way to
start learning and to debug programs, but…
Type in a series of declarations into a “.sml” file
- use “foo.sml”[opening foo.sml]…
list of declarationswith their types
Larger Projects SML has its own built in interactive
“make” Pros:
It automatically does the dependency analysis for you
No crazy makefile syntax to learn Cons:
May be more difficult to interact with other languages or tools
Compilation Manager
% sml
- OS.FileSys.chDir “~/courses/510/a2”;
- CM.make(); looks for “sources.cm”, analyzes dependencies
[compiling…] compiles files in group
[wrote…] saves binaries in ./CM/
- CM.make’ “myproj/”(); specify directory
sources.cmc.smlb.smla.sigGroup is
a.sigb.smlc.sml
What is next? ML has a rich set of structured values
Tuples: (17, true, “stuff”) Records: {name = “Dave”, ssn = 332177} Lists: 3::4::5::nil or [3,4]@[5] Datatypes Functions And more!
Rather than list all the details, we will write a couple of programs
An interpreter Interpreters are usually
implemented as a series of transformers:
stream ofcharacters
abstractsyntax
lexing/parsing
evaluate
abstractvalue
stream ofcharacters
A little language (LL) An arithmetic expression e is
a boolean value an if statement (if e1 then e2 else e3) an integer an add operation a test for zero (isZero e)
LL abstract syntax in ML
datatype term = Bool of bool| If of term * term * term| Num of int| Add of term * term| IsZero of term
-- by convention, constructors are capitalized
-- constructors can take a single argument of a particular type
type of a tupleanother eg: string * char
vertical barseparates alternatives
LL abstract syntax in ML
Add (Num 2, Num 3)
represents the expression “2 + 3”
Add
Num Num
2 3
LL abstract syntax in ML
If (Bool true, Num 0, Add (Num 2, Num 3))
represents
“if true then 0 else 2 + 3”
Add
Num Num
2 3
true
Bool Num
0
If
Function declarations
fun isValue t = case t of Num n => true | Bool b => true | _ => false
function name function parameter
default pattern matches anything
What is the type of the parameter t? Of the function?
fun isValue t = case t of Num n => true | Bool b => true | _ => false
function name function parameter
default pattern matches anything
What is the type of the parameter t? Of the function?
fun isValue (t:term) : bool = case t of Num n => true | Bool b => true | _ => false
val isValue : term -> bool
ML does type inference => you need notannotate functions yourself (but it can be helpful)
A type error
fun isValue t = case t of Num n => n | _ => false
ex.sml:22.3-24.15 Error: types of rules don't agree [literal] earlier rule(s): term -> int this rule: term -> bool in rule: Successor t2 => true
A type error
Actually, ML will give you several errors in a row:
ex.sml:22.3-25.15 Error: types of rules don't agree [literal] earlier rule(s): term -> int this rule: term -> bool in rule: Successor t2 => trueex.sml:22.3-25.15 Error: types of rules don't agree [literal] earlier rule(s): term -> int this rule: term -> bool in rule: _ => false
A very subtle error
fun isValue t = case t of num => true | _ => false
The code above type checks. But whenwe test it refined the function always returns “true.”What has gone wrong?
A very subtle error
fun isValue t = case t of num => true | _ => false
The code above type checks. But whenwe test it refined the function always returns “true.”What has gone wrong?-- num is not capitalized (and has no argument)-- ML treats it like a variable pattern (matches anything!)
Exceptions
exception Error of string
fun debug s : unit = raise (Error s)
Exceptions
exception Error of string
fun debug s : unit = raise (Error s)
- debug "hello";
uncaught exception Error raised at: ex.sml:15.28-15.35
in SML interpreter:
Evaluator
fun isValue t = ...
exception NoRule
fun eval t = case t of Bool _ | Num _ => t | ...
Evaluator
...
fun eval t = case t of Bool _ | Num _ => t | If(t1,t2,t3) => let val v = eval t1 in case v of Bool b => if b then (eval t2) else (eval t3) | _ => raise NoRule end
let statementfor rememberingtemporaryresults
Evaluatorexception NoRule
fun eval1 t = case t of Bool _ | Num _ => ... | ... | Add (t1,t2) => case (eval v1, eval v2) of (Num n1, Num n2) => Num (n1 + n2) | (_,_) => raise NoRule
Finishing the Evaluatorfun eval1 t = case t of ... | ... | Add (t1,t2) => ... | IsZero t => ...
be sure yourcase isexhaustive
Finishing the Evaluatorfun eval1 t = case t of ... | ... | Add (t1,t2) => ... What if we
forgot a case?
Finishing the Evaluator
ex.sml:25.2-35.12 Warning: match nonexhaustive (Bool _ | Zero) => ... If (t1,t2,t3) => ... Add (t1,t2) => ...
fun eval1 t = case t of ... | ... | Add (t1,t2) => ... What if we
forgot a case?
Last Things Learning to program in SML can be
tricky at first But once you get used to it, you
will never want to go back to imperative languages
Check out the reference materials listed on the course homepage
