Programming languages

IN4303 2016-2017
Compiler Construction
Programming Languages
imperative & object-oriented
Guido Wachsmuth, Eelco Visser

Imperative and Object-Oriented Languages 2

interpreter
software
language
compiler
software
language
machine
language

Imperative and Object-Oriented Languages
natural
language
natural
language
translator
4
compiler
software
language
machine
language

Traditional compilers
architecture
source
code
errors
parse generate
check
machine
code

Modern compilers in IDEs
architecture
source
code
parse generate
machine
code
check

Compilers are inverted abstractions
architecture
source
code
machine
code
abstract

Compilers Invert Abstractions
Computers speak machine language
• basic instructions to move around and combine small things
Humans do not speak machine language very well
• “mov; loadi; jump” anyone?
Programming languages abstract from machine language
• capture common programming patterns in language constructs
• abstract from uninteresting variation in machines
Compilers invert the abstractions of programming languages
8

Portability: Platform Independence
architecture
source
code
parse
generate
GPU
code
check
generate
x86
code

Understanding Compilers Requires …
Understanding machine languages
• machine architecture, instruction sets
Understanding programming language (abstraction)s
• memory, control-flow, procedures, modules, …
• safety mechanisms: type systems & other static analyses
Understanding how to define mapping from PL to ML
• semantics of such mappings
• techniques to implement such mappings
10

Imperative Languages
state & statements
procedures
types
Object-Oriented Languages
objects & messages
types

state & statements

machine code

basic concepts
State
Machine state
• a pile of data stored in memory
• memory hierarchy: registers, RAM, disk, network, …
Imperative program
• computation is series of changes to memory
• basic operations on memory (increment register)
• controlling such operations (jump, return address, …)
• control represented by state (program counter, stack, …)
14

registers
x86 family
general purpose registers
• accumulator AX - arithmetic operations
• counter CX - shift/rotate instructions, loops
• data DX - arithmetic operations, I/O
• base BX - pointer to data
• stack pointer SP, base pointer BP - top and base of stack
• source SI, destination DI - stream operations
15

registers
x86 family
general purpose registers
• accumulator AX - arithmetic operations
• counter CX - shift/rotate instructions, loops
• data DX - arithmetic operations, I/O
• base BX - pointer to data
• stack pointer SP, base pointer BP - top and base of stack
• source SI, destination DI - stream operations
special purpose registers
• segments SS, CS, DS, ES, FS, GS
• flags EFLAGS
15

mov AX [1]
mov CX AX
L: dec CX
mul CX
cmp CX 1
ja L
mov [2] AX
basic concepts
Example: x86 Assembler
16

read memorymov AX [1]
mov CX AX
L: dec CX
mul CX
cmp CX 1
ja L
mov [2] AX
basic concepts
16

mov CX AX
L: dec CX
mul CX
cmp CX 1
ja L
mov [2] AX
basic concepts
16
write memory

mov CX AX
L: dec CX
mul CX
cmp CX 1
ja L
mov [2] AX
basic concepts
16
write memory
calculation

mov CX AX
L: dec CX
mul CX
cmp CX 1
ja L
mov [2] AX
basic concepts
16
write memory
calculation
jump

.method static public m(I)I
iload 1
ifne else
iconst_1
ireturn
else: iload 1
dup
iconst_1
isub
invokestatic Math/m(I)I
imul
ireturn
basic concepts
Example: Java Bytecode
17

iload 1
ifne else
iconst_1
ireturn
else: iload 1
dup
iconst_1
isub
imul
ireturn
basic concepts
17
read memory

iload 1
ifne else
iconst_1
ireturn
else: iload 1
dup
iconst_1
isub
imul
ireturn
basic concepts
17
read memory
calculation

iload 1
ifne else
iconst_1
ireturn
else: iload 1
dup
iconst_1
isub
imul
ireturn
basic concepts
17
read memory
calculation
jump

basic concepts
Memory & Control Abstractions
Memory abstractions
• variables: abstract over data storage
• expressions: combine data into new data
• assignment: abstract over storage operations
Control-flow abstractions
• structured control-flow: abstract over unstructured jumps
• ‘go to statement considered harmful’ Edgser Dijkstra, 1968
18

states & statements
Example: C
int f = 1
int x = 5
int s = f + x
while (x > 1) {
f = x * f ;
x = x - 1
}
19

states & statements
Example: C
int f = 1
int x = 5
int s = f + x
while (x > 1) {
f = x * f ;
x = x - 1
}
19
variable

states & statements
Example: C
int f = 1
int x = 5
int s = f + x
while (x > 1) {
f = x * f ;
x = x - 1
}
19
variable
expression

states & statements
Example: C
int f = 1
int x = 5
int s = f + x
while (x > 1) {
f = x * f ;
x = x - 1
}
19
variable
expression
assignment

states & statements
Example: C
int f = 1
int x = 5
int s = f + x
while (x > 1) {
f = x * f ;
x = x - 1
}
19
variable
expression
assignment
control flow

states & statements
Example: Tiger
/* factorial function */
let
var f := 1
var x := 5
var s := f + x
in
while x > 1 do (
f := x * f ;
x := x - 1
)
end
20

states & statements
Example: Tiger
let
var f := 1
var x := 5
var s := f + x
in
while x > 1 do (
f := x * f ;
x := x - 1
)
end
20
variable

states & statements
Example: Tiger
let
var f := 1
var x := 5
var s := f + x
in
while x > 1 do (
f := x * f ;
x := x - 1
)
end
20
variable
expression

states & statements
Example: Tiger
let
var f := 1
var x := 5
var s := f + x
in
while x > 1 do (
f := x * f ;
x := x - 1
)
end
20
variable
expression
assignment

states & statements
Example: Tiger
let
var f := 1
var x := 5
var s := f + x
in
while x > 1 do (
f := x * f ;
x := x - 1
)
end
20
variable
expression
assignment
control flow

procedures

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
22
modularity

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
pass parameter
22
modularity

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
pass parameter
22
new stack frame
modularity

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
pass parameter
22
access parameter
new stack frame
modularity

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
pass parameter
22
access parameter
new stack frame
modularity
old stack frame

push 21
push 42
call _f
add SP 8
push BP
mov BP SP
mov AX [BP + 8]
mov DX [BP + 12]
add AX DX
pop BP
ret
pass parameter
22
access parameter
new stack frame
modularity
old stack frame
free parameters

procedures
Example: C
#include <stio.h>
int fac( int num ) {
if (num < 1)
return 1;
else
return num * fac(num - 1) ;
}
int main() {
int x = 10 ;
int f = fac( x ) ;
int x printf(“%d! = %dn”, x, f);
return 0;
}
23

procedures
Example: C
#include <stio.h>
if (num < 1)
return 1;
else
}
int main() {
int x = 10 ;
int f = fac( x ) ;
return 0;
}
23
formal parameter

procedures
Example: C
#include <stio.h>
if (num < 1)
return 1;
else
}
int main() {
int x = 10 ;
int f = fac( x ) ;
return 0;
}
23
formal parameter
actual parameter

procedures
Example: C
#include <stio.h>
if (num < 1)
return 1;
else
}
int main() {
int x = 10 ;
int f = fac( x ) ;
return 0;
}
23
formal parameter
actual parameter
local variable

procedures
Example: C
#include <stio.h>
if (num < 1)
return 1;
else
}
int main() {
int x = 10 ;
int f = fac( x ) ;
return 0;
}
23
formal parameter
actual parameter
local variable
recursive call

procedures
Example: Tiger
let
function fac( n: int ) : int =
let
var f := 1
in
if n < 1 then
f := 1
else
f := (n * fac(n - 1) );
f
end
var f := 0
var x := 5
in
f := fac( x )
end
24

procedures
Example: Tiger
let
let
var f := 1
in
if n < 1 then
f := 1
else
f := (n * fac(n - 1) );
f
end
var f := 0
var x := 5
in
f := fac( x )
end
24
formal parameter

procedures
Example: Tiger
let
let
var f := 1
in
if n < 1 then
f := 1
else
f := (n * fac(n - 1) );
f
end
var f := 0
var x := 5
in
f := fac( x )
end
24
formal parameter
actual parameter

procedures
Example: Tiger
let
let
var f := 1
in
if n < 1 then
f := 1
else
f := (n * fac(n - 1) );
f
end
var f := 0
var x := 5
in
f := fac( x )
end
24
formal parameter
actual parameter
local variable

procedures
Example: Tiger
let
let
var f := 1
in
if n < 1 then
f := 1
else
f := (n * fac(n - 1) );
f
end
var f := 0
var x := 5
in
f := fac( x )
end
24
formal parameter
actual parameter
local variable
recursive call

call by value vs. call by reference
Example: Tiger
let
type vector = array of int
function init(v: vector) =
v := vector[5] of 0
function upto(v: vector, l: int) =
for i := 0 to l do
v[i] := i
var v : vector := vector[5] of 1
in
init(v) ;
upto(v, 5)
end
25

types

Subtitle Text
Types & Type Checking
Type
• type is category of values
• operation can be applied to all values in some category
Type checking
• safety: ensure that operation is applied to right input values
• static: check during compile time
• dynamic: check during execution
27

dynamic & static typing
Type Systems
Machine code
• memory: no type information
• instructions: assume values of certain types
28

Type Systems
Machine code
Dynamically typed languages
• typed values
• run-time checking & run-time errors
28

Type Systems
Machine code
Dynamically typed languages
• typed values
• run-time checking & run-time errors
Statically typed languages
• typed expressions
• compile-time checking & compile-time errors
28

compatibility
Type Systems
Type compatibility
• value/expression: actual type
• context: expected type
29

compatibility
Type Systems
Type compatibility
Type equivalence
• structural type systems
• nominal type systems
29

compatibility
Type Systems
Type compatibility
Type equivalence
• structural type systems
• nominal type systems
Subtyping
• relation between types
• value/expression: multiple types
29

type compatibility
Example: Tiger
let
type A = int
type B = int
type V = array of A
type W = V
type X = array of A
type Y = array of B
var a: A := 42
var b: B := a
var v: V := V[42] of b
var w: W := v
var x: X := w
var y: Y := x
in
y
end
30

record types
Type Systems
Record
• consecutively stored values
• fields accessible via different offsets
Record type
• fields by name, type, position in record
• structural subtyping: width vs. depth
31
type R1 = {f1 : int, f2 : int}
type R2 = {f1 : int, f2 : int, f3 : int}
type R3 = {f1 : byte, f2 : byte}

biology
Polymorphism
32

biology
Polymorphism
32
the occurrence of more than one form

biology
Polymorphism
33

biology
Polymorphism
34
can give blood to can give plasma to

programming languages
Polymorphism
35

Polymorphism
21 + 21
35

Polymorphism
21 + 21
21.0 + 21.0
35

Polymorphism
21 + 21
21.0 + 21.0
"foo" + "bar"
35

Polymorphism
print(42)
print(42.0)
print("foo")
36

Polymorphism
21 + 21
21.0 + 21.0
21 + 21.0
21 + "bar"
37

polymorphism
Type Systems
Ad-hoc polymorphism
overloading
• same name, different types, same operation
• same name, different types, different operations
type coercion
• implicit conversion
Universal polymorphism
subtype polymorphism
• substitution principle
parametric polymorphism
38
21 + 21
21.0 + 21.0
print(42)
print(42.0)
"foo" + "bar"
21 + "bar"

objects & messages

objects & messages
Modularity
Objects
• generalization of records
• identity
• state
• behavior
40

objects & messages
Modularity
Objects
• generalization of records
• identity
• state
• behavior
Messages
• objects send and receive messages
• trigger behavior
• imperative realization: method calls
40

types

classes
Modularity
Classes
• generalization of record types
• characteristics of objects: attributes, fields, properties
• behavior of objects: methods, operations, features
42
public class C {
public int f1;
private int f2;
public void m1() { return; }
private C m2(C c) { return c; }
}

classes
Modularity
Classes
• generalization of record types
• characteristics of objects: attributes, fields, properties
• behavior of objects: methods, operations, features
Encapsulation
• interface exposure
• hide attributes & methods
• hide implementation
42
public class C {
public int f1;
private int f2;
public void m1() { return; }
private C m2(C c) { return c; }
}

inheritance vs. interfaces
Modularity
Inheritance
• inherit attributes & methods
• additional attributes & methods
• override behavior
• nominal subtyping
43
public class C {
public int f1;
public void m1() {…}
}
public class D extends C {
public int f2;
}
public interface I {
public int f;
public void m();
}
public class E implements I {
public int f;
public void m() {…}
public void m’() {…}
}

inheritance vs. interfaces
Modularity
Inheritance
• inherit attributes & methods
• additional attributes & methods
• override behavior
Interfaces
• avoid multiple inheritance
• interface: contract for attributes & methods
• class: provides attributes & methods
43
public class C {
public int f1;
}
public class D extends C {
public int f2;
}
public interface I {
public int f;
public void m();
}
public class E implements I {
public int f;
public void m() {…}
public void m’() {…}
}

polymorphism
Type Systems
44

polymorphism
Type Systems
Ad-hoc polymorphism
overloading
• same method name, independent classes
• same method name, same class, different parameter types
overriding
• same method name, subclass, compatible types
44

polymorphism
Type Systems
Ad-hoc polymorphism
overloading
• same method name, independent classes
• same method name, same class, different parameter types
overriding
• same method name, subclass, compatible types
Universal polymorphism
subtype polymorphism
• inheritance, interfaces
parametric polymorphism
44

static vs. dynamic dispatch
Type Systems
Dispatch
• link method call to method
45

Type Systems
Dispatch
Static dispatch
• type information at compile-time
45

Type Systems
Dispatch
Static dispatch
• type information at compile-time
Dynamic dispatch
• type information at run-time
• single dispatch: one parameter
• multiple dispatch: more parameters
45

single dispatch
Example: Java
public class A {} public class B extends A {} public class C extends B {}
public class D {
public A m(A a) { System.out.println("D.m(A a)"); return a; }
public A m(B b) { System.out.println("D.m(B b)"); return b; }
}
public class E extends D {
public A m(A a) { System.out.println("E.m(A a)"); return a; }
public B m(B b) { System.out.println("E.m(B b)"); return b; }
}
46
A a = new A(); B b = new B(); C c = new C(); D d = new D(); E e = new E();
A ab = b; A ac = c; D de = e;
d. m(a); d. m(b); d. m(ab); d. m(c); d. m(ac);
e. m(a); e. m(b); e. m(ab); e. m(c); e. m(ac);
de.m(a); de.m(b); de.m(ab); de.m(c); de.m(ac);

overloading vs. overriding
Example: Java
public class F {
public A m(B b) { System.out.println("F.m(B b)"); return b; }
}
public class G extends F {
public A m(A a) { System.out.println("G.m(A a)"); return a; }
}
public class H extends G {
public B m(B b) { System.out.println("H.m(B b)"); return b; }
}
47
A a = new A(); B b = new B(); F f = new F(); G g = new G(); H h = new H();
A ab = b;
f.m(b);
g.m(a); g.m(b); g.m(ab);
h.m(a); h.m(b); h.m(ab);

Except where otherwise noted, this work is licensed under

copyrights
Pictures
Slide 1: Popular C++ by Itkovian, some rights reserved
Slide 4: PICOL icons by Melih Bilgil, some rights reserved
Slides 7, 9, 13: Dual Processor Module by roobarb!, some rights reserved
Slides 11, 14: The C Programming Language by Bill Bradford, some rights reserved
Slides 12, 15, 16, 19: Tiger by Bernard Landgraf, some rights reserved
Slide 21: Adam and Eva by Albrecht Dürer, public domain
Slide 22: ABO blood type by InvictaHOG, public domain
Slide 23: Blood Compability and Plasma donation compatibility path by InvictaHOG, public domain
Slide 28: Delice de France by Dominica Williamson, some rights reserved
Slide 46: Nieuwe Kerk by Arne Kuilman, some rights reserved
49

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