Programming Languages Implementation of Control Structures

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Programming Languages Implementation of Control Structures

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Title: Programming Languages Implementation of Control Structures

1
Programming Languages Implementation of Control
Structures

Cao Hoaøng Truï
Khoa Coâng Ngheä Thoâng Tin
Ñaïi Hoïc Baùch Khoa TP. HCM

2
Contents

Sequence control
Data control

3
Sequence Control

Expressions
Statements
Subprograms

4
Expressions

Control mechanism
Syntax
Execution-time representation
Evaluation

5
Control Mechanism

Functional composition
(A B)(C - A)
( (A, B), - (C, A))

6
Syntax

Infix
A B C
binary operations only
computation order ambiguity

7
Syntax

Prefix
ordinary
( (A, B), - (C, A))
Cambridge Polish
( ( A B) (- C A))
Polish
A B - C A

8
Syntax

Prefix
different numbers of operands
ordinary/ Cambridge Polish cumbersome with
parentheses
Polish number of operands known in advance

9
Syntax

Postfix
ordinary
((A, B) , (C, A) -)
Polish
A B C A -
suitable execution-time representation

10
Execution-Time Representation

Interpretation
tree structures

-
A
B
C
A

prefix or postfix

11
Execution-Time Representation

Compilation machine code sequences
PUSH A
PUSH B
ADD
PUSH C
PUSH A
SUB
MUL

A
A
A B
B
A B
A B
A B
(AB)(C-A)
C
C
C - A
A
12
Execution-Time Representation

Compilation machine code sequences
PUSH A
PUSH B
ADD
PUSH C
PUSH A
SUB
MUL

A
A
A B
B
A B C A -
A B
A B
A B
(AB)(C-A)
C
C
C - A
A
13
Evaluation

No simple uniform evaluation rule is
satisfactory

-
A
B
C
A
14
Evaluation

Side effects
A FOO(X) A

A
A
FOO(X)
15
Evaluation

Side effects
A B C 1020 10-20 10-20
(A B) C 1 10-20 10-20
A (B C) 1020 0 0

16
Evaluation

Short-circuit Boolean expressions
if (A 0) or (B/A gt C) then

17
Evaluation

Short-circuit Boolean expressions
if (A 0) or else (B/A gt C) then

18
Sequence Control

Expressions
Statements
Subprograms

19
Statements

GOTO
Sequencing
Selection
Iteration

20
GOTO

GOTO L

JMP L
L
21
Sequencing

begin
S1
S2
Sn
end

S1 codes
S2 codes
Sn codes
22
Selection

if A 0 then S1
else S2
S3

JEQ0 A L1
S2 codes
JMP L2
S1 codes
L1
S3 codes
L2
23
Selection
E ? v

case

var E 0..2
case E of
1 S1
2 S2
else S0
end
S3

JMP av
a
JMP L0
a1
JUMP table
JMP L1
a2
JMP L2
L1
S1 codes
JMP L3
L2
S2 codes
JMP L3
L0
S0 codes
L3
S3 codes
24
Iteration

for I E1 to E2 do S
I E1
L0 if I gt E2 then GOTO L1
S
I I 1
GOTO L0
L1

25
Iteration

while

while C do S
L0 if not(C) then GOTO L1
S
GOTO L0
L1

26
Iteration

repeat

repeat S until C
L0 S
if not(C) then GOTO L0

27
Sequence Control

Expressions
Statements
Subprograms

28
Subprograms

Simple call-return
Recursive calls

29
Simple Call-Return

No recursive calls
Explicit calls
Complete execution
Immediate control transfer
Single execution sequence

30
Simple Call-Return
MAIN
A
B
I0
I2
I4
call A
call B
I1
I3
return
return
end
31
Simple Call-Return
MAIN
I0
call A
I1
end
local data MAIN
CIP (current instruction pointer)
I0
32
Simple Call-Return
MAIN
A
I0
I2
call A
call B
I1
I3
return
end
local data A
local data MAIN
I1
I2
CIP
33
Simple Call-Return
MAIN
A
B
I0
I2
I4
call A
call B
I1
I3
return
return
end
local data B
local data A
local data MAIN
I3
I1
I4
CIP
34
Recursive Calls
MAIN
A
B
I0
I2
I4
call A
call B
call A
I1
I3
I5
end
return
return
R0
--
--
local data MAIN
CEP (current environment pointer)
I0
CIP
R0
35
Recursive Calls
MAIN
A
B
I0
I2
I4
call A
call B
call A
I1
I3
I5
end
return
return
R0
R1
--
I1
--
R0
local data MAIN
local data A
I2
CIP
R1
CEP
36
Recursive Calls
MAIN
A
B
I0
I2
I4
call A
call B
call A
I1
I3
I5
end
return
return
R0
R1
R2
--
I1
I3
--
R0
R1
local data MAIN
local data A
local data B
I4
CIP
R2
CEP
37
Recursive Calls
MAIN
A
B
I0
I2
I4
call A
call B
call A
I1
I3
I5
end
return
return
R0
R1
R2
R3
--
I1
I3
I5
--
R0
R1
R2
local data MAIN
local data A
local data B
local data A
I2
CIP
R3
CEP
38
Recursive Calls
MAIN
A
B
I0
I2
I4
call A
call B
call A
I1
I3
I5
end
return
return
R0
R1
R2
R3
--
I1
I3
I5
--
R0
R1
R2
local data MAIN
local data A
local data B
local data A
Dynamic chain
I2
CIP
R3
CEP
39
Central Stack
MAIN
R0
I0
--
I0
CIP
--
MAIN
call A
R0
CEP
local data
I1
end
40
Central Stack
MAIN
R0
I0
--
I2
CIP
--
MAIN
call A
R1
CEP
local data
I1
R1
I1
end
R0
A
A
local data
I2
call B
I3
return
41
Central Stack
A
R0
I2
--
I4
CIP
--
MAIN
call B
R2
CEP
local data
I3
R1
I1
return
R0
A
B
local data
R2
I4
I3
R1
B
call A
local data
I5
return
42
Central Stack
B
R0
--
I4
I2
CIP
--
MAIN
call A
local data
R3
CEP
I5
R1
I1
return
R0
A
local data
A
R2
I3
I2
R1
B
local data
call B
R2
I3
I5
return
R2
A
local data
43
Exercises

Illustrate the storage representation of
A array 0..1, 1..2, 1..3 of integer using the
column-major order.
Give the accessing formula for computing the
location of AI, J, K, supposing that the size
of an integer is 2 bytes.

44
Exercises

Given the following program
program MAIN
function FAC(N integer) integer
begin if N lt 1
then FAC 1
else FAC N FAC(N - 1)
end
begin
write(FAC(3))
end.
Illustrate the code segment and activation
records of MAIN and FAC in the central stack
during execution of the program.

45
Contents

Sequence control
Data control

46
Data Control

Basic concepts
Local data and environments
Shared data dynamic scope
Shared data block structure
Shared data parameter transmission

47
Basic Concepts

Names
Referencing environments
Scope
Block structure

48
Names

Variable names
Formal parameter names
Subprogram names
Names for defined types
Names for defined constants

49
Referencing Environments

Association
Name --------gt Data Object
Referencing environment set of associations

50
Referencing Environments

program MAIN
var X integer
X 0

object
Association
51
Referencing Environments

Local
Non-Local
Global
Predefined

52
Local Environments

program MAIN
var X integer
procedure SUB1
var X real
X 1

object1
object2
53
Non-Local Environments

program MAIN
var X integer
procedure SUB1
var X real
procedure SUB2
X 2

object1
object2
54
Global Environments

program MAIN
var X integer
procedure SUB1
var X real
procedure SUB3
X 3

object1
object2
55
Predefined Environments

program MAIN
var X integer
X MAXINT - 1
write(X)

65535
codes for write
56
Referencing Environments

Visibility of an association
Referencing operations
Local, non-local, global references

57
Visibility

program MAIN
var X integer
procedure SUB1
var X real
X 1

Hidden
object1
Visible
object2
58
Referencing Operations

Name ? Environment ? Data Object

59
Referencing Operations

program MAIN
var X integer
procedure SUB1
var X real
X 1

object1
object2
X ? (X ? object2) ? object2
60
Referencing Environments

Visibility of an association
Referencing operations
Local, non-local, global references

61
Local References

program MAIN
var X integer
procedure SUB1
var X real
X 1

object1
object2
X ? (X ? object2) ? object2
62
Non-Local References

program MAIN
var X integer
procedure SUB1
var X real
procedure SUB3
X 2

object1
object2
X ? (X ? object2) ? object2
63
Global References

program MAIN
var X integer
procedure SUB1
var X real
procedure SUB2
X 2

object1
object2
X ? (X ? object1) ? object1
64
Basic Concepts

Names
Referencing environments
Scope
Block structure

65
Scope

The program part (text or execution) within which
the binding is effective.

66
Dynamic Scope

The subprogram activations within which the
association is effective.

67
Dynamic Scope

program MAIN
var X integer
procedure SUB1
var X real
X 1
procedure SUB2
X 2

MAIN
SUB2
object1
SUB1
68
Static Scope

The program text within which the declaration is
effective.

69
Static Scope

program MAIN
var X integer X ? integer
procedure SUB1
var X real
X 1
procedure SUB2
X 2

70
Static Scope

program MAIN
var X integer X ? integer
procedure SUB1
var X real
X 1
procedure SUB2
X 2

Static scopes define dynamic scopes
71
Static Referencing Environments

Local, non-local, global environments
Local, non-local, global references

72
Basic Concepts

Names
Referencing environments
Scope
Block structure

73
Block Structure

program MAIN
procedure SUB1
procedure SUB3
procedure SUB4
procedure SUB2

MAIN
SUB1
SUB3
SUB4
SUB2
74
Static Scope Rules

The declarations
at the head of each
block defines the
local referencing
environment for
that block

MAIN
SUB1
SUB3
X real
SUB4
SUB2
75
Static Scope Rules

2. If no local declarations
exists, then refer to the
nearest enclosing block
having the declaration
in need

MAIN
X integer
SUB1
X real
SUB3
X 1
SUB4
SUB2
76
Static Scope Rules

3. Any local declaration
of a block is hidden
from its outer blocks

MAIN
SUB1
X real
SUB3
SUB4
SUB2
77
Static Scope Rules

4. The block name is
part of the local
referencing environment
of the containing block

MAIN
SUB1
SUB3
SUB4
SUB2
78
Data Control

Basic concepts
Local data and environments
Shared data dynamic scope
Shared data block structure
Shared data parameter transmission

79
Local Data and Environments

procedure SUB(X integer)
var Y real
Z array 1..3 of real
procedure SUB1
begin
end
begin
end

SUB
object2
X
object2
Y
object2
Z
SUB1
SUB1 code segment
80
Data Control

Basic concepts
Local data and environments
Shared data dynamic scope
Shared data block structure
Shared data parameter transmission

81
Shared Data Dynamic Scope

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

MAIN
SUB1
SUB2
SUB3
82
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Return point
X
SUB1
Y
83
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Return point
X
SUB1
Dynamic chain
Y
Return point
B
A
SUB2
U
X
84
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Return point
X
SUB1
Y
Dynamic chain
Return point
B
A
SUB2
U
X
Return point
Z
Y
SUB3
A
W
V
85
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Return point
X
SUB1
Y
Dynamic chain
Return point
B
A
SUB2
U
X
Return point
Z
Y
SUB3
A
W
V
86
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Central table
Return point
X
SUB1
A
0
Y
B
0
U
0
V
0
W
0
X
1
Y
1
Z
0
87
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Central table
Return point
X
SUB1
A
1
Y
B
1
Return point
U
1
B
V
0
A
SUB2
W
0
U
X
1
X
Y
1
Z
0
88
Shared Data Dynamic Scope
MAIN

program MAIN
procedure SUB1
var X, Y real
procedure SUB2
var B, A, U, X integer
procedure SUB3
var Z, Y, A, W, V char

Central table
Return point
X
SUB1
1
A
Y
1
B
Return point
1
U
B
1
V
A
SUB2
1
W
U
1
X
X
1
Y
Return point
1
Z
Z
Y
SUB3
A
W
V
89
Shared Data Dynamic Scope
MAIN
Central table
Hidden stack
Return point
X
SUB1
0
A
Y
0
B
0
U
0
V
0
W
1
X
1
Y
0
Z
90
Shared Data Dynamic Scope
MAIN
Central table
Hidden stack
Return point
SUB1
X
1
X
A
Y
1
1
B
Return point
1
1
U
B
0
1
V
A
SUB2
0
1
W
U
0
0
X
X
0
0
Y
0
0
Z
91
Shared Data Dynamic Scope
MAIN
Central table
Hidden stack
Return point
SUB1
X
1
X
A
Y
1
1
B
Y
Return point
1
1
U
1
A
B
0
1
V
A
SUB2
0
1
W
U
0
0
X
X
0
0
Y
0
0
Z
Return point
Z
Y
SUB3
A
W
V
92
Data Control

Basic concepts
Local data and environments
Shared data dynamic scope
Shared data block structure
Shared data parameter transmission

93
Shared Data Block Structure

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

MAIN X, Y, Z char
SUB2 X, Y integer
SUB3 X real
SUB4
SUB1 Y, Z integer
94
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
1
1
0
0
0
0
0
0
? MAIN
95
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
1
1
Y
0
0
0
0
0
? SUB2
96
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
1
1
Y
0
1
X
0
0
0
0
? SUB3
97
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
1
1
Y
0
1
X
0
0
0
0
? SUB4
98
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
1
1
Y
0
1
X
0
0
0
0
SUB4 ?
99
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
1
1
Y
0
1
X
0
0
0
0
SUB3 ?
100
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
1
0
1
X
0
0
0
0
SUB2 ?
101
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
X
Y
1
Z
0
1
X
0
0
0
0
? SUB1
102
Block Structure Compile Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

Symbol table
Scope stack
X
1
Y
1
1
1
Z
1
1
0
1
X
0
0
0
0
SUB1 ?
103
Block Structure Run Time

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

MAIN
SUB1
SUB2
SUB3
104
Block Structure Run Time
--

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

X
MAIN
Y
Z
105
Block Structure Run Time
--

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

X
MAIN
Static chains
Y
Z
RP
SCP
SUB1
Y
Z
106
Block Structure Run Time
--

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

X
MAIN
Y
Z
Static chains
RP
SCP
SUB1
Y
Z
RP
SCP
SUB2
X
Y
107
Block Structure Run Time
--

program MAIN
var X, Y, Z char
procedure SUB2
var X, Y integer
procedure SUB3
var X real
procedure SUB4
procedure SUB1
var Y, Z integer

X
MAIN
Y
Z
Static chains
RP
SCP
SUB1
Y
Z
RP
SCP
SUB2
X
Y
RP
SUB3
SCP
X
108
Block Structure Run Time
C
C
A
A
A
B
B
B
MAIN
MAIN
MAIN
A
C
C
A
A
B
B
B
109
Block Structure Run Time
--
X
MAIN
Display
Y
Z
0
RP
1
1
SCP
2
SUB1
Active static chain
Y
1
Z
1
RP
SCP
SUB2
X
0
Y
RP
loc Y Display1 offset
SUB3
SCP
X
110
Data Control

Basic concepts
Local data and environments
Shared data dynamic scope
Shared data block structure
Shared data parameter transmission

111
Parameter Transmission

Parameters
formal parameters
actual parameters
Transmission
by reference
by value

112
Parameter Transmission

procedure SUB2(K integer var L integer)
begin
K K 10
L L 10
write(K, L)
end
procedure SUB1
begin
I 1
J 2
SUB2(I, J)
write(I, J)
end

RP
SCP
SUB1
I
1
J
2
RP
SCP
SUB2
K
1
L
113
Parameter Transmission

procedure SUB2(K integer var L integer)
begin
K K 10
L L 10
write(K, L)
end
procedure SUB1
begin
I 1
J 2
SUB2(I, J)
write(I, J)
end

RP
SCP
SUB1
I
1
J
2
RP
SCP
SUB2
K
11
L
114
Parameter Transmission

procedure SUB2(K integer var L integer)
begin
K K 10
L L 10
write(K, L)
end
procedure SUB1
begin
I 1
J 2
SUB2(I, J)
write(I, J)
end

RP
SCP
SUB1
I
1
J
12
RP
SCP
SUB2
K
11
L
115
Parameter Transmission

procedure SUB2(Kinteger var Linteger)
begin
K K 10
L L 10
SUB3(K, L)
write(K, L)
end
procedure SUB1
begin
I 1
J 2
SUB2(I, J)
write(I, J)
end

procedure SUB3(var M, N integer) begin M M
10 N N 10 write(M, N) end
Actual parameters are formal parameters of the
calling program
116
Parameter Transmission

type VECT array 1...3 of integer
procedurre SUB2 (CVECT var DVECT)
var I integer
begin
C 2 C 2 10
D 2 D 2 10
for I 1 to 3 do write (C I)
for I 1 to 3 do write (D I)
end

procedurre SUB1 var A, B VECT J
integer begin A 1 7 A 2 8 A 3
9 B 1 7 B 2 8 B 3 9 SUB2
(A, B) for J 1 to 3 do write (A J) for
J 1 to 3 do write (B J) end
Actual parameters are structured data objects
117
Parameter Transmission

type VECT array 1...3 of integer
procedurre SUB2 (I integer var J integer)
begin
I I 10
J J 10
write (I, J)
end

procedurre SUB1 var A VECT K
integer begin A 1 7 A 2 8 A 3
9 SUB2 (A1, A2) for K 1 to 3 do write
(AK) end
Actual parameters are components of structured
data objects
118
Parameter Transmission

type VECT array 1...3 of integer
procedurre SUB2 (var I, J integer)
begin
I I 1
J J 1
write (I, J)
end

procedurre SUB1 var A VECT K
integer begin A 1 7 A 2 8 A 3
9 K 2 SUB2 (K, AK) for K 1 to 3 do
write (AK) end
Actual parameters are array components with
computed subscripts
119
Parameter Transmission

type VECT array 1...3 of integer
VECTPTR VECT
procedurre SUB2 (RVECTPTR var SVECTPTR)
begin
R1 R1 10
S1 S1 10
if . . . then R S else S R
end

procedurre SUB1 var A, B VECT P, Q
VECTPTR begin A 1 7 A 2 8 A 3
9 B 1 7 B 2 8 B 3 9 P _at_A
Q _at_B SUB2 (P, Q) end
Actual parameters are pointers
120
Parameter Transmission

program MAIN
var X real
procedurre SUB2 (X, Y real
function
F(Ureal) real)
var Z real
begin
Z abs (Y - X)
Z (F(X) F(Y)) Z/2
write (Z)
end
begin
X 3
SUB1
end.

procedurre SUB1 var Y real function
FUNC(Vreal) real begin FUNC XV
Y end begin Y 1 SUB2 (0, 1,
FUNC). end
Actual parameters are subprograms
121
Parameter Transmission

type VECT array 1...3 of integer
procedurre SUB2 (name I, J integer)
begin
I I 1
J J 1
write (I, J)
end

procedurre SUB1 var A VECT K
integer begin A 1 7 A 2 8 A 3
9 K 2 SUB2 (K, AK) for K 1 to 3 do
write (AK) end
Transmissiom by names
122
Formal Parameters and Aliases