Exam 2 u Wednesday, November 4 u Topics: u Names, types, semantics, - - PDF document
11/1/15 CSCI 2325 Principles of Programming Languages Semantics Reading: Ch 7 (Tucker & Noonan) Exam 2 u Wednesday, November 4 u Topics: u Names, types, semantics, memory management, and function (up to Mondays lecture) u
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u Wednesday, November 4 u Topics:
u Names, types, semantics, memory management,
and function (up to Monday’s lecture)
u Must read book chapters 4, 5, 7, 11, and 9 and go
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u Given a program, what will be the output if static scoping is
used? what will be its output if dynamic scoping is used? (Ch 4)
u Difference between lifetime and scope. Give example. (Ch
4)
u Static vs. dynamic typing – what is the difference? (Ch 5) u What does a strongly typed language mean? (Ch 5) u How are arrays implemented? Extend 1-dimensional array
shown in class to 2-dimensional array. (Ch 5)
u Are functions types? Give examples. (Ch 5) u Given a statement, give a verbal description of its
u Simulate the three memory management algorithms on a
given example. (Ch 11)
u Given a recursive function, draw the activities in the run-
time stack when the function is called. (Ch 9.7)
u Other questions from the topics covered during the classes.
1.
2.
3.
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u The meaning attached by compiling using compiler
C and executing using machine M. Ex: Fortran on IBM 709.
u Use mathematical logic
u Use mathematical functions u These functions transform the “state” of the
program u We’ll use the concept of denotational
u Infix (C, Java): a + b - c * d
u Ambiguous without rules of prec. & assoc.
u Polish Prefix (Ambi): - + a b * c d
u Unambiguous! u But cannot use – as both unary and binary
u Polish Postfix (Postscript, calculator):
u Cambridge Polish (LISP, Scheme):
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u Semantics of: a < b < c in C/C++?
u if (a < b) return 1 < c; else return 0 < c;
u Why did Ada make relational operators non-
u To make a < b < c illegal
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u a and b evaluated as:
u if a then b else false
u a or b evaluated as:
u if a then true else b
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u Is the meaning of
u No! u There are considerations beyond just
u Hardware representation of numbers
u What is the value of a below?
u Here, the semantics of the RHS expression
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u Allow multiple assignments?
u a = b = c = 0 u OK by C/C++/Java/Python
u Is assignment an expression?
u Why do I ask? If it’s an expression, you can use
assignment as a conditional expression!
u C
u //Kernighan and Ritchie’s strcpy function
while (*p++ = *q++) ;
u while (ch = getc(fp)) ... // ??? u while (p = p->next) ... // ???
u Java boolean x = false; if (x = true) System.out.println("x is true!"); //this will be printed! u Python
u These are illegal
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u x = y
u Program state
u collection of all active objects and their current
values (binding!)
11/1/15 9 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f undef undef undef 3 undef undef
11/1/15 10 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 undef undef 3 1 undef // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 1 undef 3 1 1
11/1/15 11 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 1 1 3 1 1 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 1 1 3 2 1
11/1/15 12 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 2 1 3 2 2 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f … …
11/1/15 13 // compute n! 1 void main ( ) { 2 int n, i, f; 3 n = 3; 4 i = 1; 5 f = 1; 6 while (i < n) { 7 i = i + 1; 8 f = f * i; 9 } 10 } n i f 3 3 6
u To be complete, an imperative language
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u s1
u Semantics:
u First execute s1 u Then execute s2 u Output state of s1 is the input state of s2
u IfStatement → if ( Expresion ) Statement u
u Example: u if (a > b) u z = a; u else u z = b;
u If the test expression is
true (here, no change
u then the output state
the output state of the then branch,
u else the output state of
the conditional is the
branch.
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u WhileStatement → while (Expr) Statement u The expression is evaluated (state does not
u If it is true, first the statement is executed, u and then the loop is executed again. u Otherwise the loop terminates.
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u Hardware– Interrupt
u Your program: division by 0/illegal memory addr à
Interrupt handler routine in HW à Back to the next line of your program
u Only one interrupt handler routine for div by 0 u Resumption model
u Programming Lang. – Exception
u Your program: array index out of bound/access
Corresponding exception handler à Back to a specific part of your program
u You can have multiple exception handlers for the
same exception
u Termination model
u COBOL à PL/I à Ada à C++/Java… u No exception handling: Fortran/Pascal/C
u Programmer’s responsibility
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try { //throw 20; //throw “Some error”; } catch(int a) { //This kicks in if an int is thrown. } catch(char* st) { //This kicks in if a string is thrown. }
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u Code by Jakob Jenkov
try { // execute code that may throw // 1 of the 3 exceptions below. } catch(SQLException e) { logger.log(e); } catch(IOException e) { logger.log(e); } catch(Exception e) { logger.severe(e); }
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