cse305 – programming languages recitation february 11...
TRANSCRIPT
CSE305 – Programming LanguagesRecitation February 11, 2010
Dan Schlegel“Should array indices start at 0 or 1? My
compromise of 0.5 was rejected without, I thought, proper consideration.”
(Stan Kelly-Bootle, Author, musician and recipient of the first postgraduate degree in CS)
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HW4 Concerns?
http://www.cse.buffalo.edu/~shapiro/Courses/CSE305/2010/Homeworks/hw4.pdf
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Common problems with past homework
HW2 #1:(3) Write any <if statement> that is legal according to the following grammar:<statement> -> <if statement> | <assignment statement><if statement> -> if <expr> then <statement> else <statement> endif ;<assignment statement> -> <id> := <expr> ;<expr> -> <id><id> -> i | j | k | x | y | z
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Common problems with past homework
HW2 #2(3) Write a varid that is legal according to the Haskell grammar
presented athttp://haskell.org/onlinereport/lexemes.htmlYour varid must have at least 6 characters, no two of which are the
same.
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Common problems with past homework
HW3 #4(3) Assume that f1 and f2 in the following Ruby program each use m bytes of stack memory for its
local storage. What is the maximum amount of total stack memory ever used by f1 and f2 during the run of the program?
def f1(n)puts "In f1(#{n})."if n == 0
returnelsif n == 1
f2(3)endf1(n-1)end
def f2(m)puts "In f2(#{m})."
end
f1(2)
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Common problems with past homework
Of general concern:• Pay attention to the websites you are using!• Read the directions, do the problem, re-read
the directions!
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Review for MidtermA 10 Minute “Quiz”
1. Define Static Scope2. Define Dynamic Scope3. What variables are visible during the
execution of the last subprogram called? (Use the Ada program to the right). Assume dynamic scoping.
Main calls Sub3 calls Sub2 calls Sub14. What are the advantages and
disadvantages of an implicitly typed language?
5. How is static type checking better than dynamic?
6. In EBNF construct a grammar for the for loop statement in Java (be as detailed as you can within the time constraints – do this last).
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
*#3 is part (f) of #12 on p445 in Sebesta
Quiz Solutions
• Dynamic Scope:
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Quiz Solutions
• Dynamic Scope: Scoping based on the calling sequence of the subprograms.
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Quiz Solutions
• Dynamic Scope: Scoping based on the calling sequence of the subprograms.
• Static Scope:
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Quiz Solutions
• Dynamic Scope: Scoping based on the calling sequence of the subprograms.
• Static Scope: Scoping based on the spatial relationship of the subprograms.
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Quiz Solutions
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
What variables are visible during the execution of the last subprogram called?
Main calls Sub3 calls Sub2 calls Sub1
Quiz Solutions
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
Main: X, Y, Z
Visible: Main: X, Y, Z
What variables are visible during the execution of the last subprogram called?
Main calls Sub3 calls Sub2 calls Sub1
Quiz Solutions
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
Main: X, Y, Z
Visible: Main: Y, Z; Sub3: A, X, W
Sub3: A, X, W
What variables are visible during the execution of the last subprogram called?
Main calls Sub3 calls Sub2 calls Sub1
Quiz Solutions
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
Main: X, Y, Z
Visible: Main: Y; Sub3: X, W; Sub2: A, B, Z
Sub3: A, X, W
Sub2: A, B, Z
What variables are visible during the execution of the last subprogram called?
Main calls Sub3 calls Sub2 calls Sub1
Quiz Solutions
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procedure Main is X, Y, Z : Integerprocedure Sub1 is
A, Y, Z : Integer;begin…end;
procedure Sub2 isA, B, Z : Integer;begin…end;
procedure Sub3 isA, X, W : Integer;begin…end;
begin…end;
Main: X, Y, Z
Visible: Sub3: W; Sub2: B; Sub1: A, Y, Z
Sub3: A, X, W
Sub2: A, B, Z
Sub1: A, Y, Z
What variables are visible during the execution of the last subprogram called?
Main calls Sub3 calls Sub2 calls Sub1
Quiz Solutions
• Advantages / Disadvantages of Implicit Typing
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Quiz Solutions
• Advantages / Disadvantages of Implicit Typing– A: Maintains some type safety– A: Programming is easier/faster– D: It can become harder to understand/read code– Note: Generally used in functional languages, but
C#3.0+ supports it as well.
• How is static typing better than dynamic
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Quiz Solutions
• Advantages / Disadvantages of Implicit Typing– A: Maintains some type safety– A: Programming is easier/faster– D: It can become harder to understand/read code– Note: Generally used in functional languages, but
C#3.0+ supports it as well.
• How is static typing better than dynamic– Type safety at compile time!
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Java For Loop
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Java For Loop
• for_statement ::= "for" "(" ( variable_declaration | ( expression ";" ) | ";" ) [ expression ] ";" [ expression ] ";" ")"statement
21http://www.daimi.au.dk/dRegAut/JavaBNF.html