CMSI 386: Programming Languages: Homework #4

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1. Give an abstract syntax tree for the following C expression:
(a=3)>=m>=!&4*~6||y%=7^6&p
2. JavaScript’s implicit semicolon insertion is often considered to be poorly designed because the following four
cases aren’t exactly intuitive:
functionf(){
return
{x:5}
}
varb=8
vara=b+b
(4+5).toString(16)
varplace=”mundo”
[“Hola”,”Ciao”].forEach(function(command){
alert(command+”,”+place)
})
varsayHello=function(){
alert(“Hello”)
}
(function(){
alert(“Goodbye”)
}())
What is being illustrated in each of the above? Go, Python, Scala, and Ruby all allow line endings to end
statements and you don’t hear people complaining about them the way they do about JavaScript. Pick one of
these four languages and show why they handle the four “problematic” cases of JavaScript.
3. Give an example of a program in C that would not work correctly if local variables were allocated in static
storage as opposed to the stack. For the purposes of this question, local variables do not include
parameters.
4. Consider the following pseudocode:
varx=100;
functionsetX(n){x=n;}
functionprintX(){console.log(x);}
functionfirst(){setX(1);printX();}
functionsecond(){varx;setX(2);printX();}
setX(0);
first();
printX();
second();
printX();
What does this program print if the language uses static scoping? What does it print with dynamic scoping?
Why?
5. The expression a–f(b)–c*d can produce different values depending on how a compiler decides to order,
or even parallelize operations. Give a small program in the language of your choice (or even one of your own
design) that would produce different values for this expression for different evaluation orders. Please note
that by “different evaluation orders” we do not mean that the compiler can violate the precedence and
associativity rules of the language.
6. Explain the meaning of the following C declarations:
double*a[n];
double(*b)[n];
double(*c[n])();
double(*d())[n];
7. Rewrite the four declarations in the previous problem in Go. Yes, I did say Go.
8. Translate the following expression into (a) postfix and (b) prefix notation, in both cases without using
parentheses:
(-b+sqrt(4×a×c))/(2×a)
Do you need a special symbol for unary negation? Why or why not?
9. Write the interleave function from the previous three assignments in C++, using C-style arrays.
10. Write the interleave function from the previous three assignments in C++, using C++ vectors (from the
Standard Library).