Lecture 6

Question 1

What is a binding?

Answer 1

The relation between a syntactic element (keyword) and its meaning during execution

Question 2

What is binding time?

Answer 2

The time at which the meaning of a syntactic entity is established.

E.g. during language design time (C keyword static), or during programming (C keyword int, because programmer need to specify size).

Compile time (when syntactic elements are linked to external libraries)

Question 3

What is link time bindings?

Answer 3

Meaning is established when code is linked to external libraries

Question 4

What is load time bindings?

Answer 4

Meaning is established when program is loaded into memory

Question 5

What is run-time bindings?

Answer 5

Meaning established when program is executed.

Question 6

What are early binding times?

Answer 6

All binding times up to the load time, inclusive

Question 7

What is late binding times?

Answer 7

Run time bindings (start-up time, module, entry time, elaboration time, procedure call time, etc)

Question 8

How are global values allocated in memory?

Answer 8

Allocated statically, location of object is fixed at load time.

Question 9

How is procedure memory allocated?

Answer 9

On stack, FIFO

Procedure calls sets up a call frame that is allocated on stack.

This includes callers address, local vars, result vars, arguments for further calls.

Question 10

How are the components of OZ layed out in memory?

Answer 10

Semantic stack: corresponds to stack-allocated call frames.

Assignment store: heap

Question 11

What is implicit and explicit memory allocation

Answer 11

Automatic(procedure call/return) and manual(in program) allocation and dealocation

Question 12

What is object and reference lifetime?

Answer 12

Object: Time between allocation and deallocation

reference: Time between creation, in environment, and deletion of mapping

Question 13

What is static and dynamic scoping?

Answer 13

Static (lexical): A textual region of the code

Dynamic: A fragment of proceeding computation

Question 14

When does some garbage collectors remove memory?

Answer 14

When there are no longer references to parts of memory.

Question 15

What is dangling references?

Answer 15

When a pointer to a local variable is returned. This local variable will be deallocated when function returns, leaving the pointer dangling.

Question 16

How does dynamic scoping work?

Answer 16

Identifiers are looked up in the caller’s environment, rather than the environment when the identifier first was created.

Question 17

What is a recursive procedure?

Answer 17

A proc that calls itself within its own body

Question 18

What is a recursive computation?

Answer 18

A recursive procedure is called repetitively so that the result of each calldepends on the result of the subsequent calls

Question 19

What is a property of a recursive computation?

Answer 19

The nested call is not the last statement.

Question 20

What is the difference between iteration and recursion?

Answer 20

In iteration, the stack is kept constant in size.

Recursion:
declare
fun {Factorial N}
if N < 2 then 1
else N * {Factorial N - 1} end
end

Iteration:
declare
fun {Factorial N}
fun {Iterate Iterator Accumulator}
if Iterator >N then Accumulator
else {Iterate Iterator+1 Accumulator*Iterator} end end in
{Iterate 2 1}
end

Question 21

What is tail recursion?

Answer 21

Recursive procedures that specify iterative processes.
Constant stack size.
Recursive call is the last one to be executed within the body.

Question 22

What is last call optimization?

Answer 22

The technique that allows a tail-recursive procedure to return immediately instead of going through stacked callframes.

Question 23

Implement {Length L} recursively and tail-recursively

Answer 23

Recursive:
fun {Length L}
case L of nil then 0
[] H|T then
1 + {Length Tail}
end
end

Iteratively:
fun {Length L}
fun {Iterate L A}
case L of nil then A
[] H|T then {Iterate T A+1}
end
in
{Iterate L 0}
end

Question 24

What is a context?

Answer 24

A semantic statement on the stack

Question 24

What is the syntax for raise and try catch statements?

Answer 24

fun {Func X Y}
…
raise ‘this is an exception’ end
end

try
{Func 1 4}
catch ‘this is an exception’
// handle
end

Question 25

What is the execution rule for a try statement?

Answer 25

try <s1> catch <id> then <s2> end</s2></id></s1>

Push:
catch <id> then <s2> end</s2></id>

push:

<s1>
</s1>

Question 26

What is the semantics of raise?

Answer 26

(raise <id> end, E)</id>

Pop from stack until we find <id> in a catch</id>

Stop with error if stack empty and this is not found

If found, push to stack the statement within the catch (<s2>)
E = Ec + {<id> -> E(<id>)}</id></id></s2>

Question 27

What is an n+1 order procedure?

Answer 27

At least 1 argument is an n-order procedure

Question 28

What is procedural abstraction?

Answer 28

Converting statement into procedure

Question 29

What is Instantiation?

Answer 29

Producing procedures by calling procedure-generating procedures with appropriate arguments

Question 30

What is genericity?

Answer 30

Abstracting out part of the procedure body into an argument

Question 31

What is embedding?

Answer 31

Including procedures in data structures.

Question 33

Create a generic Map function

Answer 33

{Map List Op}
case List of nil then nil
[] H|T then {Op H} | {Map T Op}
end

Question 34

What is right- and left folding?

Answer 34

Folds a list in a right-associative manner.
(1+(2+(3+(4+0)))

Left:
((((1+2)+3)+4)+0)

Question 35

Create a generic rightfold function

Answer 35

fun {Rightfold List Op Combine}
case List of nil then nil
[] H|T then
{Combine {Op H} {Rightfold T Op Combine}}
end
end

Question 36

Create a Map function using rightfold

Answer 36

fun {Map List Op}
{Rightfold List Op fun {$ Head Tail} Head|Tail}
end