Week7 ACTUAL

Question 1

What is functional programs and what does it consist of

Answer 1

program that consists of functions and focuses on what is to be computed not how it is computed

Question 2

What is a function

Answer 2

mapping from set A to set B where A is domain and B is codomain

Question 3

Advantages of function programs

Answer 3

.shorter programs
.easier to understand
.easier to design

Question 4

Disadvantage

Answer 4

.Slower than imperative
. Less Flexible

Question 5

Evaluation

Answer 5

Sequence of simplifying an expression (through reduction steps) until a value is obtained that cant be simplified further

Question 6

Properties of evaluation

Answer 6

Unicity :
Value uniquely determined by components of expression and independent of the order of reduction

(ie all terminating reduction sequences must have the same value)

Non terminating:
Not all reduction sequences have a value , some may fail to terminate

Question 7

What are the 2 main strategies of evaluation and explain them

Answer 7

Call by name:
reduce the function using its definition before evaluating its arguments

Call by value:
Evaluate arguments before reducing the function using its definition

Question 8

Lazy evaluation

Answer 8

Haskell’s lazy evaluation is an implementation
of a call by name strategy, where arguments are evaluated if needed, using sharing to avoid
duplicating computations

Question 9

Compare Call by name and call by value

Answer 9

. Call by name -> guaranteed to find a value if there is one
. call by value -> more effient but may fail to find a value even if there is one

Question 10

Advantages of call by value

Answer 10

Advantages:
Since we evaluate arguments first (before reducing the function according to its defintion) no redundant computational steps [ ONLY MORE EFFICIENT IF ARGUMENT IS USED MORE THAN ONCE OTHERWISE EFFICIENCY IS THE SAME]

. easy to implement

Disadvantages:
may fail to find a value ( lead to you not terminating) even if there is a normal form associated to expression

Question 11

What does Haskell use

Answer 11

Haskell uses lazy evaluation
lazy evaluation = call by name + sharing

It defers evaluating arguments until results are needed for computation

Question 12

What is currying

Answer 12

When applying a function with more than 1 argument yields another function with n -1 arguments
This allows the creation of new functions via partial functions

Question 13

Curry type

Answer 13

((a,b) -> c ) -> a -> b -> c

Question 14

uncurry

Answer 14

(a -> b ->c ) -> (a,b) -> c