Drill 6 Solution

Question 1

Fill in the blanks in the following lambda expression. The lambda should take two Numbers as inputs and return a Number that's the product of the two input Numbers.

<a>(<b>): x * y <c>

a: ____

b: ____

c: ____

Answer

a: lam

b: x, y or y, x

c: end

Question 2

Can all lambda expressions be rewritten as functions?

( ) Yes
( ) No

Answer

(X) Yes
( ) No

You can think of lambda expressions as short-hand for one-line functions.

Question 3

What will happen if we write the following in the definitions window and then click 'Run'?

Try to answer without using Pyret.

num = 5
square = lam(n): n * n end
square(num)

( ) 25 will be output in the interactions window
( ) Nothing
( ) "The declaration of the identifier named num shadows a previous declaration of an identifier also named num"
( ) Error: "The identifier 'num' is unbound"
( ) Error: "The declaration of the identifier named square shadows a previous declaration of an identifier also named square"

Answer

(X) 25 will be output in the interactions window
( ) Nothing
( ) "The declaration of the identifier named num shadows a previous declaration of an identifier also named num"
( ) Error: "The identifier 'num' is unbound"
( ) Error: "The declaration of the identifier named square shadows a previous declaration of an identifier also named square"

Since square(num) is 25.

Question 4

What concept from this week of class is least clear to you?