Question

1. If an F# function has type 'a -> 'b when 'a : comparison, which of the following is not a legal type for it? Select one:

A.(float -> float) -> bool

B.string -> (int -> int)

C.int -> int

D.int list -> bool list

Answer 1

B. string -> (int -> int)

Step-by-step explanation:

We are going to perform comparison operations '->'. It is important to notice that the comparison operation gives us a bool value (True or False) and the comparison operation is legal if and only if the data types to be compared are the same.

Example:

int(4)->int(5) False

int(4)->int(4) True

int(4)->string(4) Error, data types don't match

For this reason:

• A. Is legal because float -> float evaluates to True, True is a boolean value and bool -> bool is legal because both are the same data type.

• B. Is illegal because int -> int evaluates to True, True is a boolean value and string is not a boolean (string -> bool).

• C. Is legal because int is the same type than int.

• D. Is legal because the list is the same type than list regardless it's content.

Note:

The operations inside parentheses are evaluated first.

List is a type by itself regardless of its content.