Intro to Erlang (L19)

Question 1

What is Erlang known for?

Answer 1

Erlang is the king / queen of concurrent languages.

Question 2

Which concurrency framework is based directly upon the Erlang language?

Answer 2

Java’s Akka concurrency framework.

Question 3

Like Clojure, Erlang is a direct mapping of the LISP language.

Answer 3

False.

Question 4

Erlang runs on which virtual machine?

Answer 4

BEAM.

Question 5

Name a language that run’s on Erlang’s virtual machine.

Answer 5

Elixir.

Question 6

What’s the name of Erlang’s interactive command line?

Answer 6

Eshell.

Question 7

What is the suffix of a compiled Erlang file?

Answer 7

.beam

Question 8

What command is used to compile Erlang code?

Answer 8

erlc

Question 9

What command is used to run compiled Erlang code?

Answer 9

erl

Question 10

What is the suffix of a Erlang source file?

Answer 10

.erl

Question 11

Are there type declarations in Erlang?

Answer 11

No - types are inferred from context.

Question 12

What are Erlang’s simple types?

Answer 12

Integers, floating point values, strings.

Question 13

What is the max size of Erlang’s integers?

Answer 13

Erlang’s integers are of arbitrary length.

Question 14

Do Erlang strings use single or double quotes?

Answer 14

Double.

Question 15

Is there a boolean type in Erlang?

Answer 15

No, but there are true/false constants that are returned by conditional checks.

Question 16

Erlang uses prefix notation for its operations.

Answer 16

False.

Question 17

Erlang variables can only be reassigned once.

Answer 17

False, they can only be assigned once - attempts to reassign generate errors.

Question 18

Erlang variables must begin with what?

Answer 18

A capital letter.

Question 19

When are commas used in Erlang?

Answer 19

Commas are used between function arguments and between expressions in a function body.

Question 20

When are semi colons used in Erlang?

Answer 20

Semi-colons are used between alternate forms of a function.

Question 21

When are periods used in Erlang?

Answer 21

A period (plus a whitespace char like a newline) is used to terminate a complete expression.

Question 22

What are Erlang’s 4 composite data structures?

Answer 22

Tuple, list, record, map.

Question 23

Erlang tuples are analogous to what data type in C?

Answer 23

structs

Question 24

Define a tuple with 2 elements.

Answer 24

{1, 2}

Question 25

In practice, what is the first element of an Erlang tuple?

Answer 25

An atom.

Question 26

What are atoms?

Answer 26

Constant labels/strings.

Question 27

What is the syntax restriction of Erlang atoms?

Answer 27

They must begin with a lowercase character.

Question 28

What character is used for comments in Erlang?

Answer 28

%

Question 29

Use pattern matching to save (only) the pig’s age to another variable.
P = {pig, “Jim”, 43}.

Answer 29

{pig, _ , Age} = P.

Question 30

Define an Erlang list of two values.

Answer 30

List1 = [1, 2].

Question 31

Can types be mixed in Erlang lists?

Answer 31

Yes.

Question 32

What is stored in List2?
List1 = [1, 2].
List2 = [“x” | List1].

Answer 32

[“x”, 1, 2]

Question 33

What do X and Y equal to?
List1 = [1, 2, 3].
[ X | Y ] = List1.

Answer 33

X = 1 (head), Y = [2, 3] (tail).

Question 34

What function produces List3 from List1 and List2?
List1 = [1, 2, 3].
List2 = [4, 5, 6].
List3 = [1, 2, 3, 4, 5, 6].

Answer 34

List3= lists:append(List1, List2).

Question 35

What function deletes all ocurences of an element from a list?

Answer 35

Result = lists:delete(Element, List).

Question 36

What function sorts an Erlang list?

Answer 36

SortedList = lists:sort(UnsortedList).

Question 37

Does Erlang’s sort function sort in increasing or decreasing order by default?

Answer 37

Increasing.

Question 38

What function splits an Erlang list into two lists at a specified index?

Answer 38

{Prefix, Suffix} = lists:split(Position, List).

Question 39

What function reverse an Erlang list?

Answer 39

Reversed = lists:reverse(List).

Question 40

How do you define a record in Erlang?

Answer 40

-record(name, {
key1 = val1,
key2 = val2,
}).

Question 41

Record keys and values may be of any type in Erlang.

Answer 41

False - keys must be atoms.

Question 42

The name of a record must be an atom.

Answer 42

True.

Question 43

In the below record definition, val1 and val2 are necessarily the values of key1 & key2 once this record is “instantiated”:
-record(name, {
key1 = val1,
key2 = val2,
}).

Answer 43

False, val1 & val2 are default values for key1 & key2, respectively.

Question 44

Must a key be given a default value in an Erlang record definition?

Answer 44

No.

Question 45

What is the value of R1’s age?
-record(person, {name = unknown, age}).
R1 = #person{}.

Answer 45

Age is undefined.

Question 46

Create a record wherein age is defined explicitily, using the definition below.
-record(person, {name = unknown, age}).

Answer 46

R1 = #person{age = 99}.

Question 47

Access the “age” field of a “person” record stored in variable R1.

Answer 47

Age = R1#person.age.

Question 48

Where are record declarations generally declared?

Answer 48

In separate file(s), and then included in the current files.

Question 49

Included files in Erlang are given what extension?

Answer 49

.hrl

Question 50

Write the code to import declarations from an external file called “person.hrl”.

Answer 50

-include(“person.hrl”).

Question 51

Define the same map using two different syntaxes.

Answer 51

M1 = #{man => “joe”, women => “sue”}.
M2 = #{man := “joe”, women := “sue”}.