Erlang Programs (L20) Flashcards
Are there void functions in Erlang?
No, all functions return a value.
For multi-expression function bodies, which expression is returned by the function?
The last expression.
What is wrong the following syntax?
func_name [parm1 parm2 parm3]:
expression_1,
expression_2,
expression_3;
func_name (parm1, parm2, parm3) ->
expression_1,
expression_2,
expression_3.
Invoke the following function:
hello_world () ->
io:fwrite(“Hello World\n”).
hello_world().
Which format specifier is used to print values in natural form (such as ints, floats, etc.) when using io:fwrite ?
~w
Which format specifier is used to print strings when using io:fwrite ?
~s
What happens when a string is printed using the ~w format specifier?
The string’s ASCII values are printed.
In what two ways can newline characters be printed using io:fwrite ?
\n or ~n.
Is the following valid?
io:fwrite(“~w, ~w, ~s~n”, 3, 4.5, “cat”).
False: io:fwrite(“~w, ~w, ~s~n”, [3, 4.5, “cat”]).
Multi arity functions are defined within the same function definition in Erlang.
False, each definition is terminated by a period - these are completely separate definitions.
Can different arities of the same function call one another in Erlang?
Yes.
Can we have multiple variations of a
function, all with the same arity in Erlang?
Yes.
When multiple versions of a
function exists, all with the same arity, how does Erlang decide which to use?
Using pattern matching.
Are multiple variations of a function, all with the same arity, defined separately or within the same Erlang statement?
Within the same statement, as different variations are separated by a semi colon and only the last definition ends in a period.
Define an anonymous function (in Erlang) which returns its single parameter multiplied by 2.
fun (X) -> X * 2 end
Erlang also has a map, reduce, and filter function defined in the lists module, which behave the same way as they do in Clojure.
False - Erlang’s reduce function is called fold.
What is the Erlang equivalent of Clojure’s doseq function?
lists:foreach
Which attribute is used to define an Erlang module? Where is it placed?
-module(mod_name).
Placed atop the module source code file.
What is the default code path in Erlang?
The current working directory and Erlang’s system library location.
In what environment variable should directories be defined in order to add them to the code path? (Erlang)
ERL_LIBS
Functions must be imported from another Erlang module (using -import(…)) in order to use them.
False - importing is optional, but functions must be exported to be callable.
The following successfully exports 3 arities of the baz function.
-export(baz/1, baz/2, baz/3).
False, they must be placed in a list:
-export( [baz/1, baz/2, baz/3] ).
When is an Erlang function considered private?
When it is not specified in the export list.
Where is the -export() attribute placed?
At the top of the source code file.
What does the -import() attribute do?
The import attribute eliminates the need to fully qualify the function with the module name.
Use the import attribute to validate non fully qualified use of the append (arity 1) and map (arity 2) functions from the lists module.
-import(lists, [append/1, map/2]).
Can multiple files be compiled at once using erlc?
Yes.
What command is used to execute compiled Erlang code?
erl
What erl execute option prevents dropping into the interactive Eshell?
-noshell
What commands indicate a module and function combination to load an run?
-s or -run
Can only a module be specified following the -s/-run options?
Yes, in which case the start() function is assumed.
What is the primary difference between -s and -run?
If command line arguments are provided, s will pass them as atoms (constants), while run will pass them as strings.
A second -s option is typically passed with what arguments?
-s init stop
What does the second “-s init stop” do?
Tells erl to shutdown the Erlang environment once the program is finished.
