Elance Clojure Test Answers 2015
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What is Clojure a dialect of?
Scheme
Lisp
Cobra
C/C++
True or False? Clojure is NOT an imperative
language.
True
False
Vars _____
manage independent, synchronous changes to a single
location
provide thread-local variable bindings
manage independent, asynchronous changes to a
single location
provide thread-isolated transactions
(= (map + '(1 2 3)) 3)
True
(1 2 3)
False
6
5
________ evaluates all of the expressions
provided to it in order and yields the last expression's value as its value.
fn
do
def
let
To calculate the average of some numbers in
Clojure, your code would look like this:
def average (numbers): return sum( numbers) / len(
numbers)
public static double average (double[] numbers) { double
sum = 0; for (int i = 0; i < numbers.length; i + +) { sum + = numbers[ i]; }
return sum / numbers.length; }
(defn average [numbers] (/ (apply + numbers) (count
numbers)))
def average (numbers) numbers.inject(: +) /
numbers.length end
Which is an example of a Clojure function
call?
function-name (arg1, arg2, arg3)
(method-name arg1 arg2 arg3)
(function-name arg1 arg2 arg3)
methodName(arg1, arg2, arg3)
True or False? Arity is the number of
arguments a function can handle.
True
False
True or False? Clojure a functional language.
False
True
What type does the following code result in?
{:a 1 "b" 2}
List
Vector
Map
Array
True or False? In Clojure a symbol can contain
characters that most imperative languages don't allow in variable names.
(Example: in Clojure you can have a symbol with the name +a-.)
True
False
True or False? The Clojure language is
homoiconic.
True
False
The two comment types that are defined by the
reader are:
basic comments and source comments
Single-line comments and Form-level comments
textual comments and multi-line comments
custom comments and code-snippets
Leiningen uses _____ to locate and manage
project dependencies
Maven
GitHub
SourceForge
Ivy
What are sequences?
Specific collections
Concrete lists
Ordered codes
Logical views of collections
What is the syntax of the "if"
function?
(if condition then-expr else-expr)
(condition-if-then-expr-else expr)
(condition to-expr else-expr)
(condition if then-expr else-expr)
What is the function that evaluates a single
argument form?
var
defn
eval
test
Does Clojure have a metadata system that
allows for annotation of symbols and collections?
True
False
True or False? Clojure programs only support
some Java classes and interfaces.
False
True
Which of the following Clojure fragments
calculates (4+2)*(5-3)?
4 2 + 5 3 - *
(+ 4 2 (* (- 5 3)))
4+2*(5-3)
(* (+ 4 2) (- 5 3))
A function can be stored in a var or passed as
an argument to other functions.
False
True
Collections that classically support last-in,
first-out (LIFO) semantics are called ____________.
vectors
indices
stacks
contains
Clojure strings are Java Strings and are
represented in exactly the same way, delimited by double quotes.
FALSE
True
How do you create an anonymous function?
#{items}
#(single-expression)
#(double-expression)
prefix#
What is significant about function names that
end with a "!"?
It serves as a warning that the function in
question may produce an unstable result.
It warns users that the function is deprecated.
All functions that mutate some state must end with
a "!", or else you will get a compiler error.
It is a convention that indicates the function
mutates some state.
Which is a type of collection in Clojure?
Set
None of these
Vector
All of these
How do you add metadata to a symbol or
collection?
{key-value-pairs}
^{key-value-pairs} object
(class-name. args)
#"pattern"
What does the REPL tool do?
Read-enter-print look
Read-eval-part loop
Repeat-eval-pair loop
Read-eval-print loop
True or False? Sets are collections of unique
items. They are better than lists and vectors when duplicates aren't allowed.
False
True
In Clojure, you can create a new class using
_____
gen-class
proxy
All of the above
deftype
Which statement about Clojure macros is true?
Macros are useful, but Clojure's implementation of
them is very limited.
Macros are basically a glorified parameterizable
search-replace mechanism. They are error prone, and should be avoided at all
costs.
Macros provide an ad-hoc mechanism for improving
the performance of critical code.
Macros allow programmers to specify program
transformations that occur during compile time.
Which statement best describes protocols in
Clojure?
A protocol defines how two programs communicate
over a computer network.
A protocol defines an interface. But unlike Java
interfaces, which must be specified when a class is created, protocols can be
attached to a class at any time.
Clojure uses the term "protocol" to refer
to what Java calls an "interface".
Clojure provides several macros that make it easy
to implement various network protocols.
Which of the following code fragments
evaluates to 5?
(get {:a 1 :b 3 :c 5} :c)
({:a 1 :b 3 :c 5} :c)
(:c {:a 1 :b 3 :c 5})
All of the above
What do keywords begin with?
:
-
#
;
What are the 3 phases Clojure code is
processed in?
Read-time, compile-time, run-time
Read-time, gather-time, run-time
There are actually 4 phases.
Read-time, compile-time, load-time
The map function is used to _____
aggregate the elements in a collection using a
given function and return the result as a single value
All of the above
apply a function to all elements in a collection
and return a sequence of the results
create a new Map object containing the specified
elements
If you are already using Java or another JVM
language for RDBMS work, it’s likely that you’re using ______________, easily
the most popular Java object/ relational mapping library.
SLIME
Entity
Korma
Hibernate
lib-noir, Ring, and Compojure are all examples
of Clojure:
HTTP service modules
SOAP service modules
REST service modules
API service modules
JSON service modules
The reduce function is used to _____
All of the above
substract a given amount from an integer value
aggregate the elements in a collection using a
given function and return the result as a single value
apply a function to all elements in a collection
and return a sequence of the results
A built-in Clojure "operation" may
be implemented as a...
Function
Special Form
All of these
Macro
Stack abstraction is supported in Clojure via
what three operations?
conj, pop, peek
get, nth, find
find, conj, get
get, find, pop
REPL stands for _____
Read, Eval, Print, Loop
Read, Eval, Process, Loop
REPresentational Language
Rediscover Enlightened Programs and Languages
The following code will evaluate to true?
(defn +++ [n] (+ (inc n) 1)) (= (+++ 1) 3)
Can't define a reserved symbol
+ is reserved and can't be re-defined
True
Syntax error
False
STM stands for _____
State Transfer Machine
Software Transactional Memory
Safe Transactions in Memory
Step, Translate, Motion
:foo is an example of a(n) _____
keyword
symbol
atom
variable name
Clojure is primarily an imperative language.
True
False
True or False? Metadata is data about data,
and has no effect on the 'host' data.
False
True
True or False? A lazy-sequence can hold all
the possible calculations of the Fibonacci sequence.
True
False
A(n) ________ is a named Emacs object that
represents something editable, usually a file in your filesystem, but also the
Clojure REPL or debugger, for example.
Window
paredit
inferior-lisp
Buffer
What type does the following code result in?
[1 2 3 4]
List
Vector
Map
Array
Clojure provides several
"persistent" data structures. Objects of these classes are _____
stored in a database
implemented in a way that makes them robust in case
of memory errors
immutable
serializable
What is generally the first step in deploying
your Clojure web application?
Installing and configuring Leiningen or setting up
and configuring an app server.
Restarting the application
Copying the .war file your build process is
producing to your server.
Reverting your application's .war file to a prior
version.
How would you want to create a new Atom with
an initial value <value>?
(make-atom <value)
(new-atom value)
(atom <value>)
(new 'Atom <value>)
(new Atom <value>)
We can use _____________ to create a table
with a specific name and define columns.
with-query-results
with-connection
transaction
create-table
Clojure documentation can be accessed
through the clojure.org website
All of the above
via the doc function
on clojuredocs.org
What is the literal syntax for maps?
#{:a 1 :b 2}
{:a 1 :b 2}
[:a 1 :b 2]
A multimethod is created using a ________form,
and implementations of a multimethod are provided by ___________ form.
defmulti, defmethod
defmethod, defmulti
fill, fill-dispatch
derive, make-heiracrchy
Clojure is hosted on the JVM (Java Virtual
Machine) and can use any Java library.
FALSE
True
In many object-oriented languages,
________________ is a way to decouple a class from other objects upon which
that class depends.
chain of responsibility
dependency injection
the template method
strategy pattern
What is the conventional first and last
character used to name vars intended to be bound to new, thread-local values?
(
^
*
"
________ is a very low-level looping and
recursion operation that is usually not necessary.
leap
reduce
map
recur
What's a difference between quote (') and
syntax-quote (`) macro characters?
Quote (') fully qualifies symbols, while
syntax-quote (`) doesn't
There is no difference between quote (') and
syntax-quote (`)
Syntax-quote (`) fully qualifies symbols, while
quote (') doesn't
True or False? Function definitions must
appear before they're first used.
False
True
Which statement about -> and comp is true?
-> is not a valid identifier in clojure, but
comp is
-> is a macro while comp is a higher order
function
comp is a macro while -> is a higher order
function
-> and comp are exactly the same, except the
parameters are in the opposite order
In Clojure, tail-call optimization is _____
only done for simple recursion
done for every call which is in a tail position
impossible
not supported natively by the compiler, but could
be simulated using thunks, trampolines, and macros.
Locks _____
provide thread-local variable bindings
provide thread-isolated transactions
are a low-level construct that should be avoided in
most cases
manage independent, asynchronous changes to a
single location
To represent a boxed decimal in Clojure, you
would use ____________.
float
Float
java.lang.Double
Fixnum
Which statement regarding Clojure
"forms" is true?
Every form is a function call, but not every
function call is a form.
The terms "function call" and "form"
are completely interchangeable.
A form is like a function call, except it invokes a
macro instead.
Every function call is a form, but not every form
is a function call.
What does the "contains?" function
work on?
All of these
Sets
Maps
Vectors
True or False? (reset!) is used to set the
value of an atom.
False
True
In Clojure >= 1.3, which of these follows
the naming conventions for dynamic objects? (def ^:dynamic *d* (atom [])) (def
^:dynamic d (atom []))
d, but not *d*
*d*, but not d
For the following code to evaluate without
error, what needs to be added? (def regex "<a>(.*)</a>")
(re-seq regex "<a>Ryan Kelker</a>")
@ symbol when defining regex
# symbol before the string in regex
Nothing. The syntax is correct
# symbol before regex and after def
# symbol before regex in (re-seq)
You can use ___________ whenever you like if
you need a unique symbol, but its primary role is in helping us write hygienic
macros.
defmacro
hygienic
gensym
important-value
let is a _____
Reserved Keyword
Macro
Special Form
Function
Agents _____
provide thread-isolated transactions
manage independent, asynchronous changes to a
single location
provide thread-local variable bindings
manage independent, synchronous changes to a single
location
Suppose you want to implement a set of
mutually-recursive functions. Which approach might you take?
Define the functions locally using def
Since Clojure only supports simple recursion, you
need to convert to an iterative algorithm.
Define the functions using letfn
Define the functions using let
What provides synchronous changes to a single
piece of shared data?
Atoms
Agents
Refs
Vars
(.split "Java String" " ")
returns
A Java array of strings
A lazy-sequenced array of strings
Syntax error
Invalid operation for string
True or False? In functional oriented
languages, you can't manipulate objects like in object oriented languages.
False
True
What provides synchronous changes to a single,
thread-local value?
Agents
Refs
Atoms
Var
Atoms _____
manage independent, asynchronous changes to a
single location
provide thread-isolated transactions
manage independent, synchronous changes to a single
location
provide thread-local variable bindings
A "dynamic" var _____
has a value that is related to the call stack, and
can be used to pass contextual information between functions that do not call
each other directly
has a value that is shared across multiple threads
must be expected to change value at any time, even
if there is no local code that changes it
is a variable that has mutable state
If you want to create class that extends
another class, you must use _____
reify
deftype
defrecord
gen-class
A _______ is a construct that suspends some
body of code, evaluating it upon demand, when it is "deref"erenced.
deliver
future
delay
promise
Refs _____
provide thread-isolated transactions
provide thread-local variable bindings
manage independent, synchronous changes to a single
location
manage independent, asynchronous changes to a
single location
The Clojure reader can be extended using _____
reader macros
tagged literals
XML
metadata
The application of advice or other aspect
transformations is often called __________.
profiling
advising
weaving
wrapping
How many ways can you safely share mutable
data using Clojure?
5
3
4
2
What's the value returned by... (let [[x y
[z]] [2 4 [8 9]]] (list x y z))
[2 4 [8 9]]
(2 4 8)
(2 4 (8 9))
What is the Closure equivalent to
ClassName.class in Java?
ClassName
ClassName.CLASS
Class.name
(ClassName.class)
(letfn [ (t [] (true? (some true?
["false"])))] (t))
False because the string "false" is not
the value true
False because "false" is not a string
True because "false" is a string
True because "false" is not a string
False because "false" is a string
A Clojure sequence is a Java
Iterator
List
Iterable
Map
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