<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
programming	O
language	O
is	O
said	O
to	O
have	O
first-class	B-Application
functions	I-Application
if	O
it	O
treats	O
functions	O
as	O
first-class	O
citizens	O
.	O
</s>
<s>
This	O
means	O
the	O
language	O
supports	O
passing	O
functions	O
as	O
arguments	O
to	O
other	O
functions	O
,	O
returning	O
them	O
as	O
the	O
values	O
from	O
other	O
functions	O
,	O
and	O
assigning	O
them	O
to	O
variables	O
or	O
storing	O
them	O
in	O
data	B-General_Concept
structures	I-General_Concept
.	O
</s>
<s>
Some	O
programming	O
language	O
theorists	O
require	O
support	O
for	O
anonymous	B-General_Concept
functions	I-General_Concept
(	O
function	B-General_Concept
literals	I-General_Concept
)	O
as	O
well	O
.	O
</s>
<s>
In	O
languages	O
with	O
first-class	B-Application
functions	I-Application
,	O
the	O
names	O
of	O
functions	O
do	O
not	O
have	O
any	O
special	O
status	O
;	O
they	O
are	O
treated	O
like	O
ordinary	O
variables	O
with	O
a	O
function	O
type	O
.	O
</s>
<s>
First-class	B-Application
functions	I-Application
are	O
a	O
necessity	O
for	O
the	O
functional	B-Language
programming	I-Language
style	O
,	O
in	O
which	O
the	O
use	O
of	O
higher-order	B-Language
functions	I-Language
is	O
a	O
standard	O
practice	O
.	O
</s>
<s>
There	O
are	O
certain	O
implementation	O
difficulties	O
in	O
passing	O
functions	O
as	O
arguments	O
or	O
returning	O
them	O
as	O
results	O
,	O
especially	O
in	O
the	O
presence	O
of	O
non-local	O
variables	O
introduced	O
in	O
nested	O
and	O
anonymous	B-General_Concept
functions	I-General_Concept
.	O
</s>
<s>
Historically	O
,	O
these	O
were	O
termed	O
the	O
funarg	B-Application
problems	I-Application
,	O
the	O
name	O
coming	O
from	O
"	O
function	O
argument	O
"	O
.	O
</s>
<s>
ALGOL	B-Language
60	I-Language
,	O
Pascal	B-Application
)	O
or	O
omitting	O
nested	O
functions	O
and	O
thus	O
non-local	O
variables	O
(	O
e.g.	O
</s>
<s>
C	B-Language
)	O
.	O
</s>
<s>
The	O
early	O
functional	B-Language
language	I-Language
Lisp	B-Language
took	O
the	O
approach	O
of	O
dynamic	O
scoping	B-Language
,	O
where	O
non-local	O
variables	O
refer	O
to	O
the	O
closest	O
definition	O
of	O
that	O
variable	O
at	O
the	O
point	O
where	O
the	O
function	O
is	O
executed	O
,	O
instead	O
of	O
where	O
it	O
was	O
defined	O
.	O
</s>
<s>
Proper	O
support	O
for	O
lexically	O
scoped	O
first-class	B-Application
functions	I-Application
was	O
introduced	O
in	O
Scheme	B-Language
and	O
requires	O
handling	O
references	O
to	O
functions	O
as	O
closures	B-Language
instead	O
of	O
bare	O
function	B-Language
pointers	I-Language
,	O
which	O
in	O
turn	O
makes	O
garbage	B-General_Concept
collection	I-General_Concept
a	O
necessity	O
.	O
</s>
<s>
In	O
this	O
section	O
,	O
we	O
compare	O
how	O
particular	O
programming	O
idioms	O
are	O
handled	O
in	O
a	O
functional	B-Language
language	I-Language
with	O
first-class	B-Application
functions	I-Application
(	O
Haskell	B-Language
)	O
compared	O
to	O
an	O
imperative	O
language	O
where	O
functions	O
are	O
second-class	O
citizens	O
(	O
C	B-Language
)	O
.	O
</s>
<s>
In	O
languages	O
where	O
functions	O
are	O
first-class	O
citizens	O
,	O
functions	O
can	O
be	O
passed	O
as	O
arguments	O
to	O
other	O
functions	O
in	O
the	O
same	O
way	O
as	O
other	O
values	O
(	O
a	O
function	O
taking	O
another	O
function	O
as	O
argument	O
is	O
called	O
a	O
higher-order	B-Language
function	I-Language
)	O
.	O
</s>
<s>
In	O
the	O
language	O
Haskell	B-Language
:	O
</s>
<s>
Languages	O
where	O
functions	O
are	O
not	O
first-class	O
often	O
still	O
allow	O
one	O
to	O
write	O
higher-order	B-Language
functions	I-Language
through	O
the	O
use	O
of	O
features	O
such	O
as	O
function	B-Language
pointers	I-Language
or	O
delegates	O
.	O
</s>
<s>
In	O
the	O
language	O
C	B-Language
:	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
differences	O
between	O
the	O
two	O
approaches	O
that	O
are	O
not	O
directly	O
related	O
to	O
the	O
support	O
of	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
The	O
Haskell	B-Language
sample	O
operates	O
on	O
lists	O
,	O
while	O
the	O
C	B-Language
sample	O
operates	O
on	O
arrays	B-Data_Structure
.	O
</s>
<s>
Both	O
are	O
the	O
most	O
natural	O
compound	O
data	B-General_Concept
structures	I-General_Concept
in	O
the	O
respective	O
languages	O
and	O
making	O
the	O
C	B-Language
sample	O
operate	O
on	O
linked	O
lists	O
would	O
have	O
made	O
it	O
unnecessarily	O
complex	O
.	O
</s>
<s>
This	O
also	O
accounts	O
for	O
the	O
fact	O
that	O
the	O
C	B-Language
function	O
needs	O
an	O
additional	O
parameter	O
(	O
giving	O
the	O
size	O
of	O
the	O
array	O
.	O
)	O
</s>
<s>
The	O
C	B-Language
function	O
updates	O
the	O
array	O
in-place	B-Algorithm
,	O
returning	O
no	O
value	O
,	O
whereas	O
in	O
Haskell	B-Language
data	B-General_Concept
structures	I-General_Concept
are	O
persistent	B-Application
(	O
a	O
new	O
list	O
is	O
returned	O
while	O
the	O
old	O
is	O
left	O
intact	O
.	O
)	O
</s>
<s>
The	O
Haskell	B-Language
sample	O
uses	O
recursion	O
to	O
traverse	O
the	O
list	O
,	O
while	O
the	O
C	B-Language
sample	O
uses	O
iteration	B-Algorithm
.	O
</s>
<s>
Again	O
,	O
this	O
is	O
the	O
most	O
natural	O
way	O
to	O
express	O
this	O
function	O
in	O
both	O
languages	O
,	O
but	O
the	O
Haskell	B-Language
sample	O
could	O
easily	O
have	O
been	O
expressed	O
in	O
terms	O
of	O
a	O
fold	B-Application
and	O
the	O
C	B-Language
sample	O
in	O
terms	O
of	O
recursion	O
.	O
</s>
<s>
Finally	O
,	O
the	O
Haskell	B-Language
function	O
has	O
a	O
polymorphic	B-Application
type	O
,	O
as	O
this	O
is	O
not	O
supported	O
by	O
C	B-Language
we	O
have	O
fixed	O
all	O
type	O
variables	O
to	O
the	O
type	O
constant	O
int	O
.	O
</s>
<s>
In	O
languages	O
supporting	O
anonymous	B-General_Concept
functions	I-General_Concept
,	O
we	O
can	O
pass	O
such	O
a	O
function	O
as	O
an	O
argument	O
to	O
a	O
higher-order	B-Language
function	I-Language
:	O
</s>
<s>
In	O
a	O
language	O
which	O
does	O
not	O
support	O
anonymous	B-General_Concept
functions	I-General_Concept
,	O
we	O
have	O
to	O
bind	O
it	O
to	O
a	O
name	O
instead	O
:	O
</s>
<s>
Once	O
we	O
have	O
anonymous	B-General_Concept
or	O
nested	O
functions	O
,	O
it	O
becomes	O
natural	O
for	O
them	O
to	O
refer	O
to	O
variables	O
outside	O
of	O
their	O
body	O
(	O
called	O
non-local	O
variables	O
)	O
:	O
</s>
<s>
If	O
functions	O
are	O
represented	O
with	O
bare	O
function	B-Language
pointers	I-Language
,	O
we	O
can	O
not	O
know	O
anymore	O
how	O
the	O
value	O
that	O
is	O
outside	O
of	O
the	O
function	O
's	O
body	O
should	O
be	O
passed	O
to	O
it	O
,	O
and	O
because	O
of	O
that	O
a	O
closure	B-Language
needs	O
to	O
be	O
built	O
manually	O
.	O
</s>
<s>
If	O
f	O
would	O
have	O
been	O
a	O
nested	O
function	O
we	O
would	O
still	O
have	O
run	O
into	O
the	O
same	O
problem	O
and	O
this	O
is	O
the	O
reason	O
they	O
are	O
not	O
supported	O
in	O
C	B-Language
.	O
</s>
<s>
When	O
returning	O
a	O
function	O
,	O
we	O
are	O
in	O
fact	O
returning	O
its	O
closure	B-Language
.	O
</s>
<s>
In	O
the	O
C	B-Language
example	O
any	O
local	O
variables	O
captured	O
by	O
the	O
closure	B-Language
will	O
go	B-Application
out	O
of	O
scope	O
once	O
we	O
return	O
from	O
the	O
function	O
that	O
builds	O
the	O
closure	B-Language
.	O
</s>
<s>
Forcing	O
the	O
closure	B-Language
at	O
a	O
later	O
point	O
will	O
result	O
in	O
undefined	O
behaviour	O
,	O
possibly	O
corrupting	O
the	O
stack	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
the	O
upwards	B-Application
funarg	I-Application
problem	I-Application
.	O
</s>
<s>
Assigning	O
functions	O
to	O
variables	O
and	O
storing	O
them	O
inside	O
(	O
global	O
)	O
datastructures	B-General_Concept
potentially	O
suffers	O
from	O
the	O
same	O
difficulties	O
as	O
returning	O
functions	O
.	O
</s>
<s>
Under	O
this	O
definition	O
of	O
equality	O
,	O
for	O
example	O
,	O
any	O
two	O
implementations	O
of	O
a	O
stable	O
sorting	O
algorithm	O
,	O
such	O
as	O
insertion	B-Algorithm
sort	I-Algorithm
and	O
merge	B-Algorithm
sort	I-Algorithm
,	O
would	O
be	O
considered	O
equal	O
.	O
</s>
<s>
This	O
kind	O
of	O
equality	O
could	O
be	O
implemented	O
in	O
interpreted	B-Application
languages	I-Application
by	O
comparing	O
the	O
source	O
code	O
of	O
the	O
function	O
bodies	O
(	O
such	O
as	O
in	O
Interpreted	O
Lisp	B-Language
1.5	I-Language
)	O
or	O
the	O
object	B-Language
code	I-Language
in	O
compiled	B-Language
languages	I-Language
.	O
</s>
<s>
Intensional	O
equality	O
implies	O
extensional	O
equality	O
(	O
assuming	O
the	O
functions	O
are	O
deterministic	O
and	O
have	O
no	O
hidden	O
inputs	O
,	O
such	O
as	O
the	O
program	B-General_Concept
counter	I-General_Concept
or	O
a	O
mutable	O
global	O
variable	O
.	O
)	O
</s>
<s>
All	O
functions	O
or	O
closures	B-Language
are	O
assigned	O
a	O
unique	O
identifier	O
(	O
usually	O
the	O
address	O
of	O
the	O
function	O
body	O
or	O
the	O
closure	B-Language
)	O
and	O
equality	O
is	O
decided	O
based	O
on	O
equality	O
of	O
the	O
identifier	O
.	O
</s>
<s>
Referential	O
equality	O
breaks	O
referential	O
transparency	O
and	O
is	O
therefore	O
not	O
supported	O
in	O
pure	O
languages	O
,	O
such	O
as	O
Haskell	B-Language
.	O
</s>
<s>
In	O
the	O
Curry	O
–	O
Howard	O
correspondence	O
,	O
function	O
types	O
are	O
related	O
to	O
logical	O
implication	O
;	O
lambda	B-General_Concept
abstraction	O
corresponds	O
to	O
discharging	O
hypothetical	O
assumptions	O
and	O
function	O
application	O
corresponds	O
to	O
the	O
modus	O
ponens	O
inference	O
rule	O
.	O
</s>
<s>
Besides	O
the	O
usual	O
case	O
of	O
programming	O
functions	O
,	O
type	O
theory	O
also	O
uses	O
first-class	B-Application
functions	I-Application
to	O
model	O
associative	B-Application
arrays	I-Application
and	O
similar	O
data	B-General_Concept
structures	I-General_Concept
.	O
</s>
<s>
In	O
category-theoretical	O
accounts	O
of	O
programming	O
,	O
the	O
availability	O
of	O
first-class	B-Application
functions	I-Application
corresponds	O
to	O
the	O
closed	O
category	O
assumption	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
simply	O
typed	O
lambda	B-General_Concept
calculus	O
corresponds	O
to	O
the	O
internal	O
language	O
of	O
Cartesian	B-Application
closed	I-Application
categories	I-Application
.	O
</s>
<s>
Functional	B-Language
programming	I-Language
languages	I-Language
,	O
such	O
as	O
Erlang	B-Operating_System
,	O
Scheme	B-Language
,	O
ML	B-Language
,	O
Haskell	B-Language
,	O
F#	B-Operating_System
,	O
and	O
Scala	B-Application
,	O
all	O
have	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
When	O
Lisp	B-Language
,	O
one	O
of	O
the	O
earliest	O
functional	B-Language
languages	I-Language
,	O
was	O
designed	O
,	O
not	O
all	O
aspects	O
of	O
first-class	B-Application
functions	I-Application
were	O
then	O
properly	O
understood	O
,	O
resulting	O
in	O
functions	O
being	O
dynamically	B-Language
scoped	I-Language
.	O
</s>
<s>
The	O
later	O
Scheme	B-Language
and	O
Common	B-Language
Lisp	I-Language
dialects	O
do	O
have	O
lexically	O
scoped	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
Many	O
scripting	O
languages	O
,	O
including	O
Perl	B-Language
,	O
Python	B-Language
,	O
PHP	B-Application
,	O
Lua	B-Language
,	O
Tcl/Tk	B-Operating_System
,	O
JavaScript	B-Language
and	O
Io	B-Application
,	O
have	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
For	O
imperative	O
languages	O
,	O
a	O
distinction	O
has	O
to	O
be	O
made	O
between	O
Algol	O
and	O
its	O
descendants	O
such	O
as	O
Pascal	B-Application
,	O
the	O
traditional	O
C	B-Language
family	O
,	O
and	O
the	O
modern	O
garbage-collected	O
variants	O
.	O
</s>
<s>
The	O
Algol	O
family	O
has	O
allowed	O
nested	O
functions	O
and	O
higher-order	O
taking	O
function	O
as	O
arguments	O
,	O
but	O
not	O
higher-order	B-Language
functions	I-Language
that	O
return	O
functions	O
as	O
results	O
(	O
except	O
Algol	B-Language
68	I-Language
,	O
which	O
allows	O
this	O
)	O
.	O
</s>
<s>
The	O
reason	O
for	O
this	O
was	O
that	O
it	O
was	O
not	O
known	O
how	O
to	O
deal	O
with	O
non-local	O
variables	O
if	O
a	O
nested-function	O
was	O
returned	O
as	O
a	O
result	O
(	O
and	O
Algol	B-Language
68	I-Language
produces	O
runtime	O
errors	O
in	O
such	O
cases	O
)	O
.	O
</s>
<s>
The	O
C	B-Language
family	O
allowed	O
both	O
passing	O
functions	O
as	O
arguments	O
and	O
returning	O
them	O
as	O
results	O
,	O
but	O
avoided	O
any	O
problems	O
by	O
not	O
supporting	O
nested	O
functions	O
.	O
</s>
<s>
As	O
the	O
usefulness	O
of	O
returning	O
functions	O
primarily	O
lies	O
in	O
the	O
ability	O
to	O
return	O
nested	O
functions	O
that	O
have	O
captured	O
non-local	O
variables	O
,	O
instead	O
of	O
top-level	O
functions	O
,	O
these	O
languages	O
are	O
generally	O
not	O
considered	O
to	O
have	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
Modern	O
imperative	O
languages	O
often	O
support	O
garbage-collection	O
making	O
the	O
implementation	O
of	O
first-class	B-Application
functions	I-Application
feasible	O
.	O
</s>
<s>
First-class	B-Application
functions	I-Application
have	O
often	O
only	O
been	O
supported	O
in	O
later	O
revisions	O
of	O
the	O
language	O
,	O
including	O
C#	B-Application
2.0	O
and	O
Apple	O
's	O
Blocks	B-Language
extension	O
to	O
C	B-Language
,	O
C++	B-Language
,	O
and	O
Objective-C	B-Language
.	O
C++11	B-Language
has	O
added	O
support	O
for	O
anonymous	B-General_Concept
functions	I-General_Concept
and	O
closures	B-Language
to	O
the	O
language	O
,	O
but	O
because	O
of	O
the	O
non-garbage	O
collected	O
nature	O
of	O
the	O
language	O
,	O
special	O
care	O
has	O
to	O
be	O
taken	O
for	O
non-local	O
variables	O
in	O
functions	O
to	O
be	O
returned	O
as	O
results	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Language	O
Higher-order	B-Language
functions	I-Language
Nested	O
functions	O
Non-local	O
variables	O
Notes	O
Arguments	O
Results	O
Named	O
Anonymous	B-General_Concept
Closures	B-Language
Partial	B-Application
application	I-Application
Algol	O
family	O
ALGOL	B-Language
60	I-Language
Have	O
function	O
types	O
.	O
</s>
<s>
ALGOL	B-Language
68	I-Language
Pascal	B-Application
Ada	B-Language
Oberon	B-Language
Delphi	B-Language
C	B-Language
family	O
C	B-Language
Has	O
function	B-Language
pointers	I-Language
.	O
</s>
<s>
C++	B-Language
Doc	O
No	O
.	O
</s>
<s>
1968	O
:	O
V	O
Samko	O
;	O
J	O
Willcock	O
,	O
J	O
Järvi	O
,	O
D	O
Gregor	O
,	O
A	O
Lumsdaine	O
(	O
February	O
26	O
,	O
2006	O
)	O
Lambda	B-General_Concept
expressions	I-General_Concept
and	O
closures	B-Language
for	O
C++	B-Language
Has	O
function	B-Language
pointers	I-Language
,	O
function	B-Language
objects	I-Language
.	O
</s>
<s>
Explicit	O
partial	B-Application
application	I-Application
possible	O
with	O
std::bind	O
.	O
</s>
<s>
C#	B-Application
Has	O
delegates	O
(	O
2.0	O
)	O
and	O
lambda	B-General_Concept
expressions	I-General_Concept
(	O
3.0	O
)	O
.	O
</s>
<s>
Objective-C	B-Language
Has	O
function	B-Language
pointers	I-Language
.	O
</s>
<s>
Java	B-Language
Has	O
anonymous	B-General_Concept
inner	O
classes	O
.	O
</s>
<s>
Go	B-Application
Limbo	B-Application
Newsqueak	B-Language
Rust	B-Application
Functional	B-Language
languages	I-Language
Lisp	B-Language
(	O
see	O
below	O
)	O
Scheme	B-Language
Julia	B-Application
Clojure	B-Language
ML	B-Language
Haskell	B-Language
jq	B-Language
Scala	B-Application
Erlang	B-Operating_System
F#	B-Operating_System
OCaml	B-Language
Scripting	O
languages	O
Io	B-Application
JavaScript	B-Language
Partial	B-Application
application	I-Application
possible	O
with	O
user-land	O
code	O
on	O
ES3	O
Lua	B-Language
PHP	B-Application
Partial	B-Application
application	I-Application
possible	O
with	O
user-land	O
code	O
.	O
</s>
<s>
Perl	B-Language
Python	B-Language
(	O
see	O
below	O
)	O
Ruby	B-Language
(	O
see	O
below	O
)	O
Other	O
languages	O
Fortran	B-Application
Maple	B-Language
Mathematica	B-Language
MATLAB	B-Language
Partial	B-Application
application	I-Application
possible	O
by	O
automatic	O
generation	O
of	O
new	O
functions.Partial	O
Function	O
Evaluation	O
in	O
MATLAB	B-Language
Smalltalk	B-Application
Partial	B-Application
application	I-Application
possible	O
through	O
library	O
.	O
</s>
<s>
C++	B-Language
C++11	B-Language
closures	B-Language
can	O
capture	O
non-local	O
variables	O
by	O
copy	O
construction	O
,	O
by	O
reference	O
(	O
without	O
extending	O
their	O
lifetime	O
)	O
,	O
or	O
by	O
move	O
construction	O
(	O
the	O
variable	O
lives	O
as	O
long	O
as	O
the	O
closure	B-Language
does	O
)	O
.	O
</s>
<s>
The	O
first	O
option	O
is	O
safe	O
if	O
the	O
closure	B-Language
is	O
returned	O
but	O
requires	O
a	O
copy	O
and	O
cannot	O
be	O
used	O
to	O
modify	O
the	O
original	O
variable	O
(	O
which	O
might	O
not	O
exist	O
any	O
more	O
at	O
the	O
time	O
the	O
closure	B-Language
is	O
called	O
)	O
.	O
</s>
<s>
The	O
second	O
option	O
potentially	O
avoids	O
an	O
expensive	O
copy	O
and	O
allows	O
to	O
modify	O
the	O
original	O
variable	O
but	O
is	O
unsafe	O
in	O
case	O
the	O
closure	B-Language
is	O
returned	O
(	O
see	O
dangling	B-Error_Name
references	I-Error_Name
)	O
.	O
</s>
<s>
The	O
third	O
option	O
is	O
safe	O
if	O
the	O
closure	B-Language
is	O
returned	O
and	O
does	O
not	O
require	O
a	O
copy	O
but	O
cannot	O
be	O
used	O
to	O
modify	O
the	O
original	O
variable	O
either	O
.	O
</s>
<s>
Java	B-Language
Java	B-Language
8	O
closures	B-Language
can	O
only	O
capture	O
final	O
or	O
"	O
effectively	O
final	O
"	O
non-local	O
variables	O
.	O
</s>
<s>
Java	B-Language
's	O
function	O
types	O
are	O
represented	O
as	O
Classes	O
.	O
</s>
<s>
Anonymous	B-General_Concept
functions	I-General_Concept
take	O
the	O
type	O
inferred	O
from	O
the	O
context	O
.	O
</s>
<s>
Lexically	O
scoped	O
Lisp	B-Language
variants	O
support	O
closures	B-Language
.	O
</s>
<s>
Dynamically	B-Language
scoped	I-Language
variants	O
do	O
not	O
support	O
closures	B-Language
or	O
need	O
a	O
special	O
construct	O
to	O
create	O
closures	B-Language
.	O
</s>
<s>
In	O
Common	B-Language
Lisp	I-Language
,	O
the	O
identifier	O
of	O
a	O
function	O
in	O
the	O
function	O
namespace	O
cannot	O
be	O
used	O
as	O
a	O
reference	O
to	O
a	O
first-class	O
value	O
.	O
</s>
<s>
The	O
special	O
operator	O
function	O
must	O
be	O
used	O
to	O
retrieve	O
the	O
function	O
as	O
a	O
value	O
:	O
(	O
function	O
foo	O
)	O
evaluates	O
to	O
a	O
function	B-Language
object	I-Language
.	O
</s>
<s>
To	O
apply	O
such	O
a	O
function	B-Language
object	I-Language
,	O
one	O
must	O
use	O
the	O
funcall	O
function	O
:	O
(	O
funcall	O
#'foo	O
bar	O
baz	O
)	O
.	O
</s>
<s>
Explicit	O
partial	B-Application
application	I-Application
with	O
functools.partial	O
since	O
version	O
2.5	O
,	O
and	O
operator.methodcaller	O
since	O
version	O
2.6	O
.	O
</s>
<s>
The	O
identifier	O
of	O
a	O
regular	O
"	O
function	O
"	O
in	O
Ruby	B-Language
(	O
which	O
is	O
really	O
a	O
method	O
)	O
cannot	O
be	O
used	O
as	O
a	O
value	O
or	O
passed	O
.	O
</s>
<s>
The	O
syntax	O
for	O
calling	O
such	O
a	O
function	B-Language
object	I-Language
differs	O
from	O
calling	O
regular	O
methods	O
.	O
</s>
