<s>
Haskell	B-Language
(	O
)	O
is	O
a	O
general-purpose	B-Language
,	O
statically-typed	O
,	O
purely	B-Application
functional	I-Application
programming	I-Application
language	O
with	O
type	O
inference	O
and	O
lazy	O
evaluation	O
.	O
</s>
<s>
Designed	O
for	O
teaching	O
,	O
research	O
and	O
industrial	O
applications	O
,	O
Haskell	B-Language
has	O
pioneered	O
a	O
number	O
of	O
programming	O
language	O
features	O
such	O
as	O
type	O
classes	O
,	O
which	O
enable	O
type-safe	B-Language
operator	O
overloading	B-Application
,	O
and	O
monadic	O
IO	B-General_Concept
.	O
</s>
<s>
Haskell	B-Language
's	O
main	O
implementation	O
is	O
the	B-Application
Glasgow	I-Application
Haskell	I-Application
Compiler	I-Application
(	O
GHC	B-Application
)	O
.	O
</s>
<s>
It	O
is	O
named	O
after	O
logician	O
Haskell	B-Language
Curry	B-Application
.	O
</s>
<s>
Haskell	B-Language
's	O
semantics	B-Application
are	O
historically	O
based	O
on	O
those	O
of	O
the	O
Miranda	B-Language
programming	I-Language
language	I-Language
,	O
which	O
served	O
to	O
focus	O
the	O
efforts	O
of	O
the	O
initial	O
Haskell	B-Language
working	O
group	O
.	O
</s>
<s>
The	O
last	O
formal	O
specification	O
of	O
the	O
language	O
was	O
made	O
in	O
July	O
2010	O
,	O
while	O
the	O
development	O
of	O
GHC	B-Application
continues	O
to	O
expand	O
Haskell	B-Language
via	O
language	O
extensions	O
.	O
</s>
<s>
Haskell	B-Language
is	O
used	O
in	O
academia	O
and	O
industry	O
.	O
</s>
<s>
,	O
Haskell	B-Language
was	O
the	O
28th	O
most	O
popular	O
programming	O
language	O
by	O
Google	B-Application
searches	I-Application
for	O
tutorials	O
,	O
and	O
made	O
up	O
less	O
than	O
1%	O
of	O
active	O
users	O
on	O
the	O
GitHub	B-Application
source	O
code	O
repository	O
.	O
</s>
<s>
Following	O
the	O
release	O
of	O
Miranda	B-Language
by	O
Research	O
Software	O
Ltd	O
.	O
in	O
1985	O
,	O
interest	O
in	O
lazy	O
functional	B-Language
languages	I-Language
grew	O
.	O
</s>
<s>
By	O
1987	O
,	O
more	O
than	O
a	O
dozen	O
non-strict	O
,	O
purely	B-Application
functional	I-Application
programming	I-Application
languages	O
existed	O
.	O
</s>
<s>
Miranda	B-Language
was	O
the	O
most	O
widely	O
used	O
,	O
but	O
it	O
was	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
At	O
the	O
conference	O
on	O
Functional	B-Language
Programming	I-Language
Languages	I-Language
and	O
Computer	O
Architecture	O
(	O
FPCA	O
'	O
87	O
)	O
in	O
Portland	O
,	O
Oregon	O
,	O
there	O
was	O
a	O
strong	O
consensus	O
that	O
a	O
committee	O
be	O
formed	O
to	O
define	O
an	O
open	O
standard	O
for	O
such	O
languages	O
.	O
</s>
<s>
The	O
committee	O
's	O
purpose	O
was	O
to	O
consolidate	O
existing	O
functional	B-Language
languages	I-Language
into	O
a	O
common	O
one	O
to	O
serve	O
as	O
a	O
basis	O
for	O
future	O
research	O
in	O
functional-language	O
design	O
.	O
</s>
<s>
Haskell	B-Language
was	O
developed	O
by	O
a	O
committee	O
,	O
attempting	O
to	O
bring	O
together	O
off	O
the	O
shelf	O
solutions	O
where	O
possible	O
.	O
</s>
<s>
Type	O
classes	O
,	O
which	O
enable	O
type-safe	B-Language
operator	O
overloading	B-Application
,	O
were	O
first	O
proposed	O
by	O
Philip	O
Wadler	O
and	O
Stephen	O
Blott	O
to	O
address	O
the	O
ad-hoc	O
handling	O
of	O
equality	O
types	O
and	O
arithmetic	O
overloading	B-Application
in	O
languages	O
at	O
the	O
time	O
.	O
</s>
<s>
In	O
early	O
versions	O
of	O
Haskell	B-Language
up	O
until	O
and	O
including	O
version	O
1.2	O
,	O
user	O
interaction	O
and	O
IO	B-General_Concept
(	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
)	O
were	O
handled	O
by	O
both	O
streams	O
based	O
and	O
continuation	O
based	O
mechanisms	O
which	O
were	O
widely	O
considered	O
unsatisfactory	O
.	O
</s>
<s>
In	O
version	O
1.3	O
,	O
monadic	O
IO	B-General_Concept
was	O
introduced	O
,	O
along	O
with	O
the	O
generalisation	O
of	O
type	O
classes	O
to	O
higher	O
kinds	O
(	O
type	O
constructors	O
)	O
.	O
</s>
<s>
Along	O
with	O
"	O
do	O
notation	O
"	O
,	O
which	O
provides	O
syntactic	O
sugar	O
for	O
the	O
Monad	O
type	O
class	O
,	O
this	O
gave	O
Haskell	B-Language
an	O
effect	O
system	O
that	O
maintained	O
referential	O
transparency	O
and	O
was	O
convenient	O
.	O
</s>
<s>
Other	O
notable	O
changes	O
in	O
early	O
versions	O
were	O
the	O
approach	O
to	O
the	O
'	O
seq	O
 '	O
function	O
,	O
which	O
creates	O
a	O
data	O
dependency	O
between	O
values	O
,	O
and	O
is	O
used	O
in	O
lazy	B-Language
languages	I-Language
to	O
avoid	O
excessive	O
memory	O
consumption	O
;	O
with	O
it	O
moving	O
from	O
a	O
type	O
class	O
to	O
a	O
standard	O
function	O
to	O
make	O
refactoring	O
more	O
practical	O
.	O
</s>
<s>
The	O
first	O
version	O
of	O
Haskell	B-Language
(	O
"	O
Haskell	B-Language
1.0	O
"	O
)	O
was	O
defined	O
in	O
1990	O
.	O
</s>
<s>
In	O
late	O
1997	O
,	O
the	O
series	O
culminated	O
in	O
Haskell	B-Language
98	I-Language
,	O
intended	O
to	O
specify	O
a	O
stable	O
,	O
minimal	O
,	O
portable	O
version	O
of	O
the	O
language	O
and	O
an	O
accompanying	O
standard	O
library	B-Library
for	O
teaching	O
,	O
and	O
as	O
a	O
base	O
for	O
future	O
extensions	O
.	O
</s>
<s>
The	O
committee	O
expressly	O
welcomed	O
creating	O
extensions	O
and	O
variants	O
of	O
Haskell	B-Language
98	I-Language
via	O
adding	O
and	O
incorporating	O
experimental	O
features	O
.	O
</s>
<s>
In	O
February	O
1999	O
,	O
the	O
Haskell	B-Language
98	I-Language
language	O
standard	O
was	O
originally	O
published	O
as	O
The	O
Haskell	B-Language
98	I-Language
Report	O
.	O
</s>
<s>
In	O
January	O
2003	O
,	O
a	O
revised	O
version	O
was	O
published	O
as	O
Haskell	B-Language
98	I-Language
Language	O
and	O
Libraries	O
:	O
The	O
Revised	O
Report	O
.	O
</s>
<s>
The	O
language	O
continues	O
to	O
evolve	O
rapidly	O
,	O
with	O
the	B-Application
Glasgow	I-Application
Haskell	I-Application
Compiler	I-Application
(	O
GHC	B-Application
)	O
implementation	O
representing	O
the	O
current	O
de	O
facto	O
standard	O
.	O
</s>
<s>
In	O
early	O
2006	O
,	O
the	O
process	O
of	O
defining	O
a	O
successor	O
to	O
the	O
Haskell	B-Language
98	I-Language
standard	O
,	O
informally	O
named	O
Haskell	B-Language
Prime	O
,	O
began	O
.	O
</s>
<s>
The	O
first	O
revision	O
,	O
named	O
Haskell	B-Language
2010	O
,	O
was	O
announced	O
in	O
November	O
2009	O
and	O
published	O
in	O
July	O
2010	O
.	O
</s>
<s>
Haskell	B-Language
2010	O
is	O
an	O
incremental	O
update	O
to	O
the	O
language	O
,	O
mostly	O
incorporating	O
several	O
well-used	O
and	O
uncontroversial	O
features	O
previously	O
enabled	O
via	O
compiler-specific	O
flags	O
.	O
</s>
<s>
This	O
extension	O
was	O
specified	O
in	O
an	O
addendum	O
to	O
Haskell	B-Language
98	I-Language
and	O
was	O
in	O
practice	O
universally	O
used	O
.	O
</s>
<s>
The	O
foreign	B-Application
function	I-Application
interface	I-Application
(	O
FFI	O
)	O
allows	O
bindings	O
to	O
other	O
programming	O
languages	O
.	O
</s>
<s>
Only	O
bindings	O
to	O
C	B-Language
are	O
specified	O
in	O
the	O
Report	O
,	O
but	O
the	O
design	O
allows	O
for	O
other	O
language	O
bindings	O
.	O
</s>
<s>
To	O
support	O
this	O
,	O
data	O
type	O
declarations	O
were	O
permitted	O
to	O
contain	O
no	O
constructors	O
,	O
enabling	O
robust	O
nonce	O
types	O
for	O
foreign	O
data	O
that	O
could	O
not	O
be	O
constructed	O
in	O
Haskell	B-Language
.	O
</s>
<s>
This	O
extension	O
was	O
also	O
previously	O
specified	O
in	O
an	O
Addendum	O
to	O
the	O
Haskell	B-Language
98	I-Language
Report	O
and	O
widely	O
used	O
.	O
</s>
<s>
This	O
syntactic	O
sugar	O
had	O
misleading	O
semantics	B-Application
,	O
in	O
which	O
the	O
code	O
looked	O
like	O
it	O
used	O
the	O
( +	O
)	O
operator	O
,	O
but	O
in	O
fact	O
desugared	O
to	O
code	O
using	O
(	O
-	O
)	O
and	O
(>=	O
)	O
.	O
</s>
<s>
Some	O
syntax	O
issues	O
(	O
changes	O
in	O
the	O
formal	O
grammar	O
)	O
were	O
fixed	O
:	O
pattern	O
guards	O
were	O
added	O
,	O
allowing	O
pattern	B-Language
matching	I-Language
within	O
guards	O
;	O
resolution	O
of	O
operator	O
fixity	O
was	O
specified	O
in	O
a	O
simpler	O
way	O
that	O
reflected	O
actual	O
practice	O
;	O
an	O
edge	O
case	O
in	O
the	O
interaction	O
of	O
the	O
language	O
's	O
lexical	B-Application
syntax	I-Application
of	O
operators	O
and	O
comments	O
was	O
addressed	O
,	O
and	O
the	O
interaction	O
of	O
do-notation	O
and	O
if-then-else	O
was	O
tweaked	O
to	O
eliminate	O
unexpected	O
syntax	O
errors	O
.	O
</s>
<s>
By	O
2010	O
,	O
dozens	O
of	O
extensions	O
to	O
the	O
language	O
were	O
in	O
wide	O
use	O
,	O
and	O
GHC	B-Application
(	O
among	O
other	O
compilers	B-Language
)	O
provided	O
the	O
LANGUAGE	O
pragma	O
to	O
specify	O
individual	O
extensions	O
with	O
a	O
list	O
of	O
identifiers	O
.	O
</s>
<s>
Haskell	B-Language
2010	O
compilers	B-Language
are	O
required	O
to	O
support	O
the	O
Haskell2010	O
extension	O
and	O
are	O
encouraged	O
to	O
support	O
several	O
others	O
,	O
which	O
correspond	O
to	O
extensions	O
added	O
in	O
Haskell	B-Language
2010	O
.	O
</s>
<s>
On	O
29	O
October	O
2021	O
,	O
with	O
GHC	B-Application
version	O
9.2.1	O
,	O
the	O
GHC2021	O
extension	O
was	O
released	O
.	O
</s>
<s>
While	O
this	O
is	O
not	O
a	O
formal	O
language	O
spec	O
,	O
it	O
combines	O
a	O
number	O
of	O
stable	O
,	O
widely-used	O
GHC	B-Application
extensions	O
to	O
Haskell	B-Language
2010	O
.	O
</s>
<s>
Haskell	B-Language
features	O
lazy	O
evaluation	O
,	O
lambda	B-General_Concept
expressions	I-General_Concept
,	O
pattern	B-Language
matching	I-Language
,	O
list	B-Language
comprehension	I-Language
,	O
type	O
classes	O
and	O
type	B-Application
polymorphism	I-Application
.	O
</s>
<s>
It	O
is	O
a	O
purely	B-Application
functional	I-Application
language	O
,	O
which	O
means	O
that	O
functions	O
generally	O
have	O
no	O
side	O
effects	O
.	O
</s>
<s>
Haskell	B-Language
has	O
a	O
strong	O
,	O
static	O
type	O
system	O
based	O
on	O
Hindley	B-Algorithm
–	I-Algorithm
Milner	I-Algorithm
type	I-Algorithm
inference	I-Algorithm
.	O
</s>
<s>
Its	O
principal	O
innovation	O
in	O
this	O
area	O
is	O
type	O
classes	O
,	O
originally	O
conceived	O
as	O
a	O
principled	O
way	O
to	O
add	O
overloading	B-Application
to	O
the	O
language	O
,	O
but	O
since	O
finding	O
many	O
more	O
uses	O
.	O
</s>
<s>
The	O
construct	O
that	O
represents	O
side-effects	O
is	O
an	O
example	O
of	O
a	O
monad	O
:	O
a	O
general	O
framework	O
which	O
can	O
model	O
various	O
computations	O
such	O
as	O
error	O
handling	O
,	O
nondeterminism	O
,	O
parsing	B-Language
and	O
software	B-Operating_System
transactional	I-Operating_System
memory	I-Operating_System
.	O
</s>
<s>
They	O
are	O
defined	O
as	O
ordinary	O
datatypes	O
,	O
but	O
Haskell	B-Language
provides	O
some	O
syntactic	O
sugar	O
for	O
their	O
use	O
.	O
</s>
<s>
Haskell	B-Language
has	O
an	O
open	O
,	O
published	O
specification	O
,	O
and	O
multiple	O
implementations	O
exist	O
.	O
</s>
<s>
Its	O
main	O
implementation	O
,	O
the	B-Application
Glasgow	I-Application
Haskell	I-Application
Compiler	I-Application
(	O
GHC	B-Application
)	O
,	O
is	O
both	O
an	O
interpreter	B-Application
and	O
native-code	B-Language
compiler	B-Language
that	O
runs	O
on	O
most	O
platforms	O
.	O
</s>
<s>
GHC	B-Application
is	O
noted	O
for	O
its	O
rich	O
type	O
system	O
incorporating	O
recent	O
innovations	O
such	O
as	O
generalized	B-Application
algebraic	I-Application
data	I-Application
types	I-Application
and	O
type	O
families	O
.	O
</s>
<s>
The	O
Computer	O
Language	O
Benchmarks	O
Game	O
also	O
highlights	O
its	O
high-performance	O
implementation	O
of	O
concurrency	B-Operating_System
and	O
parallelism	B-Operating_System
.	O
</s>
<s>
An	O
active	O
,	O
growing	O
community	O
exists	O
around	O
the	O
language	O
,	O
and	O
more	O
than	O
5,400	O
third-party	O
open-source	B-Application
libraries	O
and	O
tools	O
are	O
available	O
in	O
the	O
online	O
package	O
repository	O
Hackage	O
.	O
</s>
<s>
program	O
in	O
Haskell	B-Language
(	O
only	O
the	O
last	O
line	O
is	O
strictly	O
necessary	O
)	O
:	O
</s>
<s>
The	O
factorial	O
function	O
in	O
Haskell	B-Language
,	O
defined	O
in	O
a	O
few	O
different	O
ways	O
(	O
the	O
first	O
line	O
is	O
the	O
type	O
annotation	O
,	O
which	O
is	O
optional	O
and	O
is	O
the	O
same	O
for	O
each	O
implementation	O
)	O
:	O
</s>
<s>
As	O
the	O
Integer	O
type	O
has	O
arbitrary-precision	B-Algorithm
,	O
this	O
code	O
will	O
compute	O
values	O
such	O
as	O
factorial	O
100000	O
(	O
a	O
456,574	O
-digit	O
number	O
)	O
,	O
with	O
no	O
loss	O
of	O
precision	O
.	O
</s>
<s>
An	O
implementation	O
of	O
an	O
algorithm	O
similar	O
to	O
quick	B-Algorithm
sort	I-Algorithm
over	O
lists	O
,	O
where	O
the	O
first	O
element	O
is	O
taken	O
as	O
the	O
pivot	O
:	O
</s>
<s>
Implementations	O
that	O
fully	O
or	O
nearly	O
comply	O
with	O
the	O
Haskell	B-Language
98	I-Language
standard	O
,	O
include	O
:	O
</s>
<s>
The	B-Application
Glasgow	I-Application
Haskell	I-Application
Compiler	I-Application
(	O
GHC	B-Application
)	O
compiles	B-Language
to	O
native	B-Language
code	I-Language
on	O
many	O
different	O
processor	O
architectures	O
,	O
and	O
to	O
ANSI	O
C	B-Language
,	O
via	O
one	O
of	O
two	O
intermediate	O
languages	O
:	O
C--	B-Language
,	O
or	O
in	O
more	O
recent	O
versions	O
,	O
LLVM	B-Application
(	O
formerly	O
Low	B-Application
Level	I-Application
Virtual	I-Application
Machine	I-Application
)	O
bitcode	O
.	O
</s>
<s>
GHC	B-Application
has	O
become	O
the	O
de	O
facto	O
standard	O
Haskell	B-Language
dialect	O
.	O
</s>
<s>
There	O
are	O
libraries	O
(	O
e.g.	O
,	O
bindings	O
to	O
OpenGL	B-Application
)	O
that	O
work	O
only	O
with	O
GHC	B-Application
.	O
</s>
<s>
GHC	B-Application
was	O
also	O
distributed	O
with	O
the	O
Haskell	B-Language
platform	I-Language
.	O
</s>
<s>
Jhc	O
,	O
a	O
Haskell	B-Language
compiler	B-Language
written	O
by	O
John	O
Meacham	O
,	O
emphasizes	O
speed	O
and	O
efficiency	O
of	O
generated	O
programs	O
and	O
exploring	O
new	O
program	O
transformations	O
.	O
</s>
<s>
The	O
Utrecht	O
Haskell	B-Language
Compiler	B-Language
(	O
UHC	O
)	O
is	O
a	O
Haskell	B-Language
implementation	O
from	O
Utrecht	O
University	O
.	O
</s>
<s>
It	O
supports	O
almost	O
all	O
Haskell	B-Language
98	I-Language
features	O
plus	O
many	O
experimental	O
extensions	O
.	O
</s>
<s>
It	O
is	O
implemented	O
using	O
attribute	B-Application
grammars	I-Application
and	O
is	O
currently	O
used	O
mostly	O
for	O
research	O
on	O
generated	O
type	O
systems	O
and	O
language	O
extensions	O
.	O
</s>
<s>
The	O
Haskell	B-Language
User	O
's	O
Gofer	B-Application
System	O
(	O
Hugs	B-Application
)	O
is	O
a	O
bytecode	O
interpreter	B-Application
.	O
</s>
<s>
It	O
was	O
once	O
one	O
of	O
the	O
implementations	O
used	O
most	O
widely	O
,	O
alongside	O
the	O
GHC	B-Application
compiler	I-Application
,	O
but	O
has	O
now	O
been	O
mostly	O
replaced	O
by	O
GHCi	B-Application
.	O
</s>
<s>
It	O
also	O
comes	O
with	O
a	O
graphics	O
library	B-Library
.	O
</s>
<s>
HBC	O
is	O
an	O
early	O
implementation	O
supporting	O
Haskell	B-Language
1.4	O
.	O
</s>
<s>
It	O
was	O
implemented	O
by	O
Lennart	O
Augustsson	O
in	O
,	O
and	O
based	O
on	O
,	O
Lazy	B-Language
ML	I-Language
.	O
</s>
<s>
nhc98	O
is	O
a	O
bytecode	O
compiler	B-Language
focusing	O
on	O
minimizing	O
memory	O
use	O
.	O
</s>
<s>
The	O
York	B-Application
Haskell	I-Application
Compiler	I-Application
(	O
Yhc	B-Application
)	O
was	O
a	O
fork	O
of	O
nhc98	O
,	O
with	O
the	O
goals	O
of	O
being	O
simpler	O
,	O
more	O
portable	O
and	O
efficient	O
,	O
and	O
integrating	O
support	O
for	O
Hat	O
,	O
the	O
Haskell	B-Language
tracer	O
.	O
</s>
<s>
It	O
also	O
had	O
a	O
JavaScript	B-Language
backend	O
,	O
allowing	O
users	O
to	O
run	O
Haskell	B-Language
programs	O
in	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
Implementations	O
not	O
fully	O
Haskell	B-Language
98	I-Language
compliant	O
,	O
and	O
using	O
a	O
variant	O
Haskell	B-Language
language	I-Language
,	O
include	O
:	O
</s>
<s>
Eta	O
and	O
Frege	O
are	O
dialects	O
of	O
Haskell	B-Language
targeting	O
the	O
Java	B-Language
Virtual	I-Language
Machine	I-Language
.	O
</s>
<s>
Gofer	B-Application
was	O
an	O
educational	O
dialect	O
of	O
Haskell	B-Language
,	O
with	O
a	O
feature	O
called	O
constructor	O
classes	O
,	O
developed	O
by	O
Mark	O
Jones	O
.	O
</s>
<s>
It	O
was	O
supplanted	O
by	O
Hugs	B-Application
(	O
Haskell	B-Language
User	O
's	O
Gofer	B-Application
System	O
)	O
.	O
</s>
<s>
Helium	O
,	O
a	O
newer	O
dialect	O
of	O
Haskell	B-Language
.	O
</s>
<s>
It	O
currently	O
lacks	O
full	O
support	O
for	O
type	O
classes	O
,	O
rendering	O
it	O
incompatible	O
with	O
many	O
Haskell	B-Language
programs	O
.	O
</s>
<s>
The	O
proof	O
assistant	O
Agda	B-Language
is	O
written	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Cabal	B-Application
is	O
a	O
tool	O
for	O
building	B-Application
and	O
packaging	O
Haskell	B-Language
libraries	O
and	O
programs	O
.	O
</s>
<s>
Darcs	B-Protocol
is	O
a	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
written	O
in	O
Haskell	B-Language
,	O
with	O
several	O
innovative	O
features	O
,	O
such	O
as	O
more	O
precise	O
control	O
of	O
patches	O
to	O
apply	O
.	O
</s>
<s>
GHC	B-Application
is	O
also	O
often	O
a	O
testbed	O
for	O
advanced	O
functional	B-Language
programming	I-Language
features	O
and	O
optimizations	O
in	O
other	O
programming	O
languages	O
.	O
</s>
<s>
Git-annex	B-Protocol
is	O
a	O
tool	O
to	O
manage	O
(	O
big	O
)	O
data	O
files	O
under	O
Git	B-Application
version	B-Architecture
control	I-Architecture
.	O
</s>
<s>
It	O
also	O
provides	O
a	O
distributed	O
file	O
synchronization	O
system	O
(	O
git-annex	B-Protocol
assistant	O
)	O
.	O
</s>
<s>
Linspire	O
Linux	O
chose	O
Haskell	B-Language
for	O
system	O
tools	O
development	O
.	O
</s>
<s>
Pandoc	B-Language
is	O
a	O
tool	O
to	O
convert	O
one	O
markup	O
format	O
into	O
another	O
.	O
</s>
<s>
Pugs	B-Language
is	O
a	O
compiler	B-Language
and	O
interpreter	B-Application
for	O
the	O
Raku	B-Application
programming	O
language	O
(	O
formerly	O
Perl	B-Application
6	I-Application
)	O
.	O
</s>
<s>
TidalCycles	O
is	O
a	O
domain	O
special	O
language	O
for	O
live	O
coding	O
musical	O
patterns	O
,	O
embedded	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Xmonad	B-Device
is	O
a	O
window	B-Application
manager	I-Application
for	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
written	O
fully	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Bluespec	O
SystemVerilog	O
(	O
BSV	O
)	O
is	O
a	O
language	O
for	O
semiconductor	O
design	O
that	O
is	O
an	O
extension	O
of	O
Haskell	B-Language
.	O
</s>
<s>
Also	O
,	O
Bluespec	O
,	O
Inc.	O
'	O
s	O
tools	O
are	O
implemented	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Cryptol	B-Language
,	O
a	O
language	O
and	O
toolchain	O
for	O
developing	O
and	O
verifying	O
cryptography	O
algorithms	O
,	O
is	O
implemented	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Facebook	B-Application
implements	O
its	O
anti-spam	O
programs	O
in	O
Haskell	B-Language
,	O
maintaining	O
the	O
underlying	O
data	O
access	O
library	B-Library
as	O
open-source	B-Application
software	I-Application
.	O
</s>
<s>
The	O
Cardano	B-Protocol
blockchain	I-Protocol
platform	I-Protocol
is	O
implemented	O
in	O
Haskell	B-Language
.	O
</s>
<s>
GitHub	B-Application
implemented	O
Semantic	O
,	O
an	O
open-source	B-Application
library	B-Library
for	O
analysis	O
,	O
diffing	O
,	O
and	O
interpretation	O
of	O
untrusted	O
source	O
code	O
,	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Standard	O
Chartered	O
's	O
financial	O
modelling	O
language	O
Mu	O
is	O
syntactic	O
Haskell	B-Language
running	O
on	O
a	O
strict	O
runtime	O
.	O
</s>
<s>
seL4	O
,	O
the	O
first	O
formally	B-Architecture
verified	I-Architecture
microkernel	B-Operating_System
,	O
used	O
Haskell	B-Language
as	O
a	O
prototyping	O
language	O
for	O
the	O
OS	O
developer	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
the	O
Haskell	B-Language
code	O
defined	O
an	O
executable	O
specification	O
with	O
which	O
to	O
reason	O
,	O
for	O
automatic	O
translation	O
by	O
the	O
theorem-proving	O
tool	O
.	O
</s>
<s>
The	O
Haskell	B-Language
code	O
thus	O
served	O
as	O
an	O
intermediate	O
prototype	O
before	O
final	O
C	B-Language
refinement	O
.	O
</s>
<s>
Target	O
stores	O
 '	O
supply	O
chain	O
optimization	O
software	O
is	O
written	O
in	O
Haskell	B-Language
.	O
</s>
<s>
Notable	O
web	B-Application
frameworks	I-Application
written	O
for	O
Haskell	B-Language
include	O
:	O
</s>
<s>
Bastiaan	O
Heeren	O
,	O
Daan	O
Leijen	O
,	O
and	O
Arjan	O
van	O
IJzendoorn	O
in	O
2003	O
also	O
observed	O
some	O
stumbling	O
blocks	O
for	O
Haskell	B-Language
learners	O
:	O
"	O
The	O
subtle	O
syntax	O
and	O
sophisticated	O
type	O
system	O
of	O
Haskell	B-Language
are	O
a	O
double	O
edged	O
sword	O
–	O
highly	O
appreciated	O
by	O
experienced	O
programmers	O
but	O
also	O
a	O
source	O
of	O
frustration	O
among	O
beginners	O
,	O
since	O
the	O
generality	O
of	O
Haskell	B-Language
often	O
leads	O
to	O
cryptic	O
error	O
messages.	O
"	O
</s>
<s>
To	O
address	O
these	O
,	O
researchers	O
from	O
Utrecht	O
University	O
developed	O
an	O
advanced	O
interpreter	B-Application
called	O
Helium	O
,	O
which	O
improved	O
the	O
user-friendliness	O
of	O
error	O
messages	O
by	O
limiting	O
the	O
generality	O
of	O
some	O
Haskell	B-Language
features	O
,	O
and	O
in	O
particular	O
removing	O
support	O
for	O
type	O
classes	O
.	O
</s>
<s>
Ben	O
Lippmeier	O
designed	O
Disciple	O
as	O
a	O
strict-by-default	B-Language
(	O
lazy	O
by	O
explicit	O
annotation	O
)	O
dialect	O
of	O
Haskell	B-Language
with	O
a	O
type-and-effect	O
system	O
,	O
to	O
address	O
Haskell	B-Language
's	O
difficulties	O
in	O
reasoning	O
about	O
lazy	O
evaluation	O
and	O
in	O
using	O
traditional	O
data	O
structures	O
such	O
as	O
mutable	O
arrays	O
.	O
</s>
<s>
Robert	O
Harper	O
,	O
one	O
of	O
the	O
authors	O
of	O
Standard	B-Language
ML	I-Language
,	O
has	O
given	O
his	O
reasons	O
for	O
not	O
using	O
Haskell	B-Language
to	O
teach	O
introductory	O
programming	O
.	O
</s>
<s>
Among	O
these	O
are	O
the	O
difficulty	O
of	O
reasoning	O
about	O
resource	O
use	O
with	O
non-strict	O
evaluation	O
,	O
that	O
lazy	O
evaluation	O
complicates	O
the	O
definition	O
of	O
datatypes	O
and	O
inductive	O
reasoning	O
,	O
and	O
the	O
"	O
inferiority	O
"	O
of	O
Haskell	B-Language
's	O
(	O
old	O
)	O
class	O
system	O
compared	O
to	O
ML	B-Algorithm
's	O
module	O
system	O
.	O
</s>
<s>
Haskell	B-Language
's	O
build	B-Application
tool	I-Application
,	O
Cabal	B-Application
,	O
has	O
historically	O
been	O
criticized	O
for	O
poorly	O
handling	O
multiple	O
versions	O
of	O
the	O
same	O
library	B-Library
,	O
a	O
problem	O
known	O
as	O
"	O
Cabal	B-Application
hell	O
"	O
.	O
</s>
<s>
The	O
Stackage	O
server	O
and	O
Stack	B-Application
build	B-Application
tool	I-Application
were	O
made	O
in	O
response	O
to	O
these	O
criticisms	O
.	O
</s>
<s>
Cabal	B-Application
itself	O
now	O
has	O
a	O
much	O
more	O
sophisticated	O
build	B-Application
system	I-Application
,	O
heavily	O
inspired	O
by	O
Nix	B-Application
,	O
which	O
became	O
the	O
default	O
with	O
version	O
3.0	O
.	O
</s>
<s>
Clean	B-Operating_System
is	O
a	O
close	O
,	O
slightly	O
older	O
relative	O
of	O
Haskell	B-Language
.	O
</s>
<s>
Its	O
biggest	O
deviation	O
from	O
Haskell	B-Language
is	O
in	O
the	O
use	O
of	O
uniqueness	O
types	O
instead	O
of	O
monads	O
for	O
I/O	B-General_Concept
and	O
side-effects	O
.	O
</s>
<s>
A	O
series	O
of	O
languages	O
inspired	O
by	O
Haskell	B-Language
,	O
but	O
with	O
different	O
type	O
systems	O
,	O
have	O
been	O
developed	O
,	O
including	O
:	O
</s>
<s>
Agda	B-Language
,	O
a	O
functional	B-Language
language	I-Language
with	O
dependent	O
types	O
.	O
</s>
<s>
Elm	B-Language
,	O
a	O
functional	B-Language
language	I-Language
to	O
create	O
web	O
front-end	O
apps	O
,	O
no	O
support	O
for	O
user-defined	O
or	O
higher-kinded	O
type	O
classes	O
or	O
instances	O
.	O
</s>
<s>
Epigram	B-Language
,	O
a	O
functional	B-Language
language	I-Language
with	O
dependent	O
types	O
suitable	O
for	O
proving	O
properties	O
of	O
programs	O
.	O
</s>
<s>
Idris	B-Language
,	O
a	O
general	O
purpose	O
functional	B-Language
language	I-Language
with	O
dependent	O
types	O
,	O
developed	O
at	O
the	O
University	O
of	O
St	O
Andrews	O
.	O
</s>
<s>
PureScript	B-Language
compiles	B-Language
to	O
JavaScript	B-Language
.	O
</s>
<s>
Ωmega	B-Application
,	O
strict	O
and	O
more	O
.	O
</s>
<s>
Curry	B-Application
,	O
a	O
functional/logic	O
programming	O
language	O
based	O
on	O
Haskell	B-Language
.	O
</s>
<s>
Notable	O
Haskell	B-Language
variants	O
include	O
:	O
</s>
<s>
Generic	O
Haskell	B-Language
,	O
a	O
version	O
of	O
Haskell	B-Language
with	O
type	O
system	O
support	O
for	O
generic	B-Language
programming	I-Language
.	O
</s>
<s>
Hume	B-Language
,	O
a	O
strict	O
functional	B-Language
language	I-Language
for	O
embedded	B-Architecture
systems	I-Architecture
based	O
on	O
processes	O
as	O
stateless	O
automata	O
over	O
a	O
sort	O
of	O
tuples	O
of	O
one	O
element	O
mailbox	O
channels	O
where	O
the	O
state	O
is	O
kept	O
by	O
feedback	O
into	O
the	O
mailboxes	O
,	O
and	O
a	O
mapping	O
description	O
from	O
outputs	O
to	O
channels	O
as	O
box	O
wiring	O
,	O
with	O
a	O
Haskell-like	O
expression	O
language	O
and	O
syntax	O
.	O
</s>
<s>
The	O
Haskell	B-Language
community	O
meets	O
regularly	O
for	O
research	O
and	O
development	O
activities	O
.	O
</s>
