<s>
Fril	B-Language
is	O
a	O
programming	O
language	O
for	O
first-order	O
predicate	O
calculus	O
.	O
</s>
<s>
It	O
includes	O
the	O
semantics	B-Application
of	O
Prolog	B-Language
as	O
a	O
subset	O
,	O
but	O
takes	O
its	O
syntax	O
from	O
the	O
of	O
Logic	B-Language
Programming	I-Language
Associates	O
and	O
adds	O
support	O
for	O
fuzzy	O
sets	O
,	O
support	O
logic	O
,	O
and	O
metaprogramming	B-Application
.	O
</s>
<s>
Fril	B-Language
was	O
originally	O
developed	O
by	O
Trevor	B-Language
Martin	I-Language
and	O
Jim	O
Baldwin	O
at	O
the	O
University	O
of	O
Bristol	O
around	O
1980	O
.	O
</s>
<s>
Research	O
,	O
which	O
later	O
became	O
Fril	B-Language
Systems	O
Ltd	O
.	O
</s>
<s>
The	O
name	O
Fril	B-Language
was	O
originally	O
an	O
acronym	O
for	O
Fuzzy	B-Language
Relational	I-Language
Inference	I-Language
Language	I-Language
.	O
</s>
<s>
Aside	O
from	O
the	O
uncertainty-management	O
features	O
of	O
Fril	B-Language
,	O
there	O
are	O
some	O
minor	O
differences	O
in	O
Fril	B-Language
's	O
implementation	O
of	O
standard	O
Prolog	B-Language
features	O
.	O
</s>
<s>
The	O
basic	O
types	O
in	O
Fril	B-Language
are	O
similar	O
to	O
those	O
in	O
Prolog	B-Language
,	O
with	O
one	O
important	O
exception	O
:	O
Prolog	B-Language
's	O
compound	O
data	O
type	O
is	O
the	O
term	O
,	O
with	O
lists	O
defined	O
as	O
nested	O
terms	O
using	O
the	O
.	O
</s>
<s>
functor	O
;	O
in	O
Fril	B-Language
,	O
the	O
compound	O
type	O
is	O
the	O
list	O
itself	O
,	O
which	O
forms	O
the	O
basis	O
for	O
most	O
constructs	O
.	O
</s>
<s>
Variables	O
are	O
distinguished	O
by	O
identifiers	O
containing	O
only	O
uppercase	O
letters	O
and	O
underscores	O
(	O
whereas	O
Prolog	B-Language
only	O
requires	O
the	O
first	O
character	O
to	O
be	O
uppercase	O
)	O
.	O
</s>
<s>
As	O
in	O
Prolog	B-Language
,	O
the	O
name	O
_	O
is	O
reserved	O
to	O
mean	O
"	O
any	O
value	O
"	O
,	O
with	O
multiple	O
occurrences	O
of	O
_	O
replaced	O
by	O
distinct	O
variables	O
.	O
</s>
<s>
Prolog	B-Language
has	O
a	O
syntax	O
with	O
a	O
typical	O
amount	O
of	O
punctuation	O
,	O
whereas	O
Fril	B-Language
has	O
an	O
extremely	O
simple	O
syntax	O
similar	O
to	O
that	O
of	O
Lisp	B-Language
.	O
</s>
<s>
These	O
are	O
equivalent	O
to	O
the	O
respective	O
Prolog	B-Language
constructions	O
:	O
</s>
<s>
For	O
example	O
,	O
consider	O
the	O
member	O
predicate	O
in	O
Prolog	B-Language
:	O
</s>
<s>
In	O
Fril	B-Language
,	O
this	O
becomes	O
:	O
</s>
<s>
Fril	B-Language
supports	O
both	O
continuous	O
and	O
discrete	O
fuzzy	O
sets	O
,	O
each	O
with	O
their	O
own	O
special	O
syntaxes	O
.	O
</s>
<s>
Fril	B-Language
has	O
predicates	O
for	O
fuzzy	O
set	O
operations	O
(	O
but	O
does	O
not	O
directly	O
support	O
control	O
through	O
fuzzy	O
logic	O
)	O
.	O
</s>
<s>
Fril	B-Language
includes	O
predicates	O
that	O
calculate	O
the	O
support	O
for	O
a	O
given	O
query	O
.	O
</s>
<s>
While	O
Prolog	B-Language
uses	O
punctuation	O
namely	O
;	O
for	O
disjunction	O
within	O
clauses	O
,	O
Fril	B-Language
instead	O
has	O
a	O
built-in	O
predicate	O
orr	O
.	O
</s>
<s>
On	O
the	O
positive	O
side	O
,	O
it	O
renders	O
predicates	O
such	O
as	O
Prolog	B-Language
's	O
=	O
..	O
(	O
which	O
maps	O
between	O
lists	O
and	O
clauses	O
)	O
unnecessary	O
,	O
as	O
a	O
clause	O
is	O
a	O
list	O
.	O
</s>
<s>
As	O
a	O
logic	B-Language
programming	I-Language
environment	O
,	O
Fril	B-Language
is	O
very	O
similar	O
to	O
Prolog	B-Language
.	O
</s>
<s>
Both	O
Prolog	B-Language
and	O
Fril	B-Language
have	O
shell	B-Operating_System
applications	O
,	O
which	O
serve	O
as	O
the	O
standard	O
way	O
of	O
interacting	O
with	O
them	O
.	O
</s>
<s>
Prolog	B-Language
reads	O
commands	O
in	O
two	O
modes	O
:	O
in	O
source	O
file-reading	O
mode	O
,	O
it	O
accepts	O
directives	O
and	O
clauses	O
;	O
in	O
user	O
interaction	O
mode	O
,	O
it	O
accepts	O
only	O
queries	O
(	O
although	O
it	O
is	O
possible	O
to	O
tell	O
Prolog	B-Language
to	O
read	O
directives	O
and	O
clauses	O
from	O
standard	O
input	O
by	O
using	O
consult(user )	O
.	O
)	O
.	O
</s>
<s>
Fril	B-Language
makes	O
no	O
distinction	O
:	O
all	O
types	O
of	O
commands	O
can	O
be	O
given	O
both	O
from	O
source	O
files	O
and	O
on	O
the	O
command	O
line	O
.	O
</s>
<s>
The	O
Prolog	B-Language
shell	B-Operating_System
automatically	O
prints	O
the	O
values	O
of	O
all	O
instantiated	O
variables	O
that	O
appear	O
in	O
a	O
query	O
,	O
along	O
with	O
a	O
yes	O
or	O
no	O
answer	O
.	O
</s>
<s>
The	O
Fril	B-Language
shell	B-Operating_System
only	O
gives	O
the	O
answer	O
;	O
it	O
is	O
the	O
user	O
's	O
responsibility	O
to	O
print	O
variables	O
if	O
desired	O
.	O
</s>
