<s>
ISWIM	B-Language
(	O
acronym	O
for	O
If	B-Language
you	I-Language
See	I-Language
What	I-Language
I	I-Language
Mean	I-Language
)	O
is	O
an	O
abstract	O
computer	O
programming	O
language	O
(	O
or	O
a	O
family	O
of	O
languages	O
)	O
devised	O
by	O
Peter	O
Landin	O
and	O
first	O
described	O
in	O
his	O
article	O
"	O
The	B-Language
Next	I-Language
700	I-Language
Programming	I-Language
Languages	I-Language
"	O
,	O
published	O
in	O
the	O
Communications	O
of	O
the	O
ACM	O
in	O
1966	O
.	O
</s>
<s>
Although	O
not	O
implemented	O
,	O
it	O
has	O
proved	O
very	O
influential	O
in	O
the	O
development	O
of	O
programming	O
languages	O
,	O
especially	O
functional	B-Language
programming	I-Language
languages	I-Language
such	O
as	O
SASL	B-Language
,	O
Miranda	B-Language
,	O
ML	B-Language
,	O
Haskell	B-Language
and	O
their	O
successors	O
,	O
and	O
dataflow	B-Application
programming	I-Application
languages	I-Application
like	O
Lucid	B-Language
.	O
</s>
<s>
ISWIM	B-Language
is	O
an	O
imperative	B-Application
programming	I-Application
language	I-Application
with	O
a	O
functional	B-Language
core	O
,	O
consisting	O
of	O
a	O
syntactic	O
sugaring	O
of	O
lambda	B-Language
calculus	I-Language
to	O
which	O
are	O
added	O
mutable	O
variables	O
and	O
assignment	O
and	O
a	O
powerful	O
control	O
mechanism	O
:	O
the	O
program	O
point	O
operator	O
.	O
</s>
<s>
Being	O
based	O
on	O
lambda	B-Language
calculus	I-Language
,	O
ISWIM	B-Language
has	O
higher-order	B-Language
functions	I-Language
and	O
lexically	O
scoped	O
variables	O
.	O
</s>
<s>
The	O
operational	O
semantics	O
of	O
ISWIM	B-Language
are	O
defined	O
using	O
Landin	O
's	O
SECD	B-Application
machine	I-Application
and	O
use	O
call-by-value	O
,	O
that	O
is	O
eager	O
evaluation	O
.	O
</s>
<s>
A	O
goal	O
of	O
ISWIM	B-Language
was	O
to	O
look	O
more	O
like	O
mathematical	O
notation	O
,	O
so	O
Landin	O
abandoned	O
ALGOL	B-Language
's	O
semicolons	O
between	O
statements	O
and	O
begin	O
...	O
end	O
blocks	O
and	O
replaced	O
them	O
with	O
the	O
off-side	B-Language
rule	I-Language
and	O
scoping	O
based	O
on	O
indentation	O
.	O
</s>
<s>
A	O
notationally	O
distinctive	O
feature	O
of	O
ISWIM	B-Language
is	O
its	O
use	O
of	O
where	O
clauses	O
.	O
</s>
<s>
An	O
ISWIM	B-Language
program	O
is	O
a	O
single	O
expression	O
qualified	O
by	O
where	O
clauses	O
(	O
auxiliary	O
definitions	O
including	O
equations	O
among	O
variables	O
)	O
,	O
conditional	O
expressions	O
and	O
function	O
definitions	O
.	O
</s>
<s>
Along	O
with	O
CPL	B-Language
,	O
ISWIM	B-Language
was	O
one	O
of	O
the	O
first	O
programming	O
languages	O
to	O
use	O
where	O
clauses	O
.	O
</s>
<s>
This	O
was	O
done	O
using	O
a	O
somewhat	O
verbose	O
natural	O
language	O
style	O
description	O
,	O
but	O
apart	O
from	O
notation	O
amounts	O
exactly	O
to	O
the	O
algebraic	O
data	O
types	O
found	O
in	O
modern	O
functional	B-Language
languages	I-Language
.	O
</s>
<s>
ISWIM	B-Language
variables	O
did	O
not	O
have	O
explicit	O
type	O
declarations	O
and	O
it	O
seems	O
likely	O
(	O
although	O
not	O
explicitly	O
stated	O
in	O
the	O
1966	O
paper	O
)	O
that	O
Landin	O
intended	O
the	O
language	O
to	O
be	O
dynamically	O
typed	O
,	O
like	O
LISP	B-Language
and	O
unlike	O
ALGOL	B-Language
;	O
but	O
it	O
is	O
also	O
possible	O
that	O
he	O
intended	O
to	O
develop	O
some	O
form	O
of	O
type	O
inference	O
.	O
</s>
<s>
No	O
direct	O
implementation	O
of	O
ISWIM	B-Language
was	O
attempted	O
but	O
Art	O
Evan	O
's	O
language	O
PAL	B-Language
,	O
and	O
John	O
C	O
.	O
Reynolds	O
 '	O
language	O
Gedanken	O
,	O
captured	O
most	O
of	O
Landin	O
's	O
concepts	O
,	O
including	O
powerful	O
transfer-of-control	O
operations	O
.	O
</s>
<s>
Robin	O
Milner	O
's	O
ML	B-Language
may	O
be	O
considered	O
equivalent	O
to	O
ISWIM	B-Language
without	O
the	O
J	O
operator	O
and	O
with	O
type	O
inference	O
.	O
</s>
<s>
Another	O
line	O
of	O
descent	O
from	O
ISWIM	B-Language
is	O
to	O
strip	O
out	O
the	O
imperative	B-Application
features	O
(	O
assignment	O
and	O
the	O
J	O
operator	O
)	O
leaving	O
a	O
purely	O
functional	B-Language
language	I-Language
.	O
</s>
<s>
This	O
path	O
led	O
to	O
programming	O
languages	O
SASL	B-Language
,	O
Kent	B-Language
Recursive	I-Language
Calculator	I-Language
(	O
KRC	O
)	O
,	O
Hope	B-Language
,	O
Miranda	B-Language
,	O
Haskell	B-Language
,	O
and	O
Clean	B-Operating_System
.	O
</s>
