ISWIM
(If You See What I Mean ) An influential but
unimplemented computer programming language described in the
article by {Peter J . Landin } cited below . Landin attempted to
capture all known programming language concepts , including
assignment } and control operators such as {goto } and
coroutines }, within a single {lambda calculus } based
framework .
ISWIM is an {imperative language } with a functional core ,
consisting of {sugared } {lambda calculus } plus {mutable
variables } and {assignment }. A powerful control mechanism ,
Landin 's {J operator }, enables capture of the current
continuation } (the {call /cc } operator of {Scheme } is a
simplified version ). Being based on lambda calculus ISWIM had
higher order functions } and {lexically scoped } variables .
The {operational semantics } of ISWIM are defined using
Landin 's {SECD machine } and use {call -by -value } ({eager
evaluation }). To make ISWIM look more like mathematical
notation , Landin replaced {ALGOL }'s semicolons and begin end
blocks with the {off -side rule } and scoping based on
indentation .
An ISWIM program is a single {expression } qualified by "where "
clauses (auxiliary definitions including equations among
variables ), conditional expressions and function definitions .
With {CPL }, ISWIM was one of the first programming languages
to use "where " clauses .
New {data types } could be defined as a (possibly recursive )
sum of products } like the {algebraic data types } found in
modern functional languages . ISWIM variables were probably
dynamically typed } but Landin may have planned some form of
type inference }.
Concepts from ISWIM appear in Art Evan 's {PAL } and John
Reynold 's {Gedanken }, Milner 's {ML } and purely functional
languages with lazy evaluation like {SASL }, {Miranda } and
Haskell }.
The Next 700 Programming Languages "
http ://www .cs .utah .edu /~wilson /compilers /old /papers /p157 -landin .pdf )},
P .J . Landin , CACM 9 (3 ):157 -166 , Mar 1966 ].
2007 -03 -20 )
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