Editing Scope (computer science) (section)

=== Lisp ===
[[Lisp (programming language)|Lisp]] dialects have various rules for scope.

The original Lisp used dynamic scope; it was [[Scheme (programming language)|Scheme]], inspired by [[ALGOL]], that introduced static (lexical) scope to the Lisp family.

[[Maclisp]] used dynamic scope by default in the interpreter and lexical scope by default in compiled code, though compiled code could access dynamic bindings by use of <code>SPECIAL</code> declarations for particular variables.<ref>{{cite web |url=http://maclisp.info/pitmanual/complr.html#23.1.2 |title=The Revised Maclisp Manual (The Pitmanual), Sunday Morning Edition |last=Pitman |first=Kent |date=December 16, 2007 |website=MACLISP.info |publisher=HyperMeta Inc. |access-date=October 20, 2018|at=Declarations and the Compiler, Concept "Variables" |quote= If the variable to be bound has been declared to be special, the binding is compiled as code to imitate the way the interpreter binds variables }}</ref> However, [[Maclisp]] treated lexical binding more as an optimization than one would expect in modern languages, and it did not come with the [[Closure (computer programming)|closure]] feature one might expect of lexical scope in modern Lisps. A separate operation, <code>*FUNCTION</code>, was available to somewhat clumsily work around some of that issue.<ref>{{cite web |url=http://www.maclisp.info/pitmanual/eval.html#3.7.1 |title=The Revised Maclisp Manual (The Pitmanual), Sunday Morning Edition |last=Pitman |first=Kent |date=December 16, 2007 |website=MACLISP.info |publisher=HyperMeta Inc. |access-date=October 20, 2018|at=The Evaluator, Special Form <code>*FUNCTION</code> |quote= <code>*FUNCTION</code> is intended to help solve the "[[funarg problem]]," however it only works in some easy cases. }}</ref>

[[Common Lisp]] adopted lexical scope from [[Scheme (programming language)|Scheme]],<ref>{{cite web |url=http://www.lispworks.com/documentation/lw50/CLHS/Body/01_ab.htm |title=Common Lisp HyperSpec |last=Pitman |first=Kent |collaboration=webbed version of ANSI standard X3.226-1994 |date=1996 |website=Lispworks.com |publisher=LispWorks Ltd. |access-date=October 20, 2018|at=1.1.2 History |quote=MacLisp improved on the Lisp 1.5 notion of special variables ... The primary influences on Common Lisp were Lisp Machine Lisp, MacLisp, NIL, S-1 Lisp, Spice Lisp, and Scheme. }}</ref> as did [[Clojure]].

[[ISLISP]] has lexical scope for ordinary variables. It also has dynamic variables, but they are in all cases explicitly marked; they must be defined by a <code>defdynamic</code> special form, bound by a <code>dynamic-let</code> special form, and accessed by an explicit <code>dynamic</code> special form.<ref>{{cite web |url=http://www.islisp.info/Documents/PDF/islisp-2007-03-17-pd-v23.pdf |title=Programming Language ISLISP, ISLISP Working Draft 23.0|website=ISLISP.info |access-date=October 20, 2018 |at=11.1 The lexical principle |quote= Dynamic bindings are established and accessed by a separate mechanism (i.e., <code>defdynamic</code>, <code>dynamic-let</code>, and <code>dynamic</code>).}}</ref>

Some other dialects of Lisp, like [[Emacs Lisp]], still use dynamic scope by default. Emacs Lisp now has lexical scope available on a per-buffer basis.<ref name=":0">{{cite web |url=https://www.emacswiki.org/emacs/LexicalBinding |title=Lexical Binding |website=EmacsWiki |access-date=October 20, 2018 |quote=Emacs 24 has optional lexical binding, which can be enabled on a per-buffer basis. }}</ref>