Editing Computer program (section)

====Lisp====
[[Lisp (programming language)|Lisp]] (1958) stands for "LISt Processor".<ref name="ArtOfLisp">{{cite book
 | last1=Jones
 | first1=Robin
 | last2=Maynard
 | first2=Clive
 | last3=Stewart
 | first3=Ian
 | title=The Art of Lisp Programming
 | date=December 6, 2012
 | publisher=Springer Science & Business Media
 | isbn=9781447117193
 | page=2}}</ref> It is tailored to process [[List (abstract data type)|lists]]. A full structure of the data is formed by building lists of lists. In memory, a [[tree data structure]] is built. Internally, the tree structure lends nicely for [[Recursion (computer science)|recursive]] functions.<ref name="cpl_3rd-ch9-220">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 220
  | isbn = 0-201-71012-9
}}</ref> The syntax to build a tree is to enclose the space-separated [[Element (mathematics)|elements]] within parenthesis. The following is a [[list]] of three elements. The first two elements are themselves lists of two elements:

<code>((A B) (HELLO WORLD) 94)</code>

Lisp has functions to extract and reconstruct elements.<ref name="cpl_3rd-ch9-221">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 221
  | isbn = 0-201-71012-9
}}</ref> The function <code>head()</code> returns a list containing the first element in the list. The function <code>tail()</code> returns a list containing everything but the first element. The function <code>cons()</code> returns a list that is the concatenation of other lists. Therefore, the following expression will return the list <code>x</code>:

<code>cons(head(x), tail(x))</code>

One drawback of Lisp is when many functions are nested, the parentheses may look confusing.<ref name="cpl_3rd-ch9-230"/> Modern Lisp [[Integrated development environment|environments]] help ensure parenthesis match. As an aside, Lisp does support the ''imperative language'' operations of the assignment statement and goto loops.<ref name="cpl_3rd-ch9-229">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 229
  | isbn = 0-201-71012-9
}}</ref> Also, ''Lisp'' is not concerned with the [[datatype]] of the elements at compile time.<ref name="cpl_3rd-ch9-227">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 227
  | isbn = 0-201-71012-9
}}</ref> Instead, it assigns (and may reassign) the datatypes at [[Runtime (program lifecycle phase)|runtime]]. Assigning the datatype at runtime is called [[Name binding#Binding time|dynamic binding]].<ref name="cpl_3rd-ch9-222">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 222
  | isbn = 0-201-71012-9
}}</ref> Whereas dynamic binding increases the language's flexibility, programming errors may linger until late in the [[software development process]].<ref name="cpl_3rd-ch9-222"/>

Writing large, reliable, and readable Lisp programs requires forethought. If properly planned, the program may be much shorter than an equivalent ''imperative language'' program.<ref name="cpl_3rd-ch9-230"/> ''Lisp'' is widely used in [[artificial intelligence]]. However, its usage has been accepted only because it has ''imperative language'' operations, making unintended side-effects possible.<ref name="cpl_3rd-ch9-241"/>