Editing Oz (programming language) (section)

===Functions===
Functions<ref name="Advanced Functional Programming in Oz">{{cite book
| author = Leif Grönqvist
| title = Advanced Functional Programming in Oz
| chapter = Higher Order Functions
| url = http://www2.gslt.hum.gu.se/~leifg/gslt/doc/ozfunpaper.ps
| access-date = 3 November 2014
| archive-url = https://web.archive.org/web/20160303171453/http://www2.gslt.hum.gu.se/~leifg/gslt/doc/ozfunpaper.ps
| archive-date = 3 March 2016
| url-status = dead
}}</ref> are first class values, allowing [[Higher-order programming|higher order functional]] programming:
<syntaxhighlight lang="erlang">
fun {Fact N}
   if N =< 0 then 1 else N*{Fact N-1} end
end
</syntaxhighlight><syntaxhighlight lang="erlang">
fun {Comb N K}
   {Fact N} div ({Fact K} * {Fact N-K}) % integers can't overflow in Oz (unless no memory is left)
end

fun {SumList List}
   case List of nil then 0
   [] H|T then H+{SumList T} % pattern matching on lists
   end
end
</syntaxhighlight>
Functions may be used with both free and bound variables. Free variable values are found using static [[Scope (computer science)|lexical scoping]].<ref name="Scoping">
{{cite journal
| author = Robert Gentleman|author2=Ross Ihaka
| title = Lexical Scope in Statistical Computing
| url= https://www.stat.auckland.ac.nz/~ihaka/downloads/lexical.pdf
|journal=Journal of Computational and Graphical Statistics
|volume= 9|issue= 3, Systems and Languages |date=Sep 2000|pages=491–508|doi=10.1080/10618600.2000.10474895
}}
</ref>

====Higher-order programming====
Functions are like other Oz objects. A function can be passed as an attribute to other functions or can be returned in a function. 
<syntaxhighlight lang="erlang">
fun {Square N}  % A general function
   N*N
end

fun {Map F Xs}  % F is a function here - higher order programming
   case Xs
      of nil then nil
      [] X|Xr then {F X}|{Map F Xr}
   end
end

%usage
{Browse {Map Square [1 2 3]}}  %browses [1 4 9] 
</syntaxhighlight>

====Anonymous functions====
Like many other functional languages, Oz supports use of [[anonymous function]]s (i.e. functions which do not have a name) with higher order programming.  The symbol $ is used to denote these.

In the following, the square function is defined anonymously and passed, causing <code>[1 4 9]</code> to be browsed.
<syntaxhighlight lang="erlang">
{Browse {Map fun {$ N} N*N end [1 2 3]}} 
</syntaxhighlight>

Since anonymous functions don't have names, it is not possible to define recursive anonymous functions.

====Procedures====
Functions in Oz are supposed to return a value at the last statement encountered in the body of the function during its execution. In the example below, the function Ret returns 5 if X > 0 and -5 otherwise.
<syntaxhighlight lang="erlang">
declare
fun {Ret X}
   if X > 0 then 5 else ~5 end
end
</syntaxhighlight>
But Oz also provides a facility in case a function must not return values. Such functions are called procedures.<ref>{{Cite web|url=https://mozart.github.io/mozart-v1/doc-1.4.0/tutorial/node5.html#control.procedure|title = 5 Basic Control Structures}}</ref> Procedures are defined using the construct "proc" as follows
<syntaxhighlight lang="erlang">
declare
proc {Ret X}
   if X > 0 then {Browse 5} else {Browse ~5} end
end
</syntaxhighlight>
The above example doesn't return any value, it just prints 5 or -5 in the Oz browser depending on the sign of X.