Editing Nested function (section)

=== Simple example ===

A simple example in Pascal:
<syntaxhighlight lang=pascal>
function E(x: real): real;
    function F(y: real): real;
    begin
        F := x + y
    end;
begin
    E := F(3) + F(4)
end;
</syntaxhighlight>
The function <code>F</code> is nested within <code>E</code>. Note that <code>E</code>'s parameter <code>x</code> is also visible in <code>F</code> (as <code>F</code> is a part of <code>E</code>) while both <code>x</code> and <code>y</code> are invisible outside <code>E</code> and <code>F</code> respectively.

Similarly, in [[Standard ML]]:

<syntaxhighlight lang=ocaml>
fun e (x : real) =
  let
    fun f y = x+y
  in
    f 3 + f 4
  end;
</syntaxhighlight>

In [[Haskell (programming language)|Haskell]]:

<syntaxhighlight lang=haskell>
e :: Float -> Float
e x = f 3 + f 4 where f y = x + y
</syntaxhighlight>

In [[PL/I]]:

{{pre|
e: procedure(x) returns(float);
  declare x float;
  f: procedure(y) returns(float);
    declare y float;
    return x + y
    end;
  return f(3.0) + f(4.0);
  end;
}}

In [[Python (programming language)|Python]]:

<syntaxhighlight lang=python>
def e(x: float) -> float:
    def f(y: float) -> float:
        return x + y
    return f(3.0) + f(4.0)
</syntaxhighlight>

In [[GNU Compiler Collection|GNU C]]<ref>{{cite book |last1=Rothwell |first1=Trevis J. |title=The GNU C Reference Manual |date=2011 |publisher=Free Software Foundation, Inc |page=63}}</ref> {{endash}} which extends standard C with nested functions:

<syntaxhighlight lang=c>
float E(float x)
{
    float F(float y)
    {
        return x + y;
    }
    return F(3) + F(4);
}
</syntaxhighlight>