124  Pascal User Manual  11.B.1.  Functional parameters  Produces as results:  begin  Pi  := ArcTan(1.0)  *  ,  Write1n(Output,  2.0  :11:(.  7  :3,  Power(2.0,7)  :11:6);  PiSquared := Power(Pi,2);  Write1n(Output,  Pi  :11:E,  2  :3,  PiSquared  Writeln(Output,  PiSquared  :11:6,  2  :3,  : 11: 6) ;  Power (PiSquared,  2)  :11:6);  Writeln(Output,  Pi  :11:6,  4  :3,  Power(Pi,4)  :11:6)  end { Exponentiation2  } .  Functions themselves may also be passed as parameters to procedures  and functions. A formal functional parameter is specified by a function  heading; its corresponding actual parameter is a function identifier.  Program 11.9 computes the sum of terms in a series  for different  functions specified at activation.  program SumSeries(Output);  { Program 11.9 - Write a  table of a  series sum  progress: ,m.  }  const  MaxTerms  =  10;  var  Term:  1 .. MaxTerms;  function Sigma (  function r,:X:Real):Real;  Lower,:pper  :Integer ): Real;  var  Index:  Integer;  Sum:  Real;  begin  Sum  := 0.0;  for Index  :  =  Lower to UFT'er do  Sum  := Sum + F(Index);  Sigma  := Sum  end { Sigma };  2.000000  7  128.000000  3.141593  2  9.869605  9.869605  2  97.409100  3.141593  4  97.409100 