/*  Create a SAS function called "LN" in FCMP and store it in a SAS catalog, where  */
/*  outlib=library.catalog.package specifies where the SAS function will be stored  */
proc fcmp outlib = sasuser.FCMP_Cat.fcns; 
  /*  Example of a SAS function definition for the natural log  */
  function ln(x);
    y = log(x);
    return(y);
  endsub;
quit; 


/*  Let SAS know about the "FCMP_Cat" catalog  */
options cmplib=(sasuser.FCMP_Cat);


/*  Test a call of the LN function using PROC FCMP  */
proc fcmp;   
  /*  Example of calling SAS function "LN" */
  out = ln(10);
  /*  Print result to output listing  */
  put "Testing Function Call";
  put "LN(10) returns:" out;
quit;


/*  Generate synthetic data to be used in PROC MODEL  */
data logdata;
  a = 0.5;
  do x=1 to 10000;
    z = rannor(123);
    y = log(a*x) + z;
    output;
  end;
run;


/*  Utilize the "LN" function to estimate the parameter "a" with PROC MODEL  */
proc model data = logdata;
  parameters a;
  y = ln(a*x);
  fit y;
run;
quit;

http://support.sas.com/kb/26/151.html

Proc FCMP Example

SAS