Interpreting SAS codes

[Budu]

As a neophyte, I am trying to find out what the codes, given below, are trying to achieve. I would appreciate if you could explain the following codes in plain English. Thanks.

Note: I understand the first set of codes, which basically get the data.

proc sql noprint;
    create table rates as
    select date, days, rate
    from optionm.zerocd;
quit;

proc expand data=rates out=rates_expanded from=daily;
    by date;
    id days;
    convert rate;
run;

data RiskFree;
    set rates_expanded;
    by date;
    if FIRST.date then do;
      do days = 1 to days;
        output;
      end;
    end;
    else output;
run;

[Peter_C]

might be better to ask the person who gave you the code

[LinusH]

Or try the program on some data.
Potentially using the data step debugger.