Function/ Macro to get a value - function

Question

Let say I have a table with 3 variable: var1, var2, var3 and another table of reference.
Now I want to create anothe variable: var4; var4 is computed from var1, var2 and var3 and the reference table.
I could create a macro to do that (for each line), but I dont know how to pass the value from the macro (a table) into a result. I wonder how can we do it by creating a function to get a value, not a macro?
I understand that if I can create a function like that (this function will include data step and proc summary), thing will be easy like:
var4 = myfunction(var1, var2, var3).
Update:
The table reference in my case is:
age range1 range2 range3
1 10 1 8
2 0 4 1
3 4 6 1
4 6 5 2
5 10 5 6
So I want my function to get like:
var4 = myfunction(var1, var2, var3), for example var1 = 2, var2 = 2, var3 = 5:
Take the sum of range2 (correspond to var1 = 2); from line 2 to line 5 (corrspond to var2= 2 and var3 = 5) and the result will be: 4 + 6 + 5 + 5.
Thanks in advance.

Answer 1

One solution could be to first modify the reference table to a long format with one row per age per range number, and with the accumulated range in a new variable. The sum from var2 to var3 then becomes the difference between two accumulated values, which is easier to compute in a double join:
* Define input data with parameters;
data have;
input var1 var2 var3;
datalines;
1 1 3
2 2 5
3 1 4
;
run;
* Define reference table;
data ref_table;
input age range1 range2 range3;
datalines;
1 10 1 8
2 0 4 1
3 4 6 1
4 6 5 2
5 10 5 6
;
run;
* Modify reference table to long format with accumulated ranges;
data mod_ref_table;
set ref_table;
* Calculated accumulated values of each range;
acc_range1 + range1;
acc_range2 + range2;
acc_range3 + range3;
* Output the accumulated values for each range;
range_no = 1;
acc_range = acc_range1;
output;
range_no = 2;
acc_range = acc_range2;
output;
range_no = 3;
acc_range = acc_range3;
output;
keep age range_no acc_range;
run;
* Calculate output;
proc sql;
create table want as
select a.*
,case
when a.var2 = 1 then c.acc_range
else c.acc_range - b.acc_range
end as val4
from have as a
left join mod_ref_table as b
on a.var1 = b.range_no and a.var2-1 = b.age
left join mod_ref_table as c
on a.var1 = c.range_no and a.var3 = c.age
;
quit;

Answer 2

Macro returning a value
OK the solution can be found here.
Anyway thanks for your support.