Euler Method Recursive Calc for HP Prime

SUBCALC(); // DECLARE SUBROUTINE

EXPORT euler_cl(k,z,step_size,goal) //k is xn-1, z is yn-1
BEGIN
LOCAL x0:=k, y0:=z;

k := x0+step_size; //xn= xn-1 + h
z := y0+step_size*SUBCALC(x0,y0);//yn = yn-1 +h*f(xn-1,yn-1)

//Print steps
print("Xn="+k);
print ("Yn="+z);

IF k =goal THEN
 print("The answer is:"+z);
 return z;
ELSE
 euler_cl(k,z,step_size,goal);
END;
END;

SUBCALC(X,Y) //Subroutine for f(x,y) function
BEGIN
RETURN 1+2*X-3*Y; // EDIT HERE TO CHANGE FUNCTION
END;