Nested Do Loops in SAS - loops

Question

I'm trying to figure out how to nest these loops so that I can generate some multilevel data. I keep getting an error, though. I'm really new to SAS so I'm struggling to figure out how to fix this. Thanks for any help!
%macro MLM;
data x;
call streaminit(525600);
do rep=1 to 1000;
%do a=1 %to 4;
%if &a=1 %then %do; %let N=100; %end;
%if &a=2 %then %do; %let N=250; %end;
%if &a=3 %then %do; %let N=500; %end;
%if &a=4 %then %do; %let N=1000; %end;
do J=1 to &N;
u0= RAND('NORMAL',0,1);
w1= RAND('BERNOULLI',.5);
do I=1 to (10000/&N);
%do b = 1 %to 5;
%if &b=1 %then %do; %let e=RAND('NORMAL',0,1); %end;
%if &b=2 %then %do; %let e=RAND('UNIFORM'); %end;
%if &b=3 %then %do; %let e=RAND('CHISQUARE', &N-1); %end;
%if &b=4 %then %do; %let e=RAND('LOGNORMAL'); %end;
%if &b=5 %then %do; %let e=RAND('BETA',1,1); %end;
x1= RAND('BERNOULLI',.5);
b0 = 2.5+ 1*w1+u0;
b1 = 0.15;
y=b0+b1*x1+&e;
output;
%end;
end;
end;
%end;
end;
%mend MLM; run; %MLM; run;
I want to run 1000 simulations, with 4 sample sizes (a, N), then generate N samples, during which I want to simulate 5 different error distributions. So, in the end, I should get 1000x4x5 total samples.
Thanks again!

Answer 1

Removing the macro logic and simplifying it slightly gets you this, which seems to work correctly to me. Note I simplified the N to ensure it runs quickly. Note that I'm not verify the logic, assuming that's correct on your side.
data x;
call streaminit(525600);
do rep=1 to 5;
do a=1 to 4;
if a=1 then
N=100;
else if a=2 then
N=250;
else if a=3 then
N=500;
else if a=4 then
N=1000;
do J=1 to N;
u0=RAND('NORMAL', 0, 1);
w1=RAND('BERNOULLI', .5);
do I=1 to (2000/N);
do b=1 to 5;
if b=1 then
e=RAND('NORMAL', 0, 1);
else if b=2 then
e=RAND('UNIFORM');
else if b=3 then
e=RAND('CHISQUARE', N-1);
else if b=4 then
e=RAND('LOGNORMAL');
else if b=5 then
e=RAND('BETA', 1, 1);
x1=RAND('BERNOULLI', .5);
b0=2.5+ 1*w1+u0;
b1=0.15;
y=b0+b1*x1+e;
output;
end;
end;
end;
end;
end;
run;