I would like to ask about how can I mesh my semicircle domain

Border c(t=0,2*pi) {x=cos(t);y=sin(t); label =1;};

The code above is for a circle, and I want a semicircle. I changed it t=0, pi But it didn’t work

I would like to ask about how can I mesh my semicircle domain

Border c(t=0,2*pi) {x=cos(t);y=sin(t); label =1;};

The code above is for a circle, and I want a semicircle. I changed it t=0, pi But it didn’t work