for循环中的vhdl错误。 Erro 10500

Question

我在vhdl中做了一个简单的ula。在sum操作中得到消息错误

错误：

Error (10500): VHDL syntax error at rjr_neander.vhd(30) near text "for";  expecting "end", or "(", or an identifier ("for" is a reserved keyword), or a concurrent statement
Error (10500): VHDL syntax error at rjr_neander.vhd(34) near text "loop";  expecting ";", or an identifier ("loop" is a reserved keyword), or "architecture"

代码：

entity ula is
port(
        inputA, inputB: in bit_vector(0 to 7);
        output: out bit_vector(0 to 7)
        );
end ula;  


architecture sum8bits of ula is
        signal cout : bit_vector(0 to 6);
begin 
        -- Half adder do bit 0
        output(0) <= inputA(0) xor inputB(0);
        cout(0) <= inputA(0) and inputB(0);
        for indice in 1 to 7 loop
        -- iteracao para fazer o full adder dos 7 bits restantes
            output(indice) <= inputA(indice) xor inputB(indice) xor cout(indice-1);
            cout(indice) <= (inputA(indice) and inputB(indice)) or (inputA(indice) and cout(indice-1)) or (inputB(indice) and cout(indice-1));
        end loop;
end sum8bits;

我的错误是什么？