" should be a lambda expression" error?

(defun manhatten-distance (state)
           (let ((index 0)
                 (total 0)
                 (current 0)
                 (cvalue 0)
                 (rvalue 0))
                 (loop for i from 0 to 8 do
                       ((setf current (nth i state))))))

SYSTEM::%EXPAND-FORM: (SETF CURRENT (NTH I STATE)) should be a lambda expression
   [Condition of type SYSTEM::SIMPLE-SOURCE-PROGRAM-ERROR]

Why am I getting this error?

I found it. I have one too many parenthesis after do.

The thing is, shouldn't I put the sequence of functions into one s-expression block like let does?

yougene wrote:The thing is, shouldn't I put the sequence of functions into one s-expression block like let does?

What do you mean? LET doesn't put the code to be executed into one s-expression. All parentheses in Lisp are meaningful, you shouldn't be putting them at random. All standard operators have a clearly defined grammar, although the one for LOOP is admittedly really long.

yougene wrote:The thing is, shouldn't I put the sequence of functions into one s-expression block like let does?

The extra parenthesis in let is only around the variables to be declared, not around the forms to be executed.

Brainfart