Let

The let construct in Clojure allows local variables to be defined and initialized.

(let [ var₁ init₁ ... ] code )

(let [ d (* 2.0 r)
       c (* Math/PI d) ]   ... )

Each variable is initialized with the value of the corresponding initialization code; these initialization steps are executed in order, so the result of one can be used in later init code.[This is called let* is some Lisp dialects.]

let is useful to save the result of a (possibly expensive) function call so that it can be used multiple times without having to be recomputed.

There can be multiple forms inside the let; the value of the let is the value of the last form.

(defn lookupstudent [eid]
  (let [idname (assocl eid alist)]
    (if idname
        (second idname)
        "John Doe") ) )