The “simple” loop form:

    loop {compound-form}* {result}*

    The “extended” loop form:

    loop [↓name-clause] {↓variable-clause}* {↓main-clause}* {result}*

    name-clause::= named name
    variable-clause::= with-clause | initial-final | for-as-clause
    with-clause::= with var1 [type-spec] [= form1] {and var2 [type-spec] [= form2]}*
    main-clause::= unconditional | accumulation | conditional | termination-test | initial-final
    initial-final::= initially {compound-form}+ | finally {compound-form}+
    unconditional::= {do | doing} {compound-form}+ | return {form | it}
    accumulation::= list-accumulation | numeric-accumulation
    list-accumulation::= {collect | collecting | append | appending | nconc | nconcing} {form | it}
    [into simple-var]
    numeric-accumulation::= {count | counting | sum | summing |
    maximize | maximizing | minimize | minimizing} {form | it}
    [into simple-var] [type-spec]
    conditional::= {if | when | unless} form selectable-clause {and selectable-clause}*
    [else selectable-clause {and selectable-clause}*]
    selectable-clause::= unconditional | accumulation | conditional
    termination-test::= while form | until form | repeat form | always form | never form | thereis form
    for-as-clause::= {for | as} for-as-subclause {and for-as-subclause}*
    for-as-subclause::= for-as-arithmetic | for-as-in-list | for-as-on-list | for-as-equals-then |
    for-as-across | for-as-hash | for-as-package
    for-as-arithmetic::= var [type-spec] for-as-arithmetic-subclause
    for-as-arithmetic-subclause::= arithmetic-up | arithmetic-downto | arithmetic-downfrom
    arithmetic-up::= ⟦ {from | upfrom} form1 | {to | upto | below} form2 | by form3 ⟧+
    arithmetic-downto::= ⟦ {from form1}1 | {{downto | above} form2}1 | by form3 ⟧
    arithmetic-downfrom::= ⟦ {downfrom form1}1 | {to | downto | above} form2 | by form3 ⟧
    for-as-in-list::= var [type-spec] in form1 [by step-fun]
    for-as-on-list::= var [type-spec] on form1 [by step-fun]
    for-as-equals-then::= var [type-spec] = form1 [then form2]
    for-as-across::= var [type-spec] across vector
    for-as-hash::= var [type-spec] being {each | the}
    {{hash-key | hash-keys} {in | of} hash-table
    [using (hash-value other-var)] |
    {hash-value | hash-values} {in | of} hash-table
    [using (hash-key other-var)]}
    for-as-package::= var [type-spec] being {each | the}
    {symbol | symbols |
    present-symbol | present-symbols |
    external-symbol | external-symbols}
    [{in | of} package]
    type-spec::= simple-type-spec | destructured-type-spec
    simple-type-spec::= fixnum | float | t | nil
    destructured-type-spec::= of-type d-type-spec
    d-type-spec::= type-specifier | (d-type-spec . d-type-spec)
    var::= d-var-spec
    var1::= d-var-spec
    var2::= d-var-spec
    other-var::= d-var-spec
    d-var-spec::= simple-var | nil | (d-var-spec . d-var-spec)
    Arguments and Values

    compound-form — a compound form.

    name — a symbol.

    simple-var — a symbol (a variable name).

    form, form1, form2, form3 — a form.

    step-fun — a form that evaluates to a function of one argument.

    vector — a form that evaluates to a vector.

    hash-table — a form that evaluates to a hash table.

    package — a form that evaluates to a package designator.

    type-specifier — a type specifier. This might be either an atomic type specifier or a compound type specifier, which introduces some additional complications to proper parsing in the face of destructuring; for further information, see Section (Destructuring).

    result — an object.


    For details, see Section 6.1 (The LOOP Facility).

    ;; An example of the simple form of LOOP. 
     (defun sqrt-advisor () 
       (loop (format t "~&Number: ") 
             (let ((n (parse-integer (read-line) :junk-allowed t))) 
               (when (not n) (return)) 
               (format t "~&The square root of ~D is ~D.~%" n (sqrt n))))) 
     Number: 5 
     The square root of 5 is 2.236068. 
     Number: 4 
     The square root of 4 is 2. 
     Number: done 
    ;; An example of the extended form of LOOP. 
     (defun square-advisor () 
       (loop as n = (progn (format t "~&Number: ") 
                           (parse-integer (read-line) :junk-allowed t)) 
             while n 
             do (format t "~&The square of ~D is ~D.~%" n (* n n)))) 
     Number: 4 
     The square of 4 is 16. 
     Number: 23 
     The square of 23 is 529. 
     Number: done 
    ;; Another example of the extended form of LOOP. 
     (loop for n from 1 to 10 
           when (oddp n) 
             collect n) 
     (1 3 5 7 9)
    See Also

    do, dolist, dotimes, return, go, throw, Section (Destructuring)


    Except that loop-finish cannot be used within a simple loop form, a simple loop form is related to an extended loop form in the following way:

    (loop {compound-form}*)  (loop do {compound-form}*)