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}*]
[end]
|
| 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)
|
| 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 Destructuring. |
| result | an object. |
For details, see 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.~
⇒ SQRT-ADVISOR
(sqrt-advisor)
|> Number: |>>5[<–~]<<|
|> The square root of 5 is 2.236068.
|> Number: |>>4[<–~]<<|
|> The square root of 4 is 2.
|> Number: |>>done[<–~]<<|
⇒ NIL
;; 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.~
⇒ SQUARE-ADVISOR
(square-advisor)
|> Number: |>>4[<–~]<<|
|> The square of 4 is 16.
|> Number: |>>23[<–~]<<|
|> The square of 23 is 529.
|> Number: |>>done[<–~]<<|
⇒ NIL
;; 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)
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}*)