     Macro LOOP

Syntax:

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)

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 6.1.1.7 (Destructuring).

result---an object.

Description:

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

Examples:

;; An example of the simple form of LOOP.
(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<NEWLINE>
>>  The square root of 5 is 2.236068.
>>  Number: 4<NEWLINE>
>>  The square root of 4 is 2.
>>  Number: done<NEWLINE>
=>  NIL

;; An example of the extended form of LOOP.
(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<NEWLINE>
>>  The square of 4 is 16.
>>  Number: 23<NEWLINE>
>>  The square of 23 is 529.
>>  Number: done<NEWLINE>
=>  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)

Affected By: None.

Exceptional Situations: None.      