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minor tweaks to define-sequence-syntax docs

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Robby Findler 2015-02-11 09:49:05 -06:00
parent 1409ff1d24
commit 0e563c6ab3
1 changed files with 11 additions and 8 deletions
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19
pkgs/racket-doc/scribblings/reference/for.scrbl
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@ -449,7 +449,7 @@ Like @racket[for*/fold], but the extra @racket[orig-datum] is used as the source
Defines @racket[id] as syntax. An @racket[(id . _rest)] form is
treated specially when used to generate a sequence in a
@racket[_clause] of @racket[for] (or one of its variants). In that
@racket[_for-clause] of @racket[for] (or one of its variants). In that
case, the procedure result of @racket[clause-transform-expr] is called
to transform the clause.
@ -462,18 +462,21 @@ produce a procedure (of one argument) that is used as a macro
transformer.
When the @racket[clause-transform-expr] transformer is used, it is
given a @racket[_clause] as an argument, where the clause's form is
given a @racket[_for-clause] as an argument, where the clause's form is
normalized so that the left-hand side is a parenthesized sequence of
identifiers. The right-hand side is of the form @racket[(id . _rest)].
The result can be either @racket[#f], to indicate that the forms
should not be treated specially (perhaps because the number of bound
identifiers is inconsistent with the @racket[(id . _rest)] form), or a
new @racket[_clause] to replace the given one. The new clause might
new @racket[_for-clause] to replace the given one. The new clause might
use @racket[:do-in]. To protect identifiers in the result of
@racket[clause-transform-expr], use @racket[for-clause-syntax-protect]
instead of @racket[syntax-protect].
@mz-examples[#:eval for-eval
(define (check-nat n)
(unless (exact-nonnegative-integer? n)
(raise-argument-error 'in-digits "exact-nonnegative-integer?" n)))
(define-sequence-syntax in-digits
(lambda () #'in-digits/proc)
(lambda (stx)
@ -482,16 +485,16 @@ instead of @racket[syntax-protect].
#'[(d)
(:do-in
([(n) nat])
(unless (exact-nonnegative-integer? n)
(raise-type-error 'in-digits "exact non-negative integer" n))
(check-nat n)
([i n])
(not (zero? i))
([(j d) (quotient/remainder i 10)])
#true
#true
[j])]])))
[j])]]
[_ #f])))
(define (in-digits/proc n [b 10])
(define (in-digits/proc n)
(for/list ([d (in-digits n)]) d))
(for/list ([d (in-digits 1138)]) d)
@ -509,7 +512,7 @@ instead of @racket[syntax-protect].
(loop-arg ...))]{
A form that can only be used as a @racket[_seq-expr] in a
@racket[_clause] of @racket[for] (or one of its variants).
@racket[_for-clause] of @racket[for] (or one of its variants).
Within a @racket[for], the pieces of the @racket[:do-in] form are
spliced into the iteration essentially as follows: