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docs: correct description of custom-port special results

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There no longer seems to be any path that uses the 0-arity option for
a read result from a custom input-port that is a function for a
"special" result. Probably, that path got lost when I added a `source`
optional argument to `read-char-or-special`. If so, that effect of the
change wasn't intentional, but let's just be happy that a
simplification is in place.
This commit is contained in:
Matthew Flatt 2018-10-10 17:45:04 -06:00
parent 16347b434d
commit 694fe2e55c
1 changed files with 5 additions and 22 deletions
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27
pkgs/racket-doc/scribblings/reference/custom-ports.scrbl
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@ -71,8 +71,8 @@ The arguments implement the port as follows:
@item{@racket[eof];}
@item{a procedure of arity four (representing a ``special''
result, as discussed @elemref["special"]{further below}) and
optionally of arity zero, but a procedure result is allowed only
result, as discussed @elemref["special"]{further below}),
but a procedure result is allowed only
when @racket[peek] is not @racket[#f];}
@item{a @techlink{pipe} input port that supplies bytes to be
@ -377,26 +377,9 @@ The arguments implement the port as follows:
return a character or @racket[eof]; in particular, @racket[read-char]
raises an exception if it encounters a special-result procedure, even
if the procedure produces a byte.) A special-result procedure must
accept four arguments, and it can optionally accept zero arguments:
@itemize[
@item{When the special read is triggered by @racket[read-syntax],
@racket[read-syntax/recursive] the
procedure is passed four arguments that represent a source
location. Four arguments for a source location are also provided when
the read is triggered by @racket[read-byte-or-special],
@racket[read-char-or-special], @racket[peek-byte-or-special], or
@racket[peek-char-or-special] with a non-@racket[#f] source name.}
@item{When the special read is triggered by @racket[read],
@racket[read/recursive], or other calls to
@racket[read-byte-or-special], @racket[read-char-or-special],
@racket[peek-byte-or-special], or @racket[peek-char-or-special], the
procedure is passed no arguments if it accepts zero arguments,
otherwise it is passed four arguments that are all @racket[#f].}
]
accept four arguments that represent a source location. The first
argument is @racket[#f] when the special read is triggered by @racket[read]
or @racket[read/recursive].
The special-value procedure can return an arbitrary value, and it
will be called zero or one times (not necessarily before further