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quasiquote in new reference

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svn: r6995
This commit is contained in:
Matthew Flatt 2007-08-01 21:45:14 +00:00
parent 2c1f5de11e
commit 92f1e3fed2
2 changed files with 67 additions and 1 deletions
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2
collects/scribblings/reference/contracts.scrbl
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@ -123,7 +123,7 @@ Returns a flat contract that requires the input to be a real number
between @scheme[n] and @scheme[m], inclusive.}
@defproc[(integer-in [j exact-integer?][k exact-integer?]) flat-contract?]
@defproc[(integer-in [j exact-integer?][k exact-integer?]) flat-contract?]{
Returns a flat contract that requires the input to be an exact integer
between @scheme[j] and @scheme[k], inclusive.}

66
collects/scribblings/reference/syntax.scrbl
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@ -897,6 +897,72 @@ expression).
@moreref["mz:contmarks"]{continuation marks}}
@;------------------------------------------------------------------------
@section[#:tag "mz:quasiquote"]{Quasiquoting: @scheme[quasiquote], @scheme[unquote], and @scheme[unquote-splicing]}
@defform[(quasiquote datum)]{
The same as @scheme[(quote datum)] if @scheme[datum] does not include
@scheme[(unquote _expr)] or @scheme[(unquote-splicing _expr)]. An
@scheme[(unquote _expr)] expression escapes from the quote, however,
and the result of the @scheme[_expr] takes the place of the
@scheme[(unquote _expr)] form in the @scheme[quasiquote] result. An
@scheme[(unquote-splicing _expr)] similarly escapes, but the
@scheme[_expr] must produce a list, and its elements are spliced as
multiple values place of the @scheme[(unquote-splicing _expr)], which
must appear as the @scheme[car] or a quoted pair.
@examples[
(eval:alts (#,(scheme quasiquote) (0 1 2)) `(0 1 2))
(eval:alts (#,(scheme quasiquote) (0 (#,(scheme unquote) (+ 1 2)) 4)) `(1 ,(+ 1 2) 4))
(eval:alts (#,(scheme quasiquote) (0 (#,(scheme unquote-splicing) (list 1 2)) 4)) `(1 ,@(list 1 2) 4))
]
A @scheme[quasiquote], @scheme[unquote], or @scheme[unquote-splicing]
form is typically abbreviated with @litchar{`}, @litchar{,}, or
@litchar[",@"], respectively. See also @secref["mz:parse-quote"].
@examples[
`(0 1 2)
`(1 ,(+ 1 2) 4)
`(1 ,@(list 1 2) 4)
]
A @scheme[quasiquote] form within the original @scheme[datum]
increments the level of quasiquotation: within the @scheme[quasiquote]
form, each @scheme[unquote] or @scheme[unquote-splicing] is preserved,
but a further nested @scheme[unquote] or @scheme[unquote-splicing]
escapes. Multiple nestings of @scheme[quasiquote] require multiple
nestings of @scheme[unquote] or @scheme[unquote-splicing] to escape.
@examples[
`(1 `,(+ 1 ,(+ 2 3)) 4)
`(1 ```,,@,,@(list (+ 1 2)) 4)
]
The @scheme[quasiquote] form allocates only as many fresh cons cells,
vectors, and boxes as are needed without analyzing @scheme[unquote]
and @scheme[unquote-splicing] expressions. For example, in
@schemeblock[
`(,1 2 3)
]
a single tail @scheme['(2 3)] is used for every evaluation of the
@scheme[quasiquote] expression.
}
@defidform[unquote]{
See @scheme[quasiquote], where @scheme[unquote] is recognized as an
escape. An @scheme[unquote] form as an expression is a syntax error.}
@defidform[unquote-splicing]{
See @scheme[quasiquote], where @scheme[unquote-splicing] is recognized as an
escape. An @scheme[unquote-splicing] form as an expression is a syntax error.}
@;------------------------------------------------------------------------
@section{Syntax Quoting: @scheme[quote-syntax]}