@ -75,9 +75,9 @@ When I use ``datum'' in its specific Racket sense, I use ``datums'' as its plura
@defproc[
@defproc[
(format-datum
(format-datum
[datum-form datum?]
[datum-form (or/c list? symbol?)]
[val any/c?] ...)
[val any/c?] ...)
datum?]{
(or/c list? symbol?)]{
Similar to @racket[format], but the template @racket[datum-form] is a datum, rather than a string, and the function returns a datum, rather than a string. Otherwise, the same formatting escapes can be used in the template (see @racket[fprintf]).
Similar to @racket[format], but the template @racket[datum-form] is a datum, rather than a string, and the function returns a datum, rather than a string. Otherwise, the same formatting escapes can be used in the template (see @racket[fprintf]).
Two special cases. First, a string that describes a list of datums is parenthesized so the result is a single datum. Second, an empty string returns @racket[void] (not @racket[#f], because that's a legitimate datum).
Two special cases. First, a string that describes a list of datums is parenthesized so the result is a single datum. Second, an empty string returns @racket[void] (not @racket[#f], because that's a legitimate datum).
@ -94,9 +94,9 @@ Two special cases. First, a string that describes a list of datums is parenthesi
@defproc[
@defproc[
(format-datums
(format-datums
[datum-form datum?]
[datum-form (or/c list? symbol?)]
[vals (listof any/c?)] ...)
[vals (listof any/c?)] ...)
(listof datum?)]{
(listof (or/c list? symbol?))]{
Like @racket[format-datum], but applies @racket[datum-form] to the lists of @racket[vals] in similar way to @racket[map], where values for the format string are taken from the lists of @racket[vals] in parallel. This means that a) @racket[datum-form] must accept as many arguments as there are lists of @racket[vals], and b) the lists of @racket[vals] must all have the same number of items.
Like @racket[format-datum], but applies @racket[datum-form] to the lists of @racket[vals] in similar way to @racket[map], where values for the format string are taken from the lists of @racket[vals] in parallel. This means that a) @racket[datum-form] must accept as many arguments as there are lists of @racket[vals], and b) the lists of @racket[vals] must all have the same number of items.
@examples[#:eval my-eval
@examples[#:eval my-eval
@ -108,6 +108,7 @@ Like @racket[format-datum], but applies @racket[datum-form] to the lists of @rac
]
]
}
}
@section{Debugging}
@section{Debugging}
@defmodule[br/debug]
@defmodule[br/debug]
@ -211,7 +212,7 @@ Create a macro using one of the subforms above, which are explained below:
If the first argument is an identifier @racket[id] and the second a syntaxed identifier that looks like @racket[(syntax other-id)], create a @tech{rename transformer}, which is a fancy term for ``macro that replaces @racket[id] with @racket[other-id].'' (This subform is equivalent to @racket[make-rename-transformer].)
If the first argument is an identifier @racket[id] and the second a syntaxed identifier that looks like @racket[(syntax other-id)], create a rename transformer, which is a fancy term for ``macro that replaces @racket[id] with @racket[other-id].'' (This subform is equivalent to @racket[make-rename-transformer].)
Why do we need rename transformers? Because an ordinary macro operates on its whole calling expression (which it receives as input) like @racket[(macro-name this-arg that-arg . and-so-on)]. By contrast, a rename transformer operates only on the identifier itself (regardless of where that identifier appears in the code). It's like making one identifier into an alias for another identifier.
Why do we need rename transformers? Because an ordinary macro operates on its whole calling expression (which it receives as input) like @racket[(macro-name this-arg that-arg . and-so-on)]. By contrast, a rename transformer operates only on the identifier itself (regardless of where that identifier appears in the code). It's like making one identifier into an alias for another identifier.
@ -259,7 +260,7 @@ nice-summer
@specsubform[#:literals (define-macro)
@specsubform[#:literals (define-macro)
(define-macro id syntax-object)
(define-macro id syntax-object)
#:contracts ([syntax-object syntax?])]{
#:contracts ([syntax-object syntax?])]{
If the first argument is an @racket[id] and the second a @racket[syntax-object], create a syntax transformer that returns @racket[syntax-object]. This is just alternate notation for the previous subform, wrapping @racket[syntax-object] inside a function body. The effect is to create a macro from @racket[id] that always returns @racket[syntax-object], regardless of how it's invoked. Not especially useful within programs. Mostly handy for making quick macros at the @tech{REPL}.
If the first argument is an @racket[id] and the second a @racket[syntax-object], create a syntax transformer that returns @racket[syntax-object]. This is just alternate notation for the previous subform, wrapping @racket[syntax-object] inside a function body. The effect is to create a macro from @racket[id] that always returns @racket[syntax-object], regardless of how it's invoked. Not especially useful within programs. Mostly handy for making quick macros at the REPL.
@examples[#:eval my-eval
@examples[#:eval my-eval
(define-macro bad-listener #'"what?")
(define-macro bad-listener #'"what?")
@ -320,7 +321,7 @@ The error is cleared when the argument is capitalized, thus making it a wilcard:
(good-squarer +10i)
(good-squarer +10i)
]
]
You can use the special identifier @racket[caller-stx] —available only within the body of @racket[define-macro] —to access the original input argument to the macro.
@;{You can use the special identifier @racket[caller-stx] —available only within the body of @racket[define-macro] —to access the original input argument to the macro.}
@;{todo: fix this example. complains that caller-stx is unbound}
@;{todo: fix this example. complains that caller-stx is unbound}
