(define+provide+safe(attr-reftxkey[failure-result(λ_(raise(make-exn:fail:contract(format"attr-ref: no value found for key ~v"key)(current-continuation-marks))))])
@ -50,35 +50,33 @@ It's an X-expression with the following grammar:
[element xexpr?]
[element xexpr?]
]
]
A txexpr is a list with a symbol in the first position— the @italic{tag} — followed by a series of @italic{elements}, which are other X-expressions. Optionally, a txexpr can have a list of @italic{attributes} in the second position.
A tagged X-expression — @italic{txexpr} for short — is a list with a symbol in the first position— the @italic{tag} — followed by a series of @italic{elements}, which are other X-expressions. Optionally, a txexpr can have a list of @italic{attributes} in the second position.
The last one is a common mistake. Because the key–value pair is not enclosed in a @racket[list], it's interpreted as a nested txexpr within the first txexpr, as you may not find out until you try to read its attributes:
The last one is a common mistake. Because the key–value pair is not enclosed in a @tech[#:doc '(lib "scribblings/guide/guide.scrbl")]{list}, it's interpreted as a nested txexpr within the first txexpr, as you may not find out until you try to read its attributes:
@margin-note{There's no way of eliminating this ambiguity, short of always requiring an attribute list — empty if necessary —in your txexpr. See also @racket[xexpr-drop-empty-attributes].}
After converting to and from HTML, we get back the original X-expression. Well, almost. The brackets turned into parentheses — no big deal, since they mean the same thing in Racket. Also, per its usual practice, @racket[string->xexpr] added an empty attribute list after @racket[em]. This is also benign.
After converting to and from HTML, we get back the original X-expression. Well, almost. Per its usual practice, @racket[string->xexpr] added an empty attribute list after @racket[em]. This is benign —an empty attribute list can be omitted with no change in meaning, or vice versa.
@section{Why not just use @exec{match}, @exec{quasiquote}, and so on?}
@section{Why not just use @exec{match}, @exec{quasiquote}, and so on?}
@ -90,7 +88,8 @@ If you prefer those, please do. But I've found two benefits to using module func
The programming is trivial, but the annoyance is real.
The programming is trivial, but the annoyance is real.
@section{Interface}
@section{Predicates}
@deftogether[(
@deftogether[(
@defproc[
@defproc[
@ -154,24 +153,7 @@ boolean?]
[v any/c])
[v any/c])
boolean?]
boolean?]
)]
)]
Shorthand for @code{(listof txexpr-tag?)}, @code{(listof txexpr-attr?)}, and @code{(listof txexpr-element?)}.
Predicates equivalent to a list of @code{txexpr-tag?}, @code{txexpr-attr?}, or @code{txexpr-element?}, respectively.
@defproc[
(validate-txexpr
[possible-txexpr any/c])
txexpr?]
Like @racket[txexpr?], but raises a descriptive error if @racket[_possible-txexpr] is invalid, and otherwise returns @racket[_possible-txexpr] itself.
Predicates for input arguments that are trivially converted to an attribute @racket[_key] or @racket[_value]…
Predicates for input arguments that can be trivially converted to an attribute @racket[_key] or @racket[_value] with the associated conversion functions.
@examples[#:eval my-eval
(can-be-txexpr-attr-key? 'symbol)
(can-be-txexpr-attr-key? "string-val")
(can-be-txexpr-attr-key? (list 1 2 3))
(can-be-txexpr-attr-value? 'symbol)
(can-be-txexpr-attr-value? "string-val")
(can-be-txexpr-attr-value? (list 1 2 3))
]
@deftogether[(
@defproc[
(->txexpr-attr-key
[v can-be-txexpr-attr-key?])
txexpr-attr-key?]
@defproc[
@defproc[
(->txexpr-attr-value
(can-be-txexpr-attrs?
[v can-be-txexpr-attr-value?])
[v any/c])
txexpr-attr-value?]
boolean?]
)]
Predicate for functions that handle @racket[_txexpr-attrs]. Covers values that are easily converted into pairs of @racket[_attr-key] and @racket[_attr-value]. Namely: single @racket[_xexpr-attr]s, lists of @racket[_xexpr-attr]s (i.e., what you get from @racket[get-attrs]), or interleaved symbols and strings (each pair will be concatenated into a single @racket[_xexpr-attr]).
Convert @racket[_x] to an HTML string. Better than @racket[xexpr->string] because consistent with the HTML spec, it will not escape text that appears within @code{script} or @code{style} blocks. For convenience, this function will take any X-expression, not just tagged X-expressions.
[elements txexpr-elements? @empty])
txexpr?]
Assemble a @racket[_txexpr] from its parts. If you don't have attributes, but you do have elements, you'll need to pass @racket[empty] (or @racket[null] or @racket['()]) as the second argument. Note that unlike @racket[xml->xexpr], if the attribute list is empty, it's not included in the resulting expression.
Assemble a @racket[_txexpr] from its parts. If you don't have attributes, but you do have elements, you'll need to pass @racket[empty] as the second argument. Note that unlike @racket[xml->xexpr], if the attribute list is empty, it's not included in the resulting expression.
Predicate for functions that handle @racket[_txexpr-attrs]. Covers values that are easily converted into pairs of @racket[_attr-key] and @racket[_attr-value]. Namely: single @racket[_xexpr-attr]s, lists of @racket[_xexpr-attr]s (i.e., what you get from @racket[get-attrs]), or interleaved symbols and strings (each pair will be concatenated into a single @racket[_xexpr-attr]).
txexpr-attrs?
txexpr-elements?)]
)]
Dissolve a @racket[_txexpr] into its components. @racket[txexpr->values] returns the components as multiple values; @racket[txexpr->list] returns them in a list.
Convert @racket[_attrs] to an immutable hash, and back again.
Convert @racket[_attrs] to an immutable hash, and back again. Following the convention specified for @link["https://www.w3.org/TR/xml/#attdecls"]{XML parsers}, the @italic{first} appearance of an attribute name binds the value —later attributes with the same name are ignored. If you prefer the typical @racket[hash] behavior where later values override earlier ones, set @racket[#:hash-style?] to @racket[#t].
@ -340,42 +322,36 @@ Returns @racket[#t] if the @racket[_attrs] contain a value for the given @racket
[attrs (or/c txexpr-attrs? txexpr?)]
[attrs (or/c txexpr-attrs? txexpr?)]
[other-attrs (or/c txexpr-attrs? txexpr?)])
[other-attrs (or/c txexpr-attrs? txexpr?)])
boolean?]
boolean?]
Returns @racket[#t] if @racket[_attrs] and @racket[_other-attrs] contain the same keys and values, @racket[#f] otherwise. The order of attributes is irrelevant.
Return @racket[#t] if @racket[_attrs] and @racket[_other-attrs] contain the same keys and values, @racket[#f] otherwise. The order of attributes is irrelevant. (If order matters to you, use good old @racket[equal?] instead.)
Given a @racket[_key], look up the corresponding @racket[_value] in the attributes of a @racket[_txexpr]. Asking for a nonexistent key produces an error.
])
any]
Given a @racket[_key], return the corresponding @racket[_value] from the attributes of a @racket[_txexpr]. By default, asking for a nonexistent key produces an error. But if a value or procedure is provided as the @racket[_failure-result], evaluate and return that instead.
@examples[#:eval my-eval
@examples[#:eval my-eval
(attr-ref tx 'class)
(attr-ref tx 'class)
(attr-ref tx 'id)
(attr-ref tx 'id)
(attr-ref tx 'nonexistent-key)
(attr-ref tx 'nonexistent-key)
(attr-ref tx 'nonexistent-key "forty-two")
(attr-ref tx 'nonexistent-key (λ _ (* 6 7)))
]
]
@defproc[
@deftogether[(
(attr-ref*
[tx txexpr?]
[key can-be-txexpr-attr-key?])
(listof can-be-txexpr-attr-value?)]
Like @racket[attr-ref], but returns a recursively gathered list of all the @racket[_value]s for that key within @racket[_tx]. Asking for a nonexistent key produces @racket[null].
@examples[#:eval my-eval
(define tx '(div [[class "red"]] "Hello" (em ([class "blue"]) "world")))
(attr-ref* tx 'class)
(attr-ref* tx 'nonexistent-key)
]
@defproc[
@defproc[
(attr-set
(attr-set
@ -383,14 +359,7 @@ Like @racket[attr-ref], but returns a recursively gathered list of all the @rack
[key can-be-txexpr-attr-key?]
[key can-be-txexpr-attr-key?]
[value can-be-txexpr-attr-value?])
[value can-be-txexpr-attr-value?])
txexpr?]
txexpr?]
Given a @racket[_txexpr], set the value of attribute @racket[_key] to @racket[_value]. Return the updated @racket[_txexpr].
@ -398,67 +367,54 @@ Given a @racket[_txexpr], set the value of attribute @racket[_key] to @racket[_v
[key can-be-txexpr-attr-key?]
[key can-be-txexpr-attr-key?]
[value can-be-txexpr-attr-value?] ... ... )
[value can-be-txexpr-attr-value?] ... ... )
txexpr?]
txexpr?]
Like @racket[attr-set], but accepts any number of keys and values.
)]
Set the value of attribute @racket[_key] to @racket[_value] in @racket[_txexpr]. Return the updated @racket[_txexpr]. Duplicate attributes, if they exist, are resolved using @racket[attr->hash]. @racket[attr-set] only accepts one key and one value; @racket[attr-set*] accepts any number.
Given a @racket[_txexpr], append the value of attribute @racket[_key] with @racket[_value]. Return the updated @racket[_txexpr].
Given a @racket[_txexpr], append attribute @racket[_key] with @racket[_value]. Return the updated @racket[_txexpr]. If @racket[_key] doesn't already exist, then add a new attribute (i.e., behave like @racket[attr-set]).
@examples[#:eval my-eval
@examples[#:eval my-eval
(define tx '(div [[class "red"]] "Hello"))
(define tx '(div ((class "red")) "Hello"))
(attr-join tx 'class "small")
(attr-join tx 'class "small")
(attr-join tx 'klass "small")
]
]
@defproc[
(merge-attrs
[attrs (listof can-be-txexpr-attrs?)] ...)
txexpr-attrs?]
Combine a series of attributes into a single @racket[_txexpr-attrs] item. This function addresses three annoyances that surface in working with txexpr attributes.
@itemlist[#:style 'ordered
@item{You can pass the attributes in multiple forms. See @racket[can-be-txexpr-attrs?] for further details.}
@item{Attributes with the same name are merged, with the later value taking precedence (i.e., @racket[hash] behavior). }
@item{Attributes are sorted in alphabetical order.}]
Recursively apply @racket[_proc] to all elements, leaving tags and attributes alone. Using plain @racket[map] will only process elements at the top level of the current @racket[_txexpr]. Usually that's not what you want.
Recursively apply @racket[_proc] to all elements, leaving tags and attributes alone. Using plain @racket[map] will only process elements at the top level of @racket[_tx]. Usually that's not what you want.
@ -467,7 +423,7 @@ Recursively apply @racket[_proc] to all elements, leaving tags and attributes al
(map-elements upcaser tx)
(map-elements upcaser tx)
]
]
In practice, most @racket[_xexpr-element]s are strings. But woe befalls those who pass string procedures to @racket[map-elements], because an @racket[_xexpr-element] can be any kind of @racket[xexpr?], and an @racket[xexpr?] is not necessarily a string.
In practice, most @racket[_txexpr-element]s are strings. But it's unwise to pass string-only procedures to @racket[map-elements], because an @racket[_txexpr-element] can be any kind of @racket[xexpr?], and an @racket[xexpr?] is not necessarily a string.
@ -476,30 +432,6 @@ In practice, most @racket[_xexpr-element]s are strings. But woe befalls those wh
(map-elements upcaser tx)
(map-elements upcaser tx)
]
]
@defproc[
(map-elements/exclude
[proc procedure?]
[tx txexpr?]
[exclude-test (txexpr? . -> . boolean?)])
txexpr?]
Like @racket[map-elements], but skips any @racket[_txexprs] that evaluate to @racket[#t] under @racket[_exclude-test]. The @racket[_exclude-test] gets a whole txexpr as input, so it can test any of its parts.
Be careful with the wider consequences of exclusion tests. When @racket[_exclude-test] is true, the @racket[_txexpr] is excluded, but so is everything underneath that @racket[_txexpr]. In other words, there is no way to re-include (un-exclude?) elements nested under an excluded element.
@ -526,17 +458,19 @@ Ordinarily, the result of the split operation is to remove the elements that mat
@deftogether[(
@deftogether[(
@defproc[
@defproc[
(findf*-txexpr
(findf-txexpr
[tx txexpr?]
[tx txexpr?]
[pred procedure?])
[pred procedure?])
(or/c #f (listof txexpr-element?))]
(or/c #f txexpr-element?)]
@defproc[
@defproc[
(findf-txexpr
(findf*-txexpr
[tx txexpr?]
[tx txexpr?]
[pred procedure?])
[pred procedure?])
(or/c #f txexpr-element?)]
(or/c #f (listof txexpr-element?))]
)]
)]
Like @racket[splitf-txexpr], but only retrieve the elements that match @racket[_pred]. @racket[findf*-txexpr] retrieves all results; @racket[findf-txexpr] only the first. In both cases, if there are no matches, you get @racket[#f].
Like @racket[splitf-txexpr], but only retrieve the elements that match @racket[_pred]. @racket[findf*-txexpr] retrieves all results; @racket[findf-txexpr] only the first. In both cases, if there are no matches, you get @racket[#f].
@ -552,6 +486,25 @@ Like @racket[splitf-txexpr], but only retrieve the elements that match @racket[_
]
]
@section{HTML conversion}
@defproc[
(xexpr->html
[x xexpr?])
string?]
Convert @racket[_x] to an HTML string. Better than @racket[xexpr->string] because consistent with the HTML spec, it will skip the content of @code{script} or @code{style} blocks. For convenience, this function will take any X-expression, not just tagged X-expressions.
