convert input to txexpr-attr-value (closes #17)

* add documentation for txexpr as a match pattern
* docs: require racket/match for examples

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  run:
+    name: "Build using Racket '${{ matrix.racket-version }}' (${{ matrix.racket-variant }})"
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        racket-version: ["6.6", "6.7", "6.8", "6.9", "6.10.1", "6.11", "6.12", "7.0", "7.1", "7.2", "7.3", "7.4", "7.5", "7.6", "7.7", "7.8", "7.9", "current"]
+        racket-variant: ["BC", "CS"]
+        # CS builds are only provided for versions 7.4 and up so avoid
+        # running the job for prior versions.
+        exclude:
+          - {racket-version: "6.6",    racket-variant: "CS"}
+          - {racket-version: "6.7",    racket-variant: "CS"}
+          - {racket-version: "6.8",    racket-variant: "CS"}
+          - {racket-version: "6.9",    racket-variant: "CS"}
+          - {racket-version: "6.10.1", racket-variant: "CS"}
+          - {racket-version: "6.11",   racket-variant: "CS"}
+          - {racket-version: "6.12",   racket-variant: "CS"}
+          - {racket-version: "7.0",    racket-variant: "CS"}
+          - {racket-version: "7.1",    racket-variant: "CS"}
+          - {racket-version: "7.2",    racket-variant: "CS"}
+          - {racket-version: "7.3",    racket-variant: "CS"}
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@master
+
+    - uses: Bogdanp/setup-racket@v0.11
+      with:
+        distribution: 'full'
+        version: ${{ matrix.racket-version }}
+        variant: ${{ matrix.racket-variant }}
+
+    - name: Install Txexpr and its dependencies
+      run: raco pkg install --auto --batch
+
+    - name: Run the tests
+      run: xvfb-run raco test -j 4 -p txexpr

.travis.yml

@@ -1,45 +0,0 @@
-# adapted from
-# https://github.com/greghendershott/travis-racket/blob/master/.travis.yml
-# Thanks Greg!
-
-language: c
-sudo: false
-
-env:
-  global:
-    - RACKET_DIR=~/racket
-  matrix:
-    - RACKET_VERSION=6.0
-    - RACKET_VERSION=6.1
-    - RACKET_VERSION=6.2
-    - RACKET_VERSION=6.3
-    - RACKET_VERSION=6.4
-    - RACKET_VERSION=6.5
-    - RACKET_VERSION=6.6
-    - RACKET_VERSION=6.7
-    - RACKET_VERSION=6.8
-    - RACKET_VERSION=6.9
-    - RACKET_VERSION=6.10
-    - RACKET_VERSION=6.11
-    - RACKET_VERSION=6.12
-    - RACKET_VERSION=HEAD
-
-# You may want to test against certain versions of Racket, without
-# having them count against the overall success/failure.
-matrix:
-  allow_failures:
-  #  - env: RACKET_VERSION=HEAD
-  # Fast finish: Overall build result is determined as soon as any of
-  # its rows have failed, or, all of its rows that aren't allowed to
-  # fail have succeeded.
-  fast_finish: true
-
-before_install:
-  - git clone https://github.com/mbutterick/travis-racket.git
-  - cat travis-racket/install-racket.sh | bash # pipe to bash not sh!
-  - export PATH="${RACKET_DIR}/bin:${PATH}" #install-racket.sh can't set for us
-
-script:
- - cd ..   # Travis did a cd into the dir. Back up, for the next:
- - raco pkg install --deps search-auto --link txexpr
- - raco test -p txexpr

LGPL.txt

@@ -1,165 +0,0 @@
-GNU LESSER GENERAL PUBLIC LICENSE
-                       Version 3, 29 June 2007
-
- Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
- Everyone is permitted to copy and distribute verbatim copies
- of this license document, but changing it is not allowed.
-
-
-  This version of the GNU Lesser General Public License incorporates
-the terms and conditions of version 3 of the GNU General Public
-License, supplemented by the additional permissions listed below.
-
-  0. Additional Definitions.
-
-  As used herein, "this License" refers to version 3 of the GNU Lesser
-General Public License, and the "GNU GPL" refers to version 3 of the GNU
-General Public License.
-
-  "The Library" refers to a covered work governed by this License,
-other than an Application or a Combined Work as defined below.
-
-  An "Application" is any work that makes use of an interface provided
-by the Library, but which is not otherwise based on the Library.
-Defining a subclass of a class defined by the Library is deemed a mode
-of using an interface provided by the Library.
-
-  A "Combined Work" is a work produced by combining or linking an
-Application with the Library.  The particular version of the Library
-with which the Combined Work was made is also called the "Linked
-Version".
-
-  The "Minimal Corresponding Source" for a Combined Work means the
-Corresponding Source for the Combined Work, excluding any source code
-for portions of the Combined Work that, considered in isolation, are
-based on the Application, and not on the Linked Version.
-
-  The "Corresponding Application Code" for a Combined Work means the
-object code and/or source code for the Application, including any data
-and utility programs needed for reproducing the Combined Work from the
-Application, but excluding the System Libraries of the Combined Work.
-
-  1. Exception to Section 3 of the GNU GPL.
-
-  You may convey a covered work under sections 3 and 4 of this License
-without being bound by section 3 of the GNU GPL.
-
-  2. Conveying Modified Versions.
-
-  If you modify a copy of the Library, and, in your modifications, a
-facility refers to a function or data to be supplied by an Application
-that uses the facility (other than as an argument passed when the
-facility is invoked), then you may convey a copy of the modified
-version:
-
-   a) under this License, provided that you make a good faith effort to
-   ensure that, in the event an Application does not supply the
-   function or data, the facility still operates, and performs
-   whatever part of its purpose remains meaningful, or
-
-   b) under the GNU GPL, with none of the additional permissions of
-   this License applicable to that copy.
-
-  3. Object Code Incorporating Material from Library Header Files.
-
-  The object code form of an Application may incorporate material from
-a header file that is part of the Library.  You may convey such object
-code under terms of your choice, provided that, if the incorporated
-material is not limited to numerical parameters, data structure
-layouts and accessors, or small macros, inline functions and templates
-(ten or fewer lines in length), you do both of the following:
-
-   a) Give prominent notice with each copy of the object code that the
-   Library is used in it and that the Library and its use are
-   covered by this License.
-
-   b) Accompany the object code with a copy of the GNU GPL and this license
-   document.
-
-  4. Combined Works.
-
-  You may convey a Combined Work under terms of your choice that,
-taken together, effectively do not restrict modification of the
-portions of the Library contained in the Combined Work and reverse
-engineering for debugging such modifications, if you also do each of
-the following:
-
-   a) Give prominent notice with each copy of the Combined Work that
-   the Library is used in it and that the Library and its use are
-   covered by this License.
-
-   b) Accompany the Combined Work with a copy of the GNU GPL and this license
-   document.
-
-   c) For a Combined Work that displays copyright notices during
-   execution, include the copyright notice for the Library among
-   these notices, as well as a reference directing the user to the
-   copies of the GNU GPL and this license document.
-
-   d) Do one of the following:
-
-       0) Convey the Minimal Corresponding Source under the terms of this
-       License, and the Corresponding Application Code in a form
-       suitable for, and under terms that permit, the user to
-       recombine or relink the Application with a modified version of
-       the Linked Version to produce a modified Combined Work, in the
-       manner specified by section 6 of the GNU GPL for conveying
-       Corresponding Source.
-
-       1) Use a suitable shared library mechanism for linking with the
-       Library.  A suitable mechanism is one that (a) uses at run time
-       a copy of the Library already present on the user's computer
-       system, and (b) will operate properly with a modified version
-       of the Library that is interface-compatible with the Linked
-       Version.
-
-   e) Provide Installation Information, but only if you would otherwise
-   be required to provide such information under section 6 of the
-   GNU GPL, and only to the extent that such information is
-   necessary to install and execute a modified version of the
-   Combined Work produced by recombining or relinking the
-   Application with a modified version of the Linked Version. (If
-   you use option 4d0, the Installation Information must accompany
-   the Minimal Corresponding Source and Corresponding Application
-   Code. If you use option 4d1, you must provide the Installation
-   Information in the manner specified by section 6 of the GNU GPL
-   for conveying Corresponding Source.)
-
-  5. Combined Libraries.
-
-  You may place library facilities that are a work based on the
-Library side by side in a single library together with other library
-facilities that are not Applications and are not covered by this
-License, and convey such a combined library under terms of your
-choice, if you do both of the following:
-
-   a) Accompany the combined library with a copy of the same work based
-   on the Library, uncombined with any other library facilities,
-   conveyed under the terms of this License.
-
-   b) Give prominent notice with the combined library that part of it
-   is a work based on the Library, and explaining where to find the
-   accompanying uncombined form of the same work.
-
-  6. Revised Versions of the GNU Lesser General Public License.
-
-  The Free Software Foundation may publish revised and/or new versions
-of the GNU Lesser General Public License from time to time. Such new
-versions will be similar in spirit to the present version, but may
-differ in detail to address new problems or concerns.
-
-  Each version is given a distinguishing version number. If the
-Library as you received it specifies that a certain numbered version
-of the GNU Lesser General Public License "or any later version"
-applies to it, you have the option of following the terms and
-conditions either of that published version or of any later version
-published by the Free Software Foundation. If the Library as you
-received it does not specify a version number of the GNU Lesser
-General Public License, you may choose any version of the GNU Lesser
-General Public License ever published by the Free Software Foundation.
-
-  If the Library as you received it specifies that a proxy can decide
-whether future versions of the GNU Lesser General Public License shall
-apply, that proxy's public statement of acceptance of any version is
-permanent authorization for you to choose that version for the
-Library.

LICENSE

@@ -1,3 +0,0 @@
-Txexpr
-© 2014-2016 Matthew Butterick
-Licensed under the LGPL (see "LGPL.txt")

LICENSE.md

@@ -0,0 +1,9 @@
+MIT License for txexpr
+
+© 2014-2019 Matthew Butterick
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -1,5 +1,5 @@
-txexpr [![Build Status](https://travis-ci.org/mbutterick/txexpr.svg)](https://travis-ci.org/mbutterick/txexpr)
+## txexpr ![Build Status](https://github.com/mbutterick/txexpr/workflows/CI/badge.svg)
----------------
+
 
 Convenience functions for working with HTML-style tagged X-expressions in Racket 6.0+.
 
@@ -15,4 +15,13 @@ In safe mode (with contracts):
 
     (require (submod txexpr safe))
 
-Full docs are installed with the package. You can also [read the docs here](http://pkg-build.racket-lang.org/doc/txexpr).
+Full docs are installed with the package. You can also [read the docs here](http://pkg-build.racket-lang.org/doc/txexpr).
+
+## License
+
+MIT
+
+
+## Project status
+
+Complete. I will maintain the code but no major updates are planned. Certain aspects of the API and implementation could be better, because much of this code was originally written during a more naive era of personal Racketeering. Still, it gets the job done, and I personally lack enthusiasm for diving back in.

txexpr/base.rkt

@@ -1,6 +1,10 @@
 #lang racket/base
-(require racket/match sugar/define sugar/list sugar/coerce racket/string racket/list xml)
+(require racket/match sugar/define sugar/list sugar/coerce
-(provide cdata? cdata valid-char? xexpr->string xexpr?) ; from xml
+         racket/string racket/list
+         xml
+         "private/define-provide-safe-match.rkt"
+         (for-syntax racket/base syntax/parse))
+(provide cdata? cdata valid-char? xexpr->string xexpr? comment comment?) ; from xml
 (provide empty) ; from racket/list
 
 ;; Section 2.2 of XML 1.1
@@ -81,34 +85,42 @@
       (txexpr-attr? x)
       (txexpr-attrs? x)))
 
-(define (validate-txexpr-attrs x #:context [txexpr-context #f])
+(define (validate-txexpr-attrs tx)
-  (match x
+  (andmap
-    [(list (? txexpr-attr? x) ...) x]
+   (lambda (attr)
-    [_ (raise-argument-error 'validate-txexpr-attrs
+     (unless (and (list? attr) (eq? 2 (length attr)))
-                             (string-append 
+       (txexpr-error "attribute" "is not a list of the form '(symbol \"string\")" attr tx))
-                              (if txexpr-context (format "in ~v, " txexpr-context) "")
+     (unless (symbol? (first attr))
-                              (format "list of attributes, each in the form '(symbol \"string\")")) x)]))
+       (txexpr-error "attribute key" "is not a symbol" (first attr) tx))
-
+     (unless (string? (second attr))
-
+       (txexpr-error "attribute value" "is not a string" (second attr) tx))
-(define (validate-txexpr-element x #:context [txexpr-context #f])
+     #t)
-  (unless (or (string? x) (symbol? x) (valid-char? x) (cdata? x) (txexpr? x))
+   (second tx)))
-    (raise-argument-error
+
-     'validate-txexpr-element
+(define (validate-txexpr-elements elems tx)
-     (string-append
+  (andmap
-      (if txexpr-context (format "in ~v, " txexpr-context) "")
+   (lambda (e)
-      "valid element (= txexpr, string, symbol, XML char, or cdata)") x))
+     (cond
-  x)
+       [(or (string? e) (symbol? e) (my-valid-char? e) (cdata? e) (comment? e)) #t]
+       [(and (list? e) (symbol? (first e)))
+        (validate-txexpr e)]
+       [else (txexpr-error "element" "not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)" e tx)]))
+   elems))
+  
+(define (txexpr-error noun has-problem bad tx)
+  (raise-arguments-error 'validate-txexpr (format "~a ~a" noun has-problem) noun bad "in" tx))
 
 ;; is it a named x-expression?
-;; todo: rewrite this recursively so errors can be pinpointed (for debugging)
+;; Restricting to primitive predicates allows for more specific (helpful) errors
 (define+provide+safe (validate-txexpr x)
   (any/c . -> . txexpr?)
+  (unless (list? x) (raise-argument-error 'validate-txexpr "tagged X-expression" x))
   (match x
-    [(cons (? txexpr-tag?) _)
+    [(list* tag _) #:when (not (symbol? tag))
-     (and
+                   (txexpr-error "tag" "must be a symbol" tag x)]
-      (validate-txexpr-attrs (get-attrs x) #:context x)
+    [(list* tag (or (? null?) (list (? list?) _ ...)) elems)
-      (andmap (λ (e) (validate-txexpr-element e #:context x)) (get-elements x)) x)]
+     (and (validate-txexpr-attrs x) (validate-txexpr-elements elems x) x)]
-    [_ (raise-argument-error 'validate-txexpr "valid X-expression" x)]))
+    [(list* tag elems) (and (validate-txexpr-elements elems x) x)]))
 
 (define (txexpr-unsafe tag attrs elements)
   (cons tag (match attrs
@@ -124,9 +136,15 @@
     (raise-argument-error func-name "txexpr-elements?" elements))
   (txexpr-unsafe tag attrs elements))
 
-(define+provide+safe (txexpr tag [attrs null] [elements null])
+(define+provide+safe+match (txexpr tag [attrs null] [elements null])
   ((txexpr-tag?) (txexpr-attrs? txexpr-elements?) . ->* . txexpr?)
-  (txexpr-base 'txexpr tag attrs elements))
+  (txexpr-base 'txexpr tag attrs elements)
+  #:match-expander
+  (syntax-parser
+    [(_ tag-pat:expr
+        {~optional attrs-pat:expr #:defaults ([attrs-pat #'_])}
+        {~optional elements-pat:expr #:defaults ([elements-pat #'_])})
+     #'(? txexpr? (app txexpr->values tag-pat attrs-pat elements-pat))]))
 
 (define+provide+safe (txexpr* tag [attrs null] . elements)
   ((txexpr-tag?) (txexpr-attrs?) #:rest txexpr-elements? . ->* . txexpr?)
@@ -222,12 +240,14 @@
 (define+provide+safe (attr-join tx key value)
   (txexpr? can-be-txexpr-attr-key? can-be-txexpr-attr-value? . -> . txexpr?)
   (define starting-values (string-split (attr-ref tx key "")))
-  (attr-set tx key (string-join (append starting-values (list value)) " ")))      
+  (attr-set tx key (string-join (append starting-values (list (->txexpr-attr-value value))) " ")))      
 
 (define no-failure-result (gensym)) ; failure-result might be #false
-(define+provide+safe (attr-ref tx key [failure-result no-failure-result])
+(define+provide+safe (attr-ref attrs-arg key [failure-result no-failure-result])
-  ((txexpr? can-be-txexpr-attr-key?) (any/c) . ->* . any)
+  (((or/c txexpr? txexpr-attrs?) can-be-txexpr-attr-key?) (any/c) . ->* . any)
-  (match (assq (->txexpr-attr-key key) (get-attrs tx))
+  (match (assq (->txexpr-attr-key key) (match attrs-arg
+                                         [(? txexpr? tx) (get-attrs tx)]
+                                         [attrs attrs]))
     [(list _ value) value]
     [_ (match failure-result
          [(? procedure?) (failure-result)]
@@ -251,8 +271,7 @@
               x))))
 
 ;; function to split tag out of txexpr
-(define deleted-signal (gensym))
+(define+provide+safe (splitf-txexpr tx pred [proc (λ (x) #f)])
-(define+provide+safe (splitf-txexpr tx pred [proc (λ (x) deleted-signal)])
   ((txexpr? procedure?) (procedure?) . ->* . (values txexpr? txexpr-elements?))
   (unless (txexpr? tx)
     (raise-argument-error 'splitf-txexpr "txexpr?" tx))
@@ -263,8 +282,7 @@
        (set! matches (cons x matches))
        (proc x)]
       [(? txexpr?) (let-values ([(tag attrs elements) (txexpr->values x)]) 
-                     (txexpr-unsafe tag attrs (filter-not (λ (e) (eq? e deleted-signal))
+                     (txexpr-unsafe tag attrs (filter values (map extract! elements))))]
-                                                          (map extract! elements))))]
       [_ x]))
   (define tx-extracted (extract! tx)) ;; do this first to fill matches
   (values tx-extracted (reverse matches)))
@@ -288,15 +306,23 @@
 (define (cdata-string? x)
   (and (string? x) (regexp-match #rx"^<!\\[CDATA\\[.*\\]\\]>$" x) #true))
 
+(define comment-pattern #rx"^<!--(.*?)-->$")
+
+(define (string->comment x)
+  (match (regexp-match comment-pattern x)
+    [(list _ comment-payload) (comment comment-payload)]
+    [_ #false]))
+
 (define+provide+safe (xexpr->html x)
   (xexpr? . -> . string?)
   (xexpr->string
    (let loop ([x x])
-     (match x
+     (cond
-       [(? txexpr?)
+       [(txexpr? x)
         (define-values (tag attrs elements) (txexpr->values x))
         (define proc (if (memq tag '(script style)) ->cdata loop))
         ;; a little faster than `txexpr` since we know the pieces are valid
         (txexpr-unsafe tag attrs (map proc elements))]
-       [(? cdata-string?) (->cdata x)]
+       [(cdata-string? x) (->cdata x)]
-       [_ x]))))
+       [(and (string? x) (string->comment x))]
+       [else x]))))

txexpr/private/define-provide-safe-match.rkt

@@ -0,0 +1,82 @@
+#lang racket/base
+
+(provide define+provide+safe+match)
+
+(require racket/match
+         (for-syntax racket/base
+                     racket/syntax
+                     syntax/parse
+                     syntax/stx
+                     version/utils))
+
+;; (define+provide+safe+match name-id
+;;   contract-expr
+;;   value-expr
+;;   #:match-expander
+;;   match-transformer-expr)
+;; 
+;; (define+provide+safe+match (head . args)
+;;   contract-expr
+;;   value-body-expr
+;;   ...+
+;;   #:match-expander
+;;   match-transformer-expr)
+
+(begin-for-syntax
+  ;; Identifier -> [Syntax -> Syntax]
+  (define ((variable-like-transformer id) stx)
+    (cond
+      [(identifier? stx)
+       ; id, but with the source location of stx
+       (datum->syntax id (syntax-e id) stx id)]
+      [(stx-pair? stx)
+       (datum->syntax stx (cons id (stx-cdr stx)) stx stx)])))
+
+(define-syntax define+provide+safe+match
+  (λ (stx)
+    (syntax-parse stx
+
+      [(d (head . args)
+          contract:expr
+          value-body:expr ...+
+          #:match-expander match-transformer:expr)
+       #:with fn-expr (syntax/loc stx (λ args value-body ...))
+       (syntax/loc stx
+         (d head contract fn-expr #:match-expander match-transformer))]
+
+      [(_ name:id
+          contract:expr
+          value:expr
+          #:match-expander match-transformer:expr)
+       #:with internal-name (generate-temporary #'name)
+       #:with contract-name (generate-temporary #'name)
+       #:with make-name-match-transformer (generate-temporary #'name)
+       #:with [name-for-blame ...]
+       (cond [(version<=? "6.8" (version)) #'[#:name-for-blame name]]
+             [else                         #'[]])
+
+       #'(begin
+           (define internal-name (let ([name value]) name))
+
+           (begin-for-syntax
+             (define (make-name-match-transformer name)
+               (with-syntax ([name name]) match-transformer)))
+
+           (define-match-expander name
+             (make-name-match-transformer (quote-syntax internal-name))
+             (variable-like-transformer (quote-syntax internal-name)))
+
+           (provide name)
+
+           (module+ safe
+             (require racket/contract/base)
+
+             (define-module-boundary-contract contract-name internal-name contract
+               name-for-blame ...)
+
+             (define-match-expander name
+               (make-name-match-transformer (quote-syntax contract-name))
+               (variable-like-transformer (quote-syntax contract-name)))
+
+             (provide name)))])))
+

txexpr/scribblings/txexpr.scrbl

@@ -7,7 +7,7 @@
           (for-label racket txexpr txexpr/stx xml rackunit))
 
 @(define my-eval (make-base-eval))
-@(my-eval `(require txexpr xml rackunit))
+@(my-eval `(require racket/match txexpr xml rackunit))
 
 
 @title{txexpr: Tagged X-expressions}
@@ -195,7 +195,7 @@ Predicate for functions that handle @racket[_txexpr-attrs]. Covers values that a
 (validate-txexpr
 [possible-txexpr any/c])
 txexpr?]
-Like @racket[txexpr?], but raise a descriptive error if @racket[_possible-txexpr] is invalid, and otherwise return @racket[_possible-txexpr] itself.
+Like @racket[txexpr?], but raise a descriptive error pinpointing the first problem encountered if @racket[_possible-txexpr] is invalid, and otherwise return @racket[_possible-txexpr] itself.
 
 @examples[#:eval my-eval
 (validate-txexpr 'root)
@@ -204,6 +204,8 @@ Like @racket[txexpr?], but raise a descriptive error if @racket[_possible-txexpr
 (validate-txexpr '(root ((id "top")(class "42"))))
 (validate-txexpr '(root ((id "top")(class "42")) ("hi")))
 (validate-txexpr '(root ((id "top")(class "42")) "hi"))
+(validate-txexpr '(root (p "Hello " (span [[class "inner"]] (1 2 3)))))
+(validate-txexpr `(root (p "Look out" (span ,(void)) (1 2 3))))
 ]
 
 
@@ -229,6 +231,23 @@ Assemble a @racket[_txexpr] from its parts. If you don't have attributes, but yo
 (get-attrs tx) (get-elements tx))
 ]
 
+The @racket[txexpr] form can also be used as a match pattern:
+
+@examples[#:eval my-eval
+(match '(div)
+  [(txexpr tag attrs elems)
+   (values tag attrs elems)])
+(match '(div "Hello" (p "World"))
+  [(txexpr tag attrs elems)
+   (values tag attrs elems)])
+(match '(div "Hello" (p "World"))
+  [(txexpr 'div attrs1 (list elems1 ... (txexpr 'p attrs2 elems2)))
+   (values attrs1 elems1 attrs2 elems2)])
+(match '(div ((id "top")) "Hello" (p "World"))
+  [(txexpr 'div attrs1 (list elems1 ... (txexpr 'p attrs2 elems2)))
+   (values attrs1 elems1 attrs2 elems2)])
+]
+
 @defproc[
 (txexpr*
 [tag txexpr-tag?] 
@@ -355,19 +374,24 @@ Return @racket[#t] if @racket[_attrs] and @racket[_other-attrs] contain the same
 
 @defproc[
 (attr-ref
-[tx txexpr?]
+[attrs (or/c txexpr-attrs? txexpr?)]
 [key can-be-txexpr-attr-key?]
 [failure-result any/c (λ _ (raise (make-exn:fail:contract ....)))
 ])
 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.
+Given a @racket[_key], return the corresponding @racket[_value] from @racket[_attrs]. 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
+(define tx '(div ((id "top")(class "red")) "Hello" (p "World")))
 (attr-ref tx 'class)
 (attr-ref tx 'id)
 (attr-ref tx 'nonexistent-key)
 (attr-ref tx 'nonexistent-key "forty-two")
 (attr-ref tx 'nonexistent-key (λ _ (* 6 7)))
+(define attrs '((id "top")(class "red")))
+(attr-ref attrs 'class)
+(attr-ref attrs 'id)
+(attr-ref attrs 'nonexistent-key)
 ]
 
 @deftogether[(
@@ -456,7 +480,7 @@ In practice, most @racket[_txexpr-element]s are strings. But it's unwise to pass
 (splitf-txexpr
 [tx txexpr?]
 [pred procedure?]
-[replace-proc procedure? (λ (x) null)])
+[replace-proc procedure? (λ (x) #f)])
 (values txexpr? (listof txexpr-element?))]
 Recursively descend through @racket[_txexpr] and extract all elements that match @racket[_pred]. Returns two values: a @racket[_txexpr] with the matching elements removed, and the list of matching elements. Sort of esoteric, but I've needed it more than once, so here it is.
 

txexpr/test/contract-tests.rkt

@@ -0,0 +1,16 @@
+#lang racket/base
+
+(require (submod "../main.rkt" safe))
+(module+ test
+  (require rackunit))
+
+(module+ test
+  (check-exn (regexp (string-append
+                      "txexpr.*: contract violation\n"
+                      " *expected: txexpr-tag\\?\n"
+                      " *given: 4\n"
+                      " *in: the 1st argument.*"
+                      " *blaming: .*test/contract-tests.rkt"))
+             (λ () (txexpr 4)))
+  )
+

txexpr/test/tests.rkt

@@ -66,12 +66,85 @@
  (check-not-exn (λ _ (validate-txexpr '(p))))
  (check-not-exn (λ _ (validate-txexpr '(p "foo" "bar"))))
  (check-not-exn (λ _ (validate-txexpr '(p ((key "value")) "foo" "bar"))))
+ (check-not-exn (λ _ (validate-txexpr '(p () "foo" "bar"))))
  (check-not-exn (λ _ (validate-txexpr '(p 123)))) ; content is a valid-char
  (check-exn exn:fail? (λ _ (validate-txexpr "foo"))) ; not a list with symbol
  (check-exn exn:fail? (λ _ (validate-txexpr '(p "foo" "bar" ((key "value")))))) ; malformed
  (check-exn exn:fail? (λ _ (validate-txexpr '("p" "foo" "bar")))) ; no name
  (check-exn exn:fail? (λ _ (validate-txexpr '(root ((id "top")(class 42)))))) ; malformed attrs
- 
+ (check-exn exn:fail? (λ _ (validate-txexpr `(root  ,(void))))) ; invalid element type
+
+ (define-syntax (check-validate-exn-msg stx)
+   (syntax-case stx ()
+     [(_ tx) (syntax/loc stx (check-validate-exn-msg tx ""))]
+     [(_ tx msg) 
+      (syntax/loc stx
+        (check-equal? (with-handlers ([exn:fail:contract? (λ (e) (exn-message e))])
+                                      (validate-txexpr tx)) msg))]))
+ ;; Root element not a list
+ (check-validate-exn-msg
+  "foo"
+  "validate-txexpr: contract violation\n  expected: tagged X-expression\n  given: \"foo\"")
+
+ ;; No name
+ (check-validate-exn-msg
+  '("p" "foo" "bar")
+  "validate-txexpr: tag must be a symbol\n  tag: \"p\"\n  in: '(\"p\" \"foo\" \"bar\")")
+
+ ;; Invalid element
+ (check-validate-exn-msg
+  '(p "foo" "bar" ((key "value")))
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
+
+ ;; Malformed attribute list
+ (check-validate-exn-msg
+  '(p ((key "val") "foo" "bar") "hi")
+  "validate-txexpr: attribute is not a list of the form '(symbol \"string\")\n  attribute: \"foo\"\n  in: '(p ((key \"val\") \"foo\" \"bar\") \"hi\")")
+ 
+ ;; Invalid attribute key
+ (check-validate-exn-msg
+  '(root ((id "top") (class 42)))
+  "validate-txexpr: attribute value is not a string\n  attribute value: 42\n  in: '(root ((id \"top\") (class 42)))")
+
+ ;; Invalid attribute value
+ (check-validate-exn-msg
+  '(root ((id "top") ("class" 42)))
+  "validate-txexpr: attribute key is not a symbol\n  attribute key: \"class\"\n  in: '(root ((id \"top\") (\"class\" 42)))")
+
+ ;; Invalid element type
+ (check-validate-exn-msg
+  `(root ,(void))
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: #<void>\n  in: '(root #<void>)")
+
+ ;; (Deeply nested) No name: error should pinpoint element in 'div txexpr 
+ (check-validate-exn-msg
+  '(fine-outer [[type "valid"]] (div (br) ("p" "foo" "bar")))
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '(\"p\" \"foo\" \"bar\")\n  in: '(div (br) (\"p\" \"foo\" \"bar\"))")
+
+ ;; (Deeply nested) Invalid element: error should pinpoint element in 'p txexpr
+ (check-validate-exn-msg
+  '(fine-outer [[type "valid"]] (div (br) (p "foo" "bar" ((key "value")))))
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
+
+ ;; (Deeply nested) Malformed attribute list: error should pinpoint attr in 'p txexpr
+ (check-validate-exn-msg
+  '(fine-outer [[type "valid"]] (div (br) (p ((key "val") "foo" "bar") "hi")))
+  "validate-txexpr: attribute is not a list of the form '(symbol \"string\")\n  attribute: \"foo\"\n  in: '(p ((key \"val\") \"foo\" \"bar\") \"hi\")")
+ 
+ ;; (Deeply nested) Invalid attribute key: error should pinpoint attr key in 'p txexpr
+ (check-validate-exn-msg
+  '(fine-outer [[type "valid"]] (div (br) (p ((id "top") (class 42)))))
+  "validate-txexpr: attribute value is not a string\n  attribute value: 42\n  in: '(p ((id \"top\") (class 42)))")
+
+ ;; (Deeply nested) Invalid attribute value: error should pinpoint attr val in 'p txexpr
+ (check-validate-exn-msg
+  '(fine-outer [[type "valid"]] (div (br) (p ((id "top") ("class" 42)))))
+  "validate-txexpr: attribute key is not a symbol\n  attribute key: \"class\"\n  in: '(p ((id \"top\") (\"class\" 42)))")
+
+ ;; (Deeply nested) Invalid element type: error should pinpoint element in 'p txexpr
+ (check-validate-exn-msg
+  `(fine-outer [[type "valid"]] (div (br) (p ,(void))))
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: #<void>\n  in: '(p #<void>)")
  
  (check-txexprs-equal? (make-txexpr 'p) '(p))
  (check-txexprs-equal? (make-txexpr 'p '((key "value"))) '(p ((key "value"))))
@@ -108,6 +181,19 @@
                (txexpr->list '(p ((key "value")))))
  (check-equal? (values->list (txexpr->values '(p ((key "value")) "foo"))) 
                (txexpr->list '(p ((key "value")) "foo")))
+
+ ;; testing the match expander success
+ (check-match '(p ((key "value")) "leaf")
+              (txexpr 'p `((key ,val)) (list "leaf"))
+              (string=? val "value"))
+
+ ;; testing the match expander failure
+ (check-false (match '(p ((key "value")) "something")
+                [(txexpr 'p _ (list "else")) #true]
+                [_                           #false]))
+ (check-false (match "foo"
+                [(txexpr _ _ _) #true]
+                [_              #false]))
  
  (check-equal? (get-tag '(p ((key "value"))"foo" "bar" (em "square"))) 'p)
  (check-equal? (get-attrs '(p ((key "value"))"foo" "bar" (em "square"))) '((key "value")))
@@ -137,12 +223,18 @@
  (check-exn exn:fail? (λ _ (attr-ref '(p ((foo "bar"))) 'zam)))
  (check-equal? (attr-ref '(p ((foo "bar"))) 'zam 42) 42)
  (check-equal? (attr-ref '(p ((foo "bar"))) 'zam (λ _ (* 6 7))) 42)
+ (check-equal? (attr-ref '((foo "bar")) 'foo) "bar")
+ (check-exn exn:fail? (λ _ (attr-ref '((foo "bar")) 'zam)))
+ (check-equal? (attr-ref '((foo "bar")) 'zam 42) 42)
+ (check-equal? (attr-ref '((foo "bar")) 'zam (λ _ (* 6 7))) 42)
  (check-txexprs-equal? (attr-set '(p ((foo "bar"))) 'foo "fraw") '(p ((foo "fraw"))))
  (check-txexprs-equal? (attr-set* '(p ((foo "bar"))) 'foo "fraw") '(p ((foo "fraw"))))
  (check-true (let ([result (attr-set* '(p ((foo "bar"))) 'foo "fraw" 'zim 'zam)])
                (and (member '(foo "fraw") (get-attrs result))
                     (member '(zim "zam") (get-attrs result)) #t)))
  (check-txexprs-equal? (attr-join '(p ((foo "bar"))) 'foo "zam") '(p ((foo "bar zam"))))
+ (check-txexprs-equal? (attr-join '(tx ((foo "bar")) baz (p bin)) 'key 'val)
+                       '(tx ((foo "bar") (key "val")) baz (p bin)))
  (check-true (let ([result (attr-join '(p ((foo "bar"))) 'zim "zam")])
                (and (member '(foo "bar") (get-attrs result))
                     (member '(zim "zam") (get-attrs result)) #t)))
@@ -219,4 +311,16 @@
                "<root><script>3 > 2</script>Why is 3 &gt; 2?</root>")
 
  (check-equal? (xexpr->html '(root (div "<![CDATA[3 > 2]]>") "Why is 3 > 2?"))
-               "<root><div><![CDATA[3 > 2]]></div>Why is 3 &gt; 2?</root>"))
+               "<root><div><![CDATA[3 > 2]]></div>Why is 3 &gt; 2?</root>")
+ 
+ ;; comment
+ (check-equal? (xexpr->html '(root "<!-- comment -->" "Why is 3 > 2?"))
+               "<root><!-- comment -->Why is 3 &gt; 2?</root>")
+
+  ;; malformed comment: merged with next string
+ (check-equal? (xexpr->html '(root "<!-- comment -->Why is 3 > 2?"))
+               "<root>&lt;!-- comment --&gt;Why is 3 &gt; 2?</root>")
+
+ ;; malformed comment: missing double hyphen at end
+ (check-equal? (xexpr->html '(root "<!-- comment ->" "Why is 3 > 2?"))
+               "<root>&lt;!-- comment -&gt;Why is 3 &gt; 2?</root>"))