More namespace serialization voodoo

[xuriella.git] / xslt.lisp

;;; -*- show-trailing-whitespace: t; indent-tabs-mode: nil -*-

;;; Copyright (c) 2007,2008 David Lichteblau, Ivan Shvedunov.
;;; All rights reserved.

;;; Redistribution and use in source and binary forms, with or without
;;; modification, are permitted provided that the following conditions
;;; are met:
;;;
;;;   * Redistributions of source code must retain the above copyright
;;;     notice, this list of conditions and the following disclaimer.
;;;
;;;   * Redistributions in binary form must reproduce the above
;;;     copyright notice, this list of conditions and the following
;;;     disclaimer in the documentation and/or other materials
;;;     provided with the distribution.
;;;
;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;;; ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

(in-package :xuriella)

#+sbcl
(declaim (optimize (debug 2)))


(eval-when (:compile-toplevel :load-toplevel :execute)
  (defvar *xsl* "http://www.w3.org/1999/XSL/Transform")
  (defvar *xml* "http://www.w3.org/XML/1998/namespace")
  (defvar *html* "http://www.w3.org/1999/xhtml"))


;;;; XSLT-ERROR

(define-condition xslt-error (simple-error)
  ()
  (:documentation "The class of all XSLT errors."))

(define-condition recoverable-xslt-error (xslt-error)
  ()
  (:documentation "The class of recoverable XSLT errors."))

(defun xslt-error (fmt &rest args)
  (error 'xslt-error :format-control fmt :format-arguments args))

(defun xslt-cerror (fmt &rest args)
  (with-simple-restart (recover "recover")
    (error 'recoverable-xslt-error
           :format-control fmt
           :format-arguments args)))

(defvar *debug* nil)

(defmacro handler-case* (form &rest clauses)
  ;; like HANDLER-CASE if *DEBUG* is off.  If it's on, don't establish
  ;; a handler at all so that we see the real stack traces.  (We could use
  ;; HANDLER-BIND here and check at signalling time, but doesn't seem
  ;; important.)
  (let ((doit (gensym)))
    `(flet ((,doit () ,form))
       (if *debug*
           (,doit)
           (handler-case
               (,doit)
             ,@clauses)))))

(defun compile-xpath (xpath &optional env)
  (handler-case*
      (xpath:compile-xpath xpath env)
    (xpath:xpath-error (c)
      (xslt-error "~A" c))))

(defmacro with-stack-limit ((&optional) &body body)
  `(invoke-with-stack-limit (lambda () ,@body)))


;;;; Helper function and macro

(defun map-pipe-eagerly (fn pipe)
  (xpath::enumerate pipe :key fn :result nil))

(defmacro do-pipe ((var pipe &optional result) &body body)
  `(block nil
     (map-pipe-eagerly #'(lambda (,var) ,@body) ,pipe)
     ,result))


;;;; XSLT-ENVIRONMENT and XSLT-CONTEXT

(defparameter *namespaces*
  '((nil . "")
    ("xmlns" . #"http://www.w3.org/2000/xmlns/")
    ("xml" . #"http://www.w3.org/XML/1998/namespace")))

(defvar *global-variable-declarations*)
(defvar *lexical-variable-declarations*)

(defvar *global-variable-values*)
(defvar *lexical-variable-values*)

(defclass xslt-environment () ())

(defun split-qname (str)
  (handler-case
      (multiple-value-bind (prefix local-name)
          (cxml::split-qname str)
        (unless
            ;; FIXME: cxml should really offer a function that does
            ;; checks for NCName and QName in a sensible way for user code.
            ;; cxml::split-qname is tailored to the needs of the parser.
            ;;
            ;; For now, let's just check the syntax explicitly.
            (and (or (null prefix) (xpath::nc-name-p prefix))
                 (xpath::nc-name-p local-name))
          (xslt-error "not a qname: ~A" str))
        (values prefix local-name))
    (cxml:well-formedness-violation ()
      (xslt-error "not a qname: ~A" str))))

(defun decode-qname (qname env attributep)
  (multiple-value-bind (prefix local-name)
      (split-qname qname)
    (values local-name
            (if (or prefix (not attributep))
                (xpath-sys:environment-find-namespace env (or prefix ""))
                "")
            prefix)))

(defmethod xpath-sys:environment-find-namespace ((env xslt-environment) prefix)
  (or (cdr (assoc prefix *namespaces* :test 'equal))
      ;; zzz gross hack.
      ;; Change the entire code base to represent "no prefix" as the
      ;; empty string consistently.  unparse.lisp has already been changed.
      (and (equal prefix "")
           (cdr (assoc nil *namespaces* :test 'equal)))
      (and (eql prefix nil)
           (cdr (assoc "" *namespaces* :test 'equal)))))

(defun find-variable-index (local-name uri table)
  (position (cons local-name uri) table :test 'equal))

(defun intern-global-variable (local-name uri)
  (or (find-variable-index local-name uri *global-variable-declarations*)
      (push-variable local-name uri *global-variable-declarations*)))

(defun push-variable (local-name uri table)
  (prog1
      (length table)
    (vector-push-extend (cons local-name uri) table)))

(defun lexical-variable-value (index &optional (errorp t))
  (let ((result (svref *lexical-variable-values* index)))
    (when errorp
      (assert (not (eq result 'unbound))))
    result))

(defun (setf lexical-variable-value) (newval index)
  (assert (not (eq newval 'unbound)))
  (setf (svref *lexical-variable-values* index) newval))

(defun global-variable-value (index &optional (errorp t))
  (let ((result (svref *global-variable-values* index)))
    (when errorp
      (assert (not (eq result 'unbound))))
    result))

(defun (setf global-variable-value) (newval index)
  (assert (not (eq newval 'unbound)))
  (setf (svref *global-variable-values* index) newval))

(defmethod xpath-sys:environment-find-function
    ((env xslt-environment) lname uri)
  (if (string= uri "")
      (or (xpath-sys:find-xpath-function lname *xsl*)
          (xpath-sys:find-xpath-function lname uri))
      (xpath-sys:find-xpath-function lname uri)))

(defmethod xpath-sys:environment-find-variable
    ((env xslt-environment) lname uri)
  (let ((index
         (find-variable-index lname uri *lexical-variable-declarations*)))
    (when index
      (lambda (ctx)
        (declare (ignore ctx))
        (svref *lexical-variable-values* index)))))

(defclass lexical-xslt-environment (xslt-environment) ())

(defmethod xpath-sys:environment-find-variable
    ((env lexical-xslt-environment) lname uri)
  (or (call-next-method)
      (let ((index
             (find-variable-index lname uri *global-variable-declarations*)))
        (when index
          (xslt-trace-thunk
           (lambda (ctx)
             (declare (ignore ctx))
             (svref *global-variable-values* index))
           "global ~s (uri ~s) = ~s" lname uri :result)))))

(defclass global-variable-environment (xslt-environment)
  ((initial-global-variable-thunks
    :initarg :initial-global-variable-thunks
    :accessor initial-global-variable-thunks)))

(defmethod xpath-sys:environment-find-variable
    ((env global-variable-environment) lname uri)
  (or (call-next-method)
      (gethash (cons lname uri) (initial-global-variable-thunks env))))


;;;; TOPLEVEL-TEXT-OUTPUT-SINK
;;;;
;;;; A sink that serializes only text not contained in any element.

(defmacro with-toplevel-text-output-sink ((var) &body body)
  `(invoke-with-toplevel-text-output-sink (lambda (,var) ,@body)))

(defclass toplevel-text-output-sink (sax:default-handler)
  ((target :initarg :target :accessor text-output-sink-target)
   (depth :initform 0 :accessor textoutput-sink-depth)))

(defmethod sax:start-element ((sink toplevel-text-output-sink)
                              namespace-uri local-name qname attributes)
  (declare (ignore namespace-uri local-name qname attributes))
  (incf (textoutput-sink-depth sink)))

(defmethod sax:characters ((sink toplevel-text-output-sink) data)
  (when (zerop (textoutput-sink-depth sink))
    (write-string data (text-output-sink-target sink))))

(defmethod sax:end-element ((sink toplevel-text-output-sink)
                              namespace-uri local-name qname)
  (declare (ignore namespace-uri local-name qname))
  (decf (textoutput-sink-depth sink)))

(defun invoke-with-toplevel-text-output-sink (fn)
  (with-output-to-string (s)
    (funcall fn (make-instance 'toplevel-text-output-sink :target s))))


;;;; TEXT-FILTER
;;;;
;;;; A sink that passes through only text (at any level).

(defclass text-filter (sax:default-handler)
  ((target :initarg :target :accessor text-filter-target)))

(defmethod sax:characters ((sink text-filter) data)
  (sax:characters (text-filter-target sink) data))

(defmethod sax:end-document ((sink text-filter))
  (sax:end-document (text-filter-target sink)))

(defun make-text-filter (target)
  (make-instance 'text-filter :target target))


;;;; Names

(defun of-name (local-name)
  (stp:of-name local-name *xsl*))

(defun namep (node local-name)
  (and (typep node '(or stp:element stp:attribute))
       (equal (stp:namespace-uri node) *xsl*)
       (equal (stp:local-name node) local-name)))


;;;; PARSE-STYLESHEET

(defstruct stylesheet
  (modes (make-hash-table :test 'equal))
  (global-variables (make-empty-declaration-array))
  (output-specification (make-output-specification))
  (strip-tests nil)
  (named-templates (make-hash-table :test 'equal))
  (attribute-sets (make-hash-table :test 'equal))
  (keys (make-hash-table :test 'equal))
  (namespace-aliases (make-hash-table :test 'equal)))

(defstruct mode (templates nil))

(defun find-mode (stylesheet local-name &optional uri)
  (gethash (cons local-name uri) (stylesheet-modes stylesheet)))

(defun ensure-mode (stylesheet &optional local-name uri)
  (or (find-mode stylesheet local-name uri)
      (setf (gethash (cons local-name uri) (stylesheet-modes stylesheet))
            (make-mode))))

(defun ensure-mode/qname (stylesheet qname env)
  (if qname
      (multiple-value-bind (local-name uri)
          (decode-qname qname env nil)
        (ensure-mode stylesheet local-name uri))
      (find-mode stylesheet nil)))

(defun acons-namespaces (element &optional (bindings *namespaces*))
  (map-namespace-declarations (lambda (prefix uri)
                                (push (cons prefix uri) bindings))
                              element)
  bindings)

(defun find-key (name stylesheet)
  (or (gethash name (stylesheet-keys stylesheet))
      (xslt-error "unknown key: ~a" name)))

(defun make-key (match use) (cons match use))

(defun key-match (key) (car key))

(defun key-use (key) (cdr key))

(defun add-key (stylesheet name match use)
  (if (gethash name (stylesheet-keys stylesheet))
      (xslt-error "duplicate key: ~a" name)
      (setf (gethash name (stylesheet-keys stylesheet))
            (make-key match use))))

(defvar *excluded-namespaces* (list *xsl*))
(defvar *empty-mode*)
(defvar *default-mode*)

(defvar *xsl-include-stack* nil)

(defun uri-to-pathname (uri)
  (cxml::uri-to-pathname (puri:parse-uri uri)))

(defun parse-stylesheet-to-stp (input uri-resolver)
  (let* ((d (cxml:parse input (make-text-normalizer (cxml-stp:make-builder))))
         (<transform> (stp:document-element d)))
    (strip-stylesheet <transform>)
    ;; FIXME: handle embedded stylesheets
    (unless (and (equal (stp:namespace-uri <transform>) *xsl*)
                 (or (equal (stp:local-name <transform>) "transform")
                     (equal (stp:local-name <transform>) "stylesheet")))
      (xslt-error "not a stylesheet"))
    (dolist (include (stp:filter-children (of-name "include") <transform>))
      (let* ((uri (puri:merge-uris (stp:attribute-value include "href")
                                   (stp:base-uri include)))
             (uri (if uri-resolver
                      (funcall uri-resolver (puri:render-uri uri nil))
                      uri))
             (str (puri:render-uri uri nil))
             (pathname
              (handler-case
                  (uri-to-pathname uri)
                (cxml:xml-parse-error (c)
                  (xslt-error "cannot find included stylesheet ~A: ~A"
                              uri c)))))
        (with-open-file
            (stream pathname
                    :element-type '(unsigned-byte 8)
                    :if-does-not-exist nil)
          (unless stream
            (xslt-error "cannot find included stylesheet ~A at ~A"
                        uri pathname))
          (when (find str *xsl-include-stack* :test #'equal)
            (xslt-error "recursive inclusion of ~A" uri))
          (let* ((*xsl-include-stack* (cons str *xsl-include-stack*))
                 (<transform>2 (parse-stylesheet-to-stp stream uri-resolver)))
            (stp:insert-child-after <transform>
                                    (stp:copy <transform>2)
                                    include)
            (stp:detach include)))))
    <transform>))

(defvar *instruction-base-uri*) ;misnamed, is also used in other attributes
(defvar *apply-imports-limit*)
(defvar *import-priority*)
(defvar *extension-namespaces*)

(defmacro do-toplevel ((var xpath <transform>) &body body)
  `(map-toplevel (lambda (,var) ,@body) ,xpath ,<transform>))

(defun map-toplevel (fn xpath <transform>)
  (dolist (node (list-toplevel xpath <transform>))
    (let ((*namespaces* *namespaces*))
      (xpath:do-node-set (ancestor (xpath:evaluate "ancestor::node()" node))
        (when (xpath-protocol:node-type-p ancestor :element)
          (setf *namespaces* (acons-namespaces ancestor))))
      (funcall fn node))))

(defun list-toplevel (xpath <transform>)
  (labels ((recurse (sub)
             (let ((subsubs
                    (xpath-sys:pipe-of
                     (xpath:evaluate "transform|stylesheet" sub))))
               (xpath::append-pipes
                (xpath-sys:pipe-of (xpath:evaluate xpath sub))
                (xpath::mappend-pipe #'recurse subsubs)))))
    (xpath::sort-nodes (recurse <transform>))))

(defmacro with-parsed-prefixes ((node env) &body body)
  `(invoke-with-parsed-prefixes (lambda () ,@body) ,node ,env))

(defun invoke-with-parsed-prefixes (fn node env)
  (unless (or (namep node "stylesheet") (namep node "transform"))
    (setf node (stp:parent node)))
  (let ((*excluded-namespaces* (list *xsl*))
        (*extension-namespaces* '()))
    (parse-exclude-result-prefixes! node env)
    (parse-extension-element-prefixes! node env)
    (funcall fn)))

(defun parse-1-stylesheet (env stylesheet designator uri-resolver)
  (let* ((<transform> (parse-stylesheet-to-stp designator uri-resolver))
         (instruction-base-uri (stp:base-uri <transform>))
         (namespaces (acons-namespaces <transform>))
         (apply-imports-limit (1+ *import-priority*))
         (continuations '()))
    (let ((*namespaces* namespaces))
      (invoke-with-parsed-prefixes (constantly t) <transform> env))
    (macrolet ((with-specials ((&optional) &body body)
                 `(let ((*instruction-base-uri* instruction-base-uri)
                        (*namespaces* namespaces)
                        (*apply-imports-limit* apply-imports-limit))
                    ,@body)))
      (with-specials ()
        (do-toplevel (import "import" <transform>)
          (let ((uri (puri:merge-uris (stp:attribute-value import "href")
                                      (stp:base-uri import))))
            (push (parse-imported-stylesheet env stylesheet uri uri-resolver)
                  continuations))))
      (let ((import-priority
             (incf *import-priority*))
            (var-cont (prepare-global-variables stylesheet <transform>)))
        ;; delay the rest of compilation until we've seen all global
        ;; variables:
        (lambda ()
          (mapc #'funcall (nreverse continuations))
          (with-specials ()
            (let ((*import-priority* import-priority))
              (funcall var-cont)
              (parse-keys! stylesheet <transform> env)
              (parse-templates! stylesheet <transform> env)
              (parse-output! stylesheet <transform>)
              (parse-strip/preserve-space! stylesheet <transform> env)
              (parse-attribute-sets! stylesheet <transform> env)
              (parse-namespace-aliases! stylesheet <transform> env))))))))

(defvar *xsl-import-stack* nil)

(defun parse-imported-stylesheet (env stylesheet uri uri-resolver)
  (let* ((uri (if uri-resolver
                  (funcall uri-resolver (puri:render-uri uri nil))
                  uri))
         (str (puri:render-uri uri nil))
         (pathname
          (handler-case
              (uri-to-pathname uri)
            (cxml:xml-parse-error (c)
              (xslt-error "cannot find imported stylesheet ~A: ~A"
                          uri c)))))
    (with-open-file
        (stream pathname
                :element-type '(unsigned-byte 8)
                :if-does-not-exist nil)
      (unless stream
        (xslt-error "cannot find imported stylesheet ~A at ~A"
                    uri pathname))
      (when (find str *xsl-import-stack* :test #'equal)
        (xslt-error "recursive inclusion of ~A" uri))
      (let ((*xsl-import-stack* (cons str *xsl-import-stack*)))
        (parse-1-stylesheet env stylesheet stream uri-resolver)))))

(defun parse-stylesheet (designator &key uri-resolver)
  (xpath:with-namespaces ((nil #.*xsl*))
    (let* ((*import-priority* 0)
           (puri:*strict-parse* nil)
           (stylesheet (make-stylesheet))
           (env (make-instance 'lexical-xslt-environment))
           (*excluded-namespaces* *excluded-namespaces*)
           (*global-variable-declarations* (make-empty-declaration-array)))
      (ensure-mode stylesheet nil)
      (funcall (parse-1-stylesheet env stylesheet designator uri-resolver))
      ;; reverse attribute sets:
      (let ((table (stylesheet-attribute-sets stylesheet)))
        (maphash (lambda (k v)
                   (setf (gethash k table) (nreverse v)))
                 table))
      stylesheet)))

(defun parse-attribute-sets! (stylesheet <transform> env)
  (do-toplevel (elt "attribute-set" <transform>)
    (with-parsed-prefixes (elt env)
      (push (let* ((sets
                    (mapcar (lambda (qname)
                              (multiple-value-list (decode-qname qname env nil)))
                            (words
                             (stp:attribute-value elt "use-attribute-sets"))))
                   (instructions
                    (stp:map-children
                     'list
                     (lambda (child)
                       (unless (or (not (typep child 'stp:element))
                                   (and (equal (stp:namespace-uri child) *xsl*)
                                        (equal (stp:local-name child)
                                               "attribute"))
                                   (find (stp:namespace-uri child)
                                         *extension-namespaces*
                                         :test 'equal))
                         (xslt-error "non-attribute found in attribute set"))
                       (parse-instruction child))
                     elt))
                   (*lexical-variable-declarations*
                    (make-empty-declaration-array))
                   (thunk
                    (compile-instruction `(progn ,@instructions) env))
                   (n-variables (length *lexical-variable-declarations*)))
              (lambda (ctx)
                (with-stack-limit ()
                  (loop for (local-name uri nil) in sets do
                       (dolist (thunk (find-attribute-set local-name uri))
                         (funcall thunk ctx)))
                  (let ((*lexical-variable-values*
                         (make-variable-value-array n-variables)))
                    (funcall thunk ctx)))))
            (gethash (multiple-value-bind (local-name uri)
                         (decode-qname (stp:attribute-value elt "name") env nil)
                       (cons local-name uri))
                     (stylesheet-attribute-sets stylesheet))))))

(defun parse-namespace-aliases! (stylesheet <transform> env)
  (do-toplevel (elt "namespace-alias" <transform>)
    (stp:with-attributes (stylesheet-prefix result-prefix) elt
      (setf (gethash
             (xpath-sys:environment-find-namespace env stylesheet-prefix)
             (stylesheet-namespace-aliases stylesheet))
            (xpath-sys:environment-find-namespace
             env
             (if (equal result-prefix "#default")
                 ""
                 result-prefix))))))

(defun parse-exclude-result-prefixes! (node env)
  (stp:with-attributes (exclude-result-prefixes)
      node
    (dolist (prefix (words (or exclude-result-prefixes "")))
      (if (equal prefix "#default")
          (setf prefix nil)
          (unless (cxml-stp-impl::nc-name-p prefix)
            (xslt-error "invalid prefix: ~A" prefix)))
      (push (or (xpath-sys:environment-find-namespace env prefix)
                (xslt-error "namespace not found: ~A" prefix))
            *excluded-namespaces*))))

(defun parse-extension-element-prefixes! (node env)
  (stp:with-attributes (extension-element-prefixes)
      node
    (dolist (prefix (words (or extension-element-prefixes "")))
      (if (equal prefix "#default")
          (setf prefix nil)
          (unless (cxml-stp-impl::nc-name-p prefix)
            (xslt-error "invalid prefix: ~A" prefix)))
      (let ((uri
             (or (xpath-sys:environment-find-namespace env prefix)
                 (xslt-error "namespace not found: ~A" prefix))))
        (unless (equal uri *xsl*)
          (push uri *extension-namespaces*)
          (push uri *excluded-namespaces*))))))

(defun parse-strip/preserve-space! (stylesheet <transform> env)
  (xpath:with-namespaces ((nil #.*xsl*))
    (do-toplevel (elt "strip-space|preserve-space" <transform>)
      (let ((*namespaces* (acons-namespaces elt))
            (mode
             (if (equal (stp:local-name elt) "strip-space")
                 :strip
                 :preserve)))
        (dolist (name-test (words (stp:attribute-value elt "elements")))
          (let* ((pos (search ":*" name-test))
                 (test-function
                  (cond
                    ((eql pos (- (length name-test) 2))
                     (let* ((prefix (subseq name-test 0 pos))
                            (name-test-uri
                             (xpath-sys:environment-find-namespace env prefix)))
                       (unless (xpath::nc-name-p prefix)
                         (xslt-error "not an NCName: ~A" prefix))
                       (lambda (local-name uri)
                         (declare (ignore local-name))
                         (if (equal uri name-test-uri)
                             mode
                             nil))))
                    ((equal name-test "*")
                     (lambda (local-name uri)
                       (declare (ignore local-name uri))
                       mode))
                    (t
                     (multiple-value-bind (name-test-local-name name-test-uri)
                         (decode-qname name-test env nil)
                       (lambda (local-name uri)
                         (if (and (equal local-name name-test-local-name)
                                  (equal uri name-test-uri))
                             mode
                             nil)))))))
            (push test-function (stylesheet-strip-tests stylesheet))))))))

(defstruct (output-specification
             (:conc-name "OUTPUT-"))
  method
  indent
  omit-xml-declaration
  encoding)

(defun parse-output! (stylesheet <transform>)
  (let ((outputs (list-toplevel "output" <transform>)))
    (when outputs
      (when (cdr outputs)
        ;; FIXME:
        ;;   - concatenate cdata-section-elements
        ;;   - the others must not conflict
        (error "oops, merging of output elements not supported yet"))
      (let ((<output> (car outputs))
            (spec (stylesheet-output-specification stylesheet)))
        (stp:with-attributes (;; version
                              method
                              indent
                              encoding
;;;                           media-type
;;;                           doctype-system
;;;                           doctype-public
                              omit-xml-declaration
;;;                           standalone
;;;                           cdata-section-elements
                              )
            <output>
          (setf (output-method spec) method)
          (setf (output-indent spec) indent)
          (setf (output-encoding spec) encoding)
          (setf (output-omit-xml-declaration spec) omit-xml-declaration))))))

(defun make-empty-declaration-array ()
  (make-array 1 :fill-pointer 0 :adjustable t))

(defun make-variable-value-array (n-lexical-variables)
  (make-array n-lexical-variables :initial-element 'unbound))

(defun compile-global-variable (<variable> env) ;; also for <param>
  (stp:with-attributes (name select) <variable>
    (when (and select (stp:list-children <variable>))
      (xslt-error "variable with select and body"))
    (let* ((*lexical-variable-declarations* (make-empty-declaration-array))
           (inner (cond
                    (select
                     (compile-xpath select env))
                    ((stp:list-children <variable>)
                     (let* ((inner-sexpr `(progn ,@(parse-body <variable>)))
                            (inner-thunk (compile-instruction inner-sexpr env)))
                       (lambda (ctx)
                         (apply-to-result-tree-fragment ctx inner-thunk))))
                    (t
                     (lambda (ctx)
                       (declare (ignore ctx))
                       ""))))
           (n-lexical-variables (length *lexical-variable-declarations*)))
      (xslt-trace-thunk
       (lambda (ctx)
         (let* ((*lexical-variable-values*
                 (make-variable-value-array n-lexical-variables)))
           (funcall inner ctx)))
       "global ~s (~s) = ~s" name select :result))))

(defstruct (variable-information
             (:constructor make-variable)
             (:conc-name "VARIABLE-"))
  index
  thunk
  local-name
  uri
  param-p
  thunk-setter)

(defun parse-global-variable! (<variable> global-env) ;; also for <param>
  (let* ((*namespaces* (acons-namespaces <variable>))
         (instruction-base-uri (stp:base-uri <variable>))
         (*instruction-base-uri* instruction-base-uri)
         (*excluded-namespaces* (list *xsl*))
         (*extension-namespaces* '())
         (qname (stp:attribute-value <variable> "name")))
    (with-parsed-prefixes (<variable> global-env)
      (unless qname
        (xslt-error "name missing in ~A" (stp:local-name <variable>)))
      (multiple-value-bind (local-name uri)
          (decode-qname qname global-env nil)
        ;; For the normal compilation environment of templates, install it
        ;; into *GLOBAL-VARIABLE-DECLARATIONS*:
        (let ((index (intern-global-variable local-name uri)))
          ;; For the evaluation of a global variable itself, build a thunk
          ;; that lazily resolves other variables, stored into
          ;; INITIAL-GLOBAL-VARIABLE-THUNKS:
          (let* ((value-thunk :unknown)
                 (global-variable-thunk
                  (lambda (ctx)
                    (let ((v (global-variable-value index nil)))
                      (when (eq v 'seen)
                        (xslt-error "recursive variable definition"))
                      (cond
                        ((eq v 'unbound)
                         (setf (global-variable-value index) 'seen)
                         (setf (global-variable-value index)
                               (funcall value-thunk ctx)))
                        (t
                         v)))))
                 (excluded-namespaces *excluded-namespaces*)
                 (extension-namespaces *extension-namespaces*)
                 (thunk-setter
                  (lambda ()
                    (let ((*instruction-base-uri* instruction-base-uri)
                          (*excluded-namespaces* excluded-namespaces)
                          (*extension-namespaces* extension-namespaces))
                      (setf value-thunk
                            (compile-global-variable <variable> global-env))))))
            (setf (gethash (cons local-name uri)
                           (initial-global-variable-thunks global-env))
                  global-variable-thunk)
            (make-variable :index index
                           :local-name local-name
                           :uri uri
                           :thunk global-variable-thunk
                           :param-p (namep <variable> "param")
                           :thunk-setter thunk-setter)))))))

(defun parse-keys! (stylesheet <transform> env)
  (xpath:with-namespaces ((nil #.*xsl*))
    (do-toplevel (<key> "key" <transform>)
      (let ((*instruction-base-uri* (stp:base-uri <key>)))
        (stp:with-attributes (name match use) <key>
          (unless name (xslt-error "key name attribute not specified"))
          (unless match (xslt-error "key match attribute not specified"))
          (unless use (xslt-error "key use attribute not specified"))
          (multiple-value-bind (local-name uri)
              (decode-qname name env nil)
            (add-key stylesheet
                     (cons local-name uri)
                     (compile-xpath `(xpath:xpath ,(parse-key-pattern match)) env)
                     (compile-xpath use env))))))))

(defun prepare-global-variables (stylesheet <transform>)
  (xpath:with-namespaces ((nil #.*xsl*))
    (let* ((table (make-hash-table :test 'equal))
           (global-env (make-instance 'global-variable-environment
                                      :initial-global-variable-thunks table))
           (specs '()))
      (do-toplevel (<variable> "variable|param" <transform>)
        (let ((var (parse-global-variable! <variable> global-env)))
          (xslt-trace "parsing global variable ~s (uri ~s)"
                      (variable-local-name var)
                      (variable-uri var))
          (when (find var
                      specs
                      :test (lambda (a b)
                              (and (equal (variable-local-name a)
                                          (variable-local-name b))
                                   (equal (variable-uri a)
                                          (variable-uri b)))))
            (xslt-error "duplicate definition for global variable ~A"
                        (variable-local-name var)))
          (push var specs)))
      (setf specs (nreverse specs))
      (lambda ()
        ;; now that the global environment knows about all variables, run the
        ;; thunk setters to perform their compilation
        (mapc (lambda (spec) (funcall (variable-thunk-setter spec))) specs)
        (let ((table (stylesheet-global-variables stylesheet))
              (newlen (length *global-variable-declarations*)))
          (adjust-array table newlen :fill-pointer newlen)
          (dolist (spec specs)
            (setf (elt table (variable-index spec)) spec)))))))

(defun parse-templates! (stylesheet <transform> env)
  (let ((i 0))
    (do-toplevel (<template> "template" <transform>)
      (let ((*namespaces* (acons-namespaces <template>))
            (*instruction-base-uri* (stp:base-uri <template>)))
        (with-parsed-prefixes (<template> env)
          (dolist (template (compile-template <template> env i))
            (let ((name (template-name template)))
              (if name
                  (let* ((table (stylesheet-named-templates stylesheet))
                         (head (car (gethash name table))))
                    (when (and head (eql (template-import-priority head)
                                         (template-import-priority template)))
                      ;; fixme: is this supposed to be a run-time error?
                      (xslt-error "conflicting templates for ~A" name))
                    (push template (gethash name table)))
                  (let ((mode (ensure-mode/qname stylesheet
                                                 (template-mode-qname template)
                                                 env)))
                    (setf (template-mode template) mode)
                    (push template (mode-templates mode))))))))
      (incf i))))


;;;; APPLY-STYLESHEET

(defvar *stylesheet*)

(deftype xml-designator () '(or runes:xstream runes:rod array stream pathname))

(defun unalias-uri (uri)
  (let ((result
         (gethash uri (stylesheet-namespace-aliases *stylesheet*)
                  uri)))
    (check-type result string)
    result))

(defstruct (parameter
             (:constructor make-parameter (value local-name &optional uri)))
  (uri "")
  local-name
  value)

(defun find-parameter-value (local-name uri parameters)
  (dolist (p parameters)
    (when (and (equal (parameter-local-name p) local-name)
               (equal (parameter-uri p) uri))
      (return (parameter-value p)))))

(defvar *uri-resolver*)

(defun parse-allowing-microsoft-bom (pathname handler)
  (with-open-file (s pathname :element-type '(unsigned-byte 8))
    (unless (and (eql (read-byte s nil) #xef)
                 (eql (read-byte s nil) #xbb)
                 (eql (read-byte s nil) #xbf))
      (file-position s 0))
    (cxml:parse s handler)))

(defvar *documents*)

(defun %document (uri-string base-uri)
  (let* ((absolute-uri
          (puri:merge-uris uri-string (or base-uri "")))
         (resolved-uri
          (if *uri-resolver*
              (funcall *uri-resolver* (puri:render-uri absolute-uri nil))
              absolute-uri))
         (pathname
          (handler-case
              (uri-to-pathname resolved-uri)
            (cxml:xml-parse-error (c)
              (xslt-error "cannot find referenced document ~A: ~A"
                          resolved-uri c))))
         (xpath-root-node
          (or (gethash pathname *documents*)
              (setf (gethash pathname *documents*)
                    (make-whitespace-stripper
                     (handler-case
                         (parse-allowing-microsoft-bom pathname
                                                       (stp:make-builder))
                       ((or file-error cxml:xml-parse-error) (c)
                         (xslt-error "cannot parse referenced document ~A: ~A"
                                     pathname c)))
                     (stylesheet-strip-tests *stylesheet*))))))
    (when (puri:uri-fragment absolute-uri)
      (xslt-error "use of fragment identifiers in document() not supported"))
    xpath-root-node))

(xpath-sys:define-extension xslt *xsl*)

(defun document-base-uri (node)
  (xpath-protocol:base-uri
   (cond
     ((xpath-protocol:node-type-p node :document)
      (xpath::find-in-pipe-if
       (lambda (x)
         (xpath-protocol:node-type-p x :element))
       (xpath-protocol:child-pipe node)))
     ((xpath-protocol:node-type-p node :element)
      node)
     (t
      (xpath-protocol:parent-node node)))))

(xpath-sys:define-xpath-function/lazy
    xslt :document
    (object &optional node-set)
  (let ((instruction-base-uri *instruction-base-uri*))
    (lambda (ctx)
      (let* ((object (funcall object ctx))
             (node-set (and node-set (funcall node-set ctx)))
             (base-uri
              (if node-set
                  (document-base-uri (xpath::textually-first-node node-set))
                  instruction-base-uri)))
        (xpath-sys:make-node-set
         (if (xpath:node-set-p object)
             (xpath:map-node-set->list
              (lambda (node)
                (%document (xpath:string-value node)
                           (if node-set
                               base-uri
                               (document-base-uri node))))
              object)
             (list (%document (xpath:string-value object) base-uri))))))))

(xpath-sys:define-xpath-function/lazy xslt :key (name object)
  (let ((namespaces *namespaces*))
    (lambda (ctx)
      (let* ((qname (xpath:string-value (funcall name ctx)))
             (object (funcall object ctx))
             (expanded-name
              (multiple-value-bind (local-name uri)
                  (decode-qname/runtime qname namespaces nil)
                (cons local-name uri)))
             (key (find-key expanded-name *stylesheet*)))
        (labels ((get-by-key (value)
                   (let ((value (xpath:string-value value)))
                     (xpath::filter-pipe
                      #'(lambda (node)
                          (let ((uses
                                 (xpath:evaluate-compiled (key-use key) node)))
                            (if (xpath:node-set-p uses)
                                (xpath::find-in-pipe
                                 value
                                 (xpath-sys:pipe-of uses)
                                 :key #'xpath:string-value
                                 :test #'equal)
                                (equal value (xpath:string-value uses)))))
                      (xpath-sys:pipe-of
                       (xpath:node-set-value
                        (xpath:evaluate-compiled (key-match key) ctx)))))))
          (xpath-sys:make-node-set
           (xpath::sort-pipe
            (if (xpath:node-set-p object)
                (xpath::mappend-pipe #'get-by-key (xpath-sys:pipe-of object))
                (get-by-key object)))))))))

;; FIXME: add alias mechanism for XPath extensions in order to avoid duplication

(xpath-sys:define-xpath-function/lazy xslt :current ()
  #'(lambda (ctx)
      (xpath-sys:make-node-set
       (xpath-sys:make-pipe
        (xpath:context-starting-node ctx)
        nil))))

(xpath-sys:define-xpath-function/lazy xslt :unparsed-entity-uri (name)
  #'(lambda (ctx)
      (or (xpath-protocol:unparsed-entity-uri (xpath:context-node ctx)
                                              (funcall name ctx))
          "")))

(defun %get-node-id (node)
  (when (xpath:node-set-p node)
    (setf node (xpath::textually-first-node node)))
  (when node
    (let ((id (xpath-sys:get-node-id node))
          (highest-base-uri
           (loop
              for parent = node then next
              for next = (xpath-protocol:parent-node parent)
              for this-base-uri = (xpath-protocol:base-uri parent)
              for highest-base-uri = (if (plusp (length this-base-uri))
                                         this-base-uri
                                         highest-base-uri)
              while next
              finally (return highest-base-uri))))
      ;; Heuristic: Reverse it so that the /home/david/alwaysthesame prefix is
      ;; checked only if everything else matches.
      ;;
      ;; This might be pointless premature optimization, but I like the idea :-)
      (nreverse (concatenate 'string highest-base-uri "//" id)))))

(xpath-sys:define-xpath-function/lazy xslt :generate-id (&optional node-set-thunk)
  (if node-set-thunk
      #'(lambda (ctx)
          (%get-node-id (xpath:node-set-value (funcall node-set-thunk ctx))))
      #'(lambda (ctx)
          (%get-node-id (xpath:context-node ctx)))))

(declaim (special *available-instructions*))

(xpath-sys:define-xpath-function/lazy xslt :element-available (qname)
  (let ((namespaces *namespaces*))
    #'(lambda (ctx)
        (let ((qname (funcall qname ctx)))
          (multiple-value-bind (local-name uri)
              (decode-qname/runtime qname namespaces nil)
            (and (equal uri *xsl*)
                 (gethash local-name *available-instructions*)
                 t))))))

(xpath-sys:define-xpath-function/lazy xslt :function-available (qname)
  (let ((namespaces *namespaces*))
    #'(lambda (ctx)
        (let ((qname (funcall qname ctx)))
          (multiple-value-bind (local-name uri)
              (decode-qname/runtime qname namespaces nil)
            (and (zerop (length uri))
                 (or (xpath-sys:find-xpath-function local-name *xsl*)
                     (xpath-sys:find-xpath-function local-name uri))
                 t))))))

(defun apply-stylesheet
    (stylesheet source-designator
     &key output parameters uri-resolver navigator)
  (when (typep stylesheet 'xml-designator)
    (setf stylesheet (parse-stylesheet stylesheet)))
  (invoke-with-output-sink
   (lambda ()
     (handler-case*
         (let* ((*documents* (make-hash-table :test 'equal))
                (xpath:*navigator* (or navigator :default-navigator))
                (puri:*strict-parse* nil)
                (*stylesheet* stylesheet)
                (*empty-mode* (make-mode))
                (*default-mode* (find-mode stylesheet nil))
                (global-variable-specs
                 (stylesheet-global-variables stylesheet))
                (*global-variable-values*
                 (make-variable-value-array (length global-variable-specs)))
                (*uri-resolver* uri-resolver)
                (source-document
                 (if (typep source-designator 'xml-designator)
                     (cxml:parse source-designator (stp:make-builder))
                     source-designator))
                (xpath-root-node
                 (make-whitespace-stripper
                  source-document
                  (stylesheet-strip-tests stylesheet)))
                (ctx (xpath:make-context xpath-root-node)))
           (when (pathnamep source-designator)
             (setf (gethash source-designator *documents*) xpath-root-node))
           (map nil
                (lambda (spec)
                  (when (variable-param-p spec)
                    (let ((value
                           (find-parameter-value (variable-local-name spec)
                                                 (variable-uri spec)
                                                 parameters)))
                      (when value
                        (setf (global-variable-value (variable-index spec))
                              value)))))
                global-variable-specs)
           (map nil
                (lambda (spec)
                  (funcall (variable-thunk spec) ctx))
                global-variable-specs)
           ;; zzz we wouldn't have to mask float traps here if we used the
           ;; XPath API properly.  Unfortunately I've been using FUNCALL
           ;; everywhere instead of EVALUATE, so let's paper over that
           ;; at a central place to be sure:
           (xpath::with-float-traps-masked ()
             (apply-templates ctx :mode *default-mode*)))
       (xpath:xpath-error (c)
                          (xslt-error "~A" c))))
   (stylesheet-output-specification stylesheet)
   output))

(defun find-attribute-set (local-name uri)
  (or (gethash (cons local-name uri) (stylesheet-attribute-sets *stylesheet*))
      (xslt-error "no such attribute set: ~A/~A" local-name uri)))

(defun apply-templates/list (list &key param-bindings sort-predicate mode)
  (when sort-predicate
    (setf list (sort list sort-predicate)))
  (let* ((n (length list))
         (s/d (lambda () n)))
    (loop
       for i from 1
       for child in list
       do
         (apply-templates (xpath:make-context child s/d i)
                          :param-bindings param-bindings
                          :mode mode))))

(defvar *stack-limit* 200)

(defun invoke-with-stack-limit (fn)
  (let ((*stack-limit* (1- *stack-limit*)))
    (unless (plusp *stack-limit*)
      (xslt-error "*stack-limit* reached; stack overflow"))
    (funcall fn)))

(defun invoke-template (ctx template param-bindings)
  (let ((*lexical-variable-values*
         (make-variable-value-array (template-n-variables template))))
    (with-stack-limit ()
      (loop
         for (name-cons value) in param-bindings
         for (nil index nil) = (find name-cons
                                     (template-params template)
                                     :test #'equal
                                     :key #'car)
         do
           (when index
             (setf (lexical-variable-value index) value)))
      (funcall (template-body template) ctx))))

(defun apply-default-templates (ctx mode)
  (let ((node (xpath:context-node ctx)))
    (cond
      ((or (xpath-protocol:node-type-p node :processing-instruction)
           (xpath-protocol:node-type-p node :comment)))
      ((or (xpath-protocol:node-type-p node :text)
           (xpath-protocol:node-type-p node :attribute))
       (write-text (xpath-protocol:node-text node)))
      (t
       (apply-templates/list
        (xpath::force
         (xpath-protocol:child-pipe node))
        :mode mode)))))

(defvar *apply-imports*)

(defun apply-applicable-templates (ctx templates param-bindings finally)
  (labels ((apply-imports (&optional actual-param-bindings)
             (if templates
                 (let* ((this (pop templates))
                        (low (template-apply-imports-limit this))
                        (high (template-import-priority this)))
                   (setf templates
                         (remove-if-not
                          (lambda (x)
                            (<= low (template-import-priority x) high))
                          templates))
                   (invoke-template ctx this actual-param-bindings))
                 (funcall finally))))
    (let ((*apply-imports* #'apply-imports))
      (apply-imports param-bindings))))

(defun apply-templates (ctx &key param-bindings mode)
  (apply-applicable-templates ctx
                              (find-templates ctx (or mode *default-mode*))
                              param-bindings
                              (lambda ()
                                (apply-default-templates ctx mode))))

(defun call-template (ctx name &optional param-bindings)
  (apply-applicable-templates ctx
                              (find-named-templates name)
                              param-bindings
                              (lambda ()
                                (error "cannot find named template: ~s"
                                       name))))

(defun find-templates (ctx mode)
  (let* ((matching-candidates
          (remove-if-not (lambda (template)
                           (template-matches-p template ctx))
                         (mode-templates mode)))
         (npriorities
          (if matching-candidates
              (1+ (reduce #'max
                          matching-candidates
                          :key #'template-import-priority))
              0))
         (priority-groups (make-array npriorities :initial-element nil)))
    (dolist (template matching-candidates)
      (push template
            (elt priority-groups (template-import-priority template))))
    (loop
       for i from (1- npriorities) downto 0
       for group = (elt priority-groups i)
       for template = (maximize #'template< group)
       when template
       collect template)))

(defun find-named-templates (name)
  (gethash name (stylesheet-named-templates *stylesheet*)))

(defun template< (a b)                  ;assuming same import priority
  (let ((p (template-priority a))
        (q (template-priority b)))
    (cond
      ((< p q) t)
      ((> p q) nil)
      (t
       (xslt-cerror "conflicting templates:~_~A,~_~A"
                    (template-match-expression a)
                    (template-match-expression b))
       (< (template-position a) (template-position b))))))

(defun maximize (< things)
  (when things
    (let ((max (car things)))
      (dolist (other (cdr things))
        (when (funcall < max other)
          (setf max other)))
      max)))

(defun template-matches-p (template ctx)
  (find (xpath:context-node ctx)
        (xpath:all-nodes (funcall (template-match-thunk template) ctx))))

(defun invoke-with-output-sink (fn output-spec output)
  (etypecase output
    (pathname
     (with-open-file (s output
                        :direction :output
                        :element-type '(unsigned-byte 8)
                        :if-exists :rename-and-delete)
       (invoke-with-output-sink fn output-spec s)))
    ((or stream null)
     (invoke-with-output-sink fn
                              output-spec
                              (make-output-sink output-spec output)))
    ((or hax:abstract-handler sax:abstract-handler)
     (with-xml-output output
       (funcall fn)))))

(defun make-output-sink (output-spec stream)
  (let* ((ystream
          (if stream
              (let ((et (stream-element-type stream)))
                (cond
                  ((or (null et) (subtypep et '(unsigned-byte 8)))
                   (runes:make-octet-stream-ystream stream))
                  ((subtypep et 'character)
                   (runes:make-character-stream-ystream stream))))
              (runes:make-rod-ystream)))
         (omit-xml-declaration-p
          (equal (output-omit-xml-declaration output-spec) "yes"))
         (sax-target
          (make-instance 'cxml::sink
                         :ystream ystream
                         :omit-xml-declaration-p omit-xml-declaration-p)))
    (cond
      ((equalp (output-method output-spec) "HTML")
       (make-instance 'combi-sink
                      :hax-target (make-instance 'chtml::sink
                                                 :ystream ystream)
                      :sax-target sax-target
                      :encoding (output-encoding output-spec)))
      ((equalp (output-method output-spec) "TEXT")
       (make-text-filter sax-target))
      (t
       sax-target))))

(defstruct template
  match-expression
  match-thunk
  name
  import-priority
  apply-imports-limit
  priority
  position
  mode
  mode-qname
  params
  body
  n-variables)

(defun expression-priority (form)
  (let ((step (second form)))
    (if (and (null (cddr form))
             (listp step)
             (member (car step) '(:child :attribute))
             (null (cddr step)))
        (let ((name (second step)))
          (cond
            ((or (stringp name)
                 (and (consp name)
                      (or (eq (car name) :qname)
                          (eq (car name) :processing-instruction))))
             0.0)
            ((and (consp name)
                  (or (eq (car name) :namespace)
                      (eq (car name) '*)))
             -0.25)
            (t
             -0.5)))
        0.5)))

(defun valid-expression-p (expr)
  (cond
    ((atom expr) t)
    ((eq (first expr) :path)
     (every (lambda (x)
              (let ((filter (third x)))
                (or (null filter) (valid-expression-p filter))))
            (cdr expr)))
    ((eq (first expr) :variable)        ;(!)
     nil)
    (t
     (every #'valid-expression-p (cdr expr)))))

(defun parse-xpath (str)
  (handler-case
      (xpath:parse-xpath str)
    (xpath:xpath-error (c)
      (xslt-error "~A" c))))

;; zzz also use naive-pattern-expression here?
(defun parse-key-pattern (str)
  (let ((parsed
         (mapcar #'(lambda (item)
                     `(:path (:root :node)
                             (:descendant-or-self *)
                             ,@(cdr item)))
                 (parse-pattern str))))
    (if (null (rest parsed))
        (first parsed)
        `(:union ,@parsed))))

(defun parse-pattern (str)
  ;; zzz check here for anything not allowed as an XSLT pattern
  ;; zzz can we hack id() and key() here?
  (let ((form (parse-xpath str)))
    (unless (consp form)
      (xslt-error "not a valid pattern: ~A" str))
    (labels ((process-form (form)
               (cond ((eq (car form) :union)
                      (alexandria:mappend #'process-form (rest form)))
                     ((not (or (eq (car form) :path)
                               (and (eq (car form) :filter)
                                    (let ((filter (second form)))
                                      (and (consp filter)
                                           (member (car filter)
                                                   '(:key :id))))
                                    (equal (third form) '(:true)))
                               (member (car form) '(:key :id))))
                      (xslt-error "not a valid pattern: ~A ~A" str form))
                     ((not (valid-expression-p form))
                      (xslt-error "invalid filter"))
                     (t (list form)))))
      (process-form form))))

(defun naive-pattern-expression (x)
  (ecase (car x)
    (:path `(:path (:ancestor-or-self :node) ,@(cdr x)))
    ((:filter :key :id) x)))

(defun compile-value-thunk (value env)
  (if (and (listp value) (eq (car value) 'progn))
      (let ((inner-thunk (compile-instruction value env)))
        (lambda (ctx)
          (apply-to-result-tree-fragment ctx inner-thunk)))
      (compile-xpath value env)))

(defun compile-var-bindings/nointern (forms env)
  (loop
    for (name value) in forms
    collect (multiple-value-bind (local-name uri)
                (decode-qname name env nil)
              (list (cons local-name uri)
                    (xslt-trace-thunk
                     (compile-value-thunk value env)
                     "local variable ~s = ~s" name :result)))))

(defun compile-var-bindings (forms env)
  (loop
     for (cons thunk) in (compile-var-bindings/nointern forms env)
     for (local-name . uri) = cons
     collect (list cons
                   (push-variable local-name
                                  uri
                                  *lexical-variable-declarations*)
                   thunk)))

(defun compile-template (<template> env position)
  (stp:with-attributes (match name priority mode) <template>
    (unless (or name match)
      (xslt-error "missing match in template"))
    (multiple-value-bind (params body-pos)
        (loop
          for i from 0
          for child in (stp:list-children <template>)
          while (namep child "param")
          collect (parse-param child) into params
          finally (return (values params i)))
      (let* ((*lexical-variable-declarations* (make-empty-declaration-array))
             (param-bindings (compile-var-bindings params env))
             (body (parse-body <template> body-pos (mapcar #'car params)))
             (body-thunk (compile-instruction `(progn ,@body) env))
             (outer-body-thunk
              (xslt-trace-thunk
               #'(lambda (ctx)
                   (unwind-protect
                       (progn
                         ;; set params that weren't initialized by apply-templates
                         (loop for (name index param-thunk) in param-bindings
                               when (eq (lexical-variable-value index nil) 'unbound)
                                 do (setf (lexical-variable-value index)
                                          (funcall param-thunk ctx)))
                         (funcall body-thunk ctx))))
               "template: match = ~s name = ~s" match name))
             (n-variables (length *lexical-variable-declarations*)))
        (append
         (when name
           (multiple-value-bind (local-name uri)
               (decode-qname name env nil)
             (list
              (make-template :name (cons local-name uri)
                             :import-priority *import-priority*
                             :apply-imports-limit *apply-imports-limit*
                             :params param-bindings
                             :body outer-body-thunk
                             :n-variables n-variables))))
         (when match
           (mapcar (lambda (expression)
                     (let ((match-thunk
                            (xslt-trace-thunk
                             (compile-xpath
                              `(xpath:xpath
                                ,(naive-pattern-expression expression))
                              env)
                             "match-thunk for template (match ~s): ~s --> ~s"
                             match expression :result))
                           (p (if priority
                                  (parse-number:parse-number priority)
                                  (expression-priority expression))))
                       (make-template :match-expression expression
                                      :match-thunk match-thunk
                                      :import-priority *import-priority*
                                      :apply-imports-limit *apply-imports-limit*
                                      :priority p
                                      :position position
                                      :mode-qname mode
                                      :params param-bindings
                                      :body outer-body-thunk
                                      :n-variables n-variables)))
                   (parse-pattern match))))))))
#+(or)
(xuriella::parse-stylesheet #p"/home/david/src/lisp/xuriella/test.xsl")