@@@ mess!

[sod] / doc / misc.tex

%%% -*-latex-*-
%%%
%%% Miscellaneous functionality
%%%
%%% (c) 2015 Straylight/Edgeware
%%%

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\chapter{Miscellaneous functionality} \label{ch:misc}

%%%--------------------------------------------------------------------------
\section{Utilities} \label{sec:misc.utilities}

These symbols are defined in the @|sod-utilities| package.


\subsection{Macro utilities}

We begin with some simple utilities which help with writing macros.  Several
of these are standard.

\begin{describe}{mac}
    {with-gensyms (@{ @<var> @! (@<var> @[@<name>@]) @}^*)      \\ \ind
      @<declaration>^*                                          \\
      @<form>^*
     \-\nlret @<value>^*}
  Bind each @<var> (a symbol, not evaluated) to a freshly made gensym whose
  name is based on the corresponding @<name> (a string, evaluated), and
  evaluate the @<form>s as an implicit @|progn| in the resulting environment.
  If @<name> is omitted, then the name of the @<var> is used as a default; a
  bare symbol may be written in place of a singleton list.
\end{describe}

\begin{describe}{mac}
    {once-only (@[[ :environment @<env> @]]
                @{ @<var> @! (@<var> @[@<value-form>@]) @}^*)   \\ \ind
      @<declaration>^*                                          \\
      @<form>^*
     \-\nlret @<result-form>}
  This is a helper to ensure that macro expansions evaluate their arguments
  exactly once each, in the correct order.

  Each @<var> is bound to an appropriate value (often a gensym) and then the
  @<form>s are evaluated as an implicit @|progn| in the resulting environment
  to produce an output form.  This output form is then enclosed in one or
  more binding forms to produce a @<result-form>.  When the @<result-form> is
  evaluated, the behaviour will be as if each @<value-form> is evaluated
  exactly once each, in order, and each value is captured in the
  corresponding @<var>.

  A simple @|once-only| expansion might look something like
  \begin{prog}
    (let (\=(@<var>_1 (gensym))                                 \\
          \>\qquad\vdots                                        \\
          \>(@<var>_n (gensym)))                                \\ \ind
      `(let (\=(,@<var>_1 ,@<value-form>_1)                     \\
             \>\qquad\vdots                                     \\
             \>(,@<var>_n ,@<value-form>_n))                    \\ \ind
         @<declaration>_1 \dots\ @<declaration>_m               \\
         @<form>_1 \dots\ @<form>_\ell))
  \end{prog}
  However, if @|once-only| can determine that some @<value-form> is a
  constant (e.g., it is @|quote|d, self-evaluating, or reported as
  @|constantp| in the given environment @<env>), then it need not allocate a
  gensym: it can instead bind the @<var> directly to the constant value.

  If a @<value-form> is omitted, then the value of the corresponding @<var>
  is used.  It is conventional usage for a macro to wrap @|once-only| around
  its body so as to convert the arguments which it should evaluate into safe
  gensyms capturing their runtime values.  (Note that the simple expansion
  given above can't do this correctly.)  A bare symbol may be written in
  place of a singleton list.
\end{describe}

\begin{describe}{fun}
    {parse-body @<body> \&key :docp :declp
      @> @<doc-string> @<declarations> @<body-forms>}
  Parse the @<body> into a @<doc-string>, some @<declaration>s, and a list of
  @<body-forms>.

  The @<body> is assumed to have the general syntax
  \begin{prog}
    @[[ @<doc-string> @! @<declaration>^* @]]                   \\
    @<form>^*
  \end{prog}
  A @<doc-string> is permitted if and only if @<docp> is non-nil, and
  declarations are permitted if and only if @<declp> is non-nil; both are
  true by default.

  Each return value is a list, which is empty if the corresponding part of
  the input @<body> is missing.  Specifically:
  \begin{itemize}
  \item @<doc-string> is either nil, or a singleton list containing a string;
  \item @<declarations> is either nil, or a singleton list containing a
    @|(declare \dots)| form gathering up all of the individual
    @<declaration>s within the @<body>; and
  \item @<body-forms> is a list of the remaining forms in the @<body>.
  \end{itemize}
  Thus, the parsed body-parts can conveniently be spliced into a macro
  expansion using @|,@@|.
\end{describe}

\begin{describe}{fun}{symbolicate \&rest @<symbols> @> @<symbol>}
  Return the symbol, interned in the current @|*package*|, whose name is the
  concatenation of the names of the given @<symbols>.
\end{describe}


\subsection{Locatives}

A \emph{locative} is a value which remembers where another value is stored,
-- whether it's in a variable, an array element, a structure slot, a hash
table, etc.\ -- and can modify and retrieve it.

Some Lisp systems have highly efficient locatives which actually keep track
of the machine addresses of the places to which they refer.  Common Lisp does
not implement true locatives of this kind, but something sufficiently useful
can be synthesized.

These locatives can't usefully be compared.  It should be possible to compare
true locatives, such that two locatives compare equal if and only if they
refer to the same place; but that doesn't work for these locatives.

\begin{describe}{cls}{locative}
  The type of locative objects.
\end{describe}

\begin{describe}{fun}{locativep @<object> @> @<generalized-boolean>}
  Return non-nil if and only if @<object> is a locative.
\end{describe}

\begin{describe}{mac}{locf @<place> @> @<locative>}
  Return a fresh locative capturing the @<place>, which may be any expression
  usable as the first operand to @|setf|.
\end{describe}

\begin{describe*}
    {\dhead{fun}{ref @<locative> @> @<value>}
     \dhead{fun}{setf (ref @<locative>) @<value>}}
  Retrieve and return the current value stored in the place captured by the
  @<locative>.  With @|setf|, store the new @<value> in the place captured by
  the @<locative>.
\end{describe*}

\begin{describe}{mac}
    {with-locatives
        @{ @<var> @! (@{ @<var> @!
                         (@<var> @[@<locative>@]) @}^*) @}      \\ \ind
      @<declaration>^*                                          \\
      @<form>^*
     \-\nlret @<values>^*}
  This is a macro which hides the use of locatives from its caller using
  symbol-macros.

  Each @<locative> should be an expression which evaluates to a locative
  value (not a general place).  These are evaluated once each, left to
  right.  The @<form>s are then evaluated as an implicit @|progn|, with each
  @<var> defined as a symbol macro which will retrieve -- or, with @|setf|,
  modify -- the value referred to by the corresponding locative.

  If a @<locative> is omitted, it defaults to the value of @<var>; a
  bare symbol may be used in place of a singleton list.
\end{describe}


\subsection{Anaphorics}

An anaphoric macro implicitly binds a well-known name to a value of interest,
in the course of doing something else.  The concept was popularized by Paul
Graham \cite{graham-1993:on-lisp}.

The macros described here all bind the variable @|it|.

\begin{describe}{sym}{it}
  The symbol @|it| is exported by the @|sod-utilities| package.
\end{describe}

\begin{describe}{mac}
    {aif @<condition> @<consequent> @[@<alternative>@] @> @<value>^*}
  Evaluate the @<condition>.  If @<condition> is non-nil, then bind @|it| to
  the resulting value and evaluate the @<consequent>, returning all of its
  values.  Otherwise, evaluate @<alternative>, returning all of its values.
\end{describe}

\begin{describe}{mac}{aand @<form>^* @> @<value>^*}
  Evaluate each @<form> in turn.  If any @<form> evaluates to nil, then stop
  and return nil.  Each form except the first is evaluated with @|it| bound
  to the (necessarily non-nil) value of the previous form.  If all but the
  last form evaluate non-nil, then return all the values of the final form.
\end{describe}

(No @|aor| is provided, since @|it| would necessarily be bound to nil.)

\begin{describe}{mac}{awhen @<condition> @<form>^* @> nil}
  If @<condition> evaluates to a non-nil value, bind @|it| to that value, and
  evaluate the @<form>s as an implicit @|progn|.  Otherwise, return nil.
\end{describe}

\begin{describe}{mac}{acond @{ (@<condition> @<form>^*) @}^* @> @<value>^*}
  Evaluate each @<condition> in turn, until one of them produces a non-nil
  value.  If the @<condition> is followed by one or more @<form>s, then bind
  @|it| to the non-nil value of the @<condition> and evaluate the @<form>s as
  an implicit @|progn|; otherwise, simply return the value of the
  @<condition>.  If no @<condition> produces a non-nil value then return nil.
\end{describe}

\begin{describe*}
    {\dhead{mac}{acase @<scrutinee>
                  @{ (@{ @<case> @! (@<case>^*) @} @<form>^*) @}^*
                  @> @<value>^*}
     \dhead{mac}{aecase @<scrutinee>
                  @{ (@{ @<case> @! (@<case>^*) @} @<form>^*) @}^*
                  @> @<value>^*}
     \dhead{mac}{atypecase @<scrutinee> @{ (@<type> @<form>^*) @}^*
                  @> @<value>^*}
     \dhead{mac}{aetypecase @<scrutinee> @{ (@<type> @<form>^*) @}^*
                  @> @<value>^*}}
  These are like the Common Lisp macros @|case|, @|ecase|, @|typecase|, and
  @|etypecase|, except that @|it| is bound to the value of the @<scrutinee>
  while evaluating the matching @<form>s.
\end{describe*}

\begin{describe}{mac}{asetf @{ @<place> @<value> @}^* @> @<value>^*}
  For each @<place> and @<value> in turn: bind @|it| to the current value of
  the @<place>, evaluate the @<value> expression, and store the resulting
  value back in the @<place>.  Return the @<value>(s) stored by the final
  pair: there may be more than one value, e.g., if @<place> is a @|values|
  form.

  For example, @|(asetf @<place> (1+ it))| is almost equivalent to @|(incf
  @<place>)|, even if evaluating @<place> has side-effects.
\end{describe}


\subsection{Metaobject protocol utilities}

The following utilities make use of the introspection features of the CLOS
metaobject protocol.

\begin{describe}{gf}{instance-initargs @<instance> @> @<initargs-list>}
  Return a fresh list of plausible initargs for the given @<instance>.

  The default method should work for most classes, but may be overridden to
  cope with special effects.

  \begin{describe}{meth}{standard-object}
      {instance-initargs (@<instance> standard-object) @> @<initargs-list>}
    The default method works by digging through the instance's class's slot
    definitions and enquiring about their initargs.  Initargs which are
    handled by methods on @|shared-initialize| or similar generic functions
    won't be discovered.
  \end{describe}
\end{describe}

\begin{describe*}
    {\dhead{fun}{copy-instance @<instance> \&rest @<initargs>
                  @> @<new-instance>}
     \dhead{gf}{copy-instance-using-class @<class> @<instance>
                                          \&rest @<initargs>
                  @> @<new-instance>}}
  The @|copy-instance| function creates and returns a fresh copy of a given
  @<instance>, possibly modifying it according to the given @<initargs>.

  It immediately calls @|copy-instance-using-class|, calling it with the
  instance's class and the instance itself, and simply returns the result of
  that generic function.

  The default method on @|copy-instance-using-class| should work for most
  classes, but may be overridden to cope with special effects.

  \begin{describe}{meth}{standard-class}
    {copy-instance-using-class \=(@<class> standard-class) @<instance> \\
                               \>\&rest initargs
        \nlret @<new-instance>}
    The default method works as follows.
    \begin{enumerate}
    \item Allocate a fresh instance of @<class>, using @|allocate-instance|.
    \item For each slot defined by @<class>, if that slot is bound in the
      original instance, then set the corresponding slot in the new instance
      to the same value.
    \item Call @|shared-initialize| on the new instance, providing it the
      given list of @<initargs>, but inhibiting the usual initialization of
      slots from their initforms.
    \item Return the new instance.
    \end{enumerate}
  \end{describe}
\end{describe*}

\begin{describe}{fun}
    {find-eql-specialized-method @<function> @<arg> @<objcet>}
  Find and return a method defined on a generic @<function> whose @<arg>th
  argument (counting from zero) is @|eql|-specialized on the givan
  @<object>.  If there is no such method on @<function> then return @|nil|.
  If there are multiple such methods, return one of them arbitrarily.
\end{describe}

\begin{describe*}
    {\dhead{gf}{generic-function-methods @<generic-function> @> @<list>}
     \dhead{gf}{method-specializers @<method> @> @<list>}
     \dhead{cls}{eql-specializer}
     \dhead{gf}{eql-specializer-object @<specializer> @> @<value>}}
  These are precisely the MOP functions and class: the symbols are
  re-exported for portability, because different Lisp systems define these
  symbols in different packages.
\end{describe*}


\subsection{Other CLOS utilities}

Some other minor CLOS utilities.

\begin{describe}{mac}
    {default-slot (@<instance> @<slot> @[@<slot-names>@])       \\ \ind
      @<form>^*}
  This macro is useful in methods (usually @|:after| methods) on
  @|shared-initialize|, to set slots to some sensible default values in the
  case where no suitable initarg was given, and default initialization is too
  complicated to be done using an initform.

  Set a slot to a default value, obeying the @|shared-initialize| protocol.
  If (a) the named @<slot> of @<instance> is unbound, and (b) either
  @<slot-names> is @|t|, or @<slot> is a member of the list @<slot-names>,
  then evaluate the @<form>s as an implicit @|progn| and store their
  value in the @<slot>.  Otherwise do nothing.

  The @<instance>, @<slot>, and @<slot-names> (if any) are evaluated once
  each, left-to-right.
\end{describe}

\begin{describe}{mac}
    {define-on-demand-slot @<class> @<slot> (@<instance>)       \\ \ind
      @[[ @<declaration>^* @! @<doc-string> @]]                 \\
      @<form>^*}
  This macro makes slots with delayed initialization: rather than being
  set when the object is constructed, the slot's initial value is only
  calculated when it's first requested.  This is useful if calculating the
  slot value is expensive and often not required, or if it's not possible to
  initialize the slot along with the rest of the object because of dependency
  cycles.

  The macro arranges things as follows.  Whenever @|slot-value| is called
  (possibly indirectly, via a reader function) to read the named @<slot> (a
  symbol, not evaluated) on an (indirect) instance of @<class>, but the slot
  is unbound, then @<instance> is bound to the instance in question and the
  @<form>s are evaluated as an implicit @|progn| within the lexical
  environment of the @|define-on-demand-slot| call, and the resulting value
  is used as the initial value of the slot.  (Furthermore, a block named
  @<slot> is wrapped around the @<form>s, allowing an early return if that
  should be useful.)

  This macro currently works by defining a method on @|slot-unbound|.
\end{describe}


\subsection{Building lists}

Many Lisp functions end up constructing lists.  In simple cases, a function
like @|mapcar| will just do the job directly.  In more complex cases, a
common idiom is to build the list using @|push| for each element in turn; but
a list built this way ends up in the wrong order, so an additional pass,
usually using @|nreverse|, is necessary to fix it.

A `list builder' is an object which can be used to construct a list in the
right order.  (Currently, a list-builder is simply a cons cell, whose cdr
points to the first cons-cell of the list, and whose car points to its last
cons; an empty list-builder is a cons whose cdr is nil and whose car is the
cons itself, i.e., @|\#1=(\#1\# . nil)|.)

\begin{describe}{fun}{make-list-builder \&optional @<initial> @> @<builder>}
  Return a fresh new list-builder, initially containing no items.
\end{describe}

\begin{describe}{fun}{lbuild-add @<builder> @<item> @> @<builder>}
  Add @<item> to the end of the list being constructed in @<builder>.
\end{describe}

\begin{describe}{fun}{lbuild-add-list @<builder> @<list> @> @<builder>}
  Append @<list> to the list being constructed in @<builder>.  The list is
  \emph{not} copied: adding further items to the list will clobber cdr of its
  final cons-cell.
\end{describe}

\begin{describe}{fun}{lbuild-list @<builder> @> @<list>}
  Return the list being constructed in the @<builder>.

  It is permitted to continue adding items to the list: this will mutate the
  list in-place.  Often, this is what you want.  For example, one might write
  an analogue to @|pushnew| like this:
  \begin{prog}
    (defun lbuild-add-new
        (builder item \&key key test test-not \&rest keywords)  \\ \ind
      (declare (ignore key test test-not))                      \\
      (when (apply \#'member item (lbuild-list builder)
                   keywords)                                    \\ \ind
        (lbuild-add builder item)))
  \end{prog}
\end{describe}


\subsection{Merging lists}

The following machinery merges lists representing a partial order.  The
primary use for this is in computing class precedence lists during class
finalization.  By building the input lists and choosing the tie-breaking
@<pick> function appropriately, many different linearization algorithms can
be implemented fairly easily using @|merge-lists| below.

\begin{describe*}
    {\dhead{cls}
       {inconsistent-merge-error (error) \&key :candidates :present}
     \dhead{gf}{merge-error-candidates @<error> @> @<list>}
     \dhead{gf}{merge-error-present-function @<error> @> @<function>}}
  The @|inconsistent-merge-error| condition class used to represent a failure
  of the \descref{fun}{merge-lists}[function].

  The @<candidates> are a list of offending items from the input lists, in
  some order: the error is reporting that the function has failed because it
  is not possible to order the items listed in @<candidates> in any way
  without being inconsistent with at least one of the input lists.  There is
  no default.

  The @<present> function is used to convert the input items into
  human-readable descriptions (printed using @|princ|); the default is
  @|identity|, which will simply print the items in a `friendly' format.
  (Using @|prin1-to-string| would print their machine-readable escaped forms
  instead.)

  The functions @|merge-error-candidates| and @|merge-error-present-function|
  respectively retrieve the candidates list and presentation function
  assigned to a condition when it was created.
\end{describe*}

\begin{describe}{fun}
    {merge-lists @<lists> \&key :pick :test :present @> @<list>}
  Return a merge of the @<lists>, considered as partial orderings.

  In more detail: @<lists> should be a list of lists.  Each distinct item, as
  determined by the @<test> function (by default, @|eql|) appears in the
  result list exactly once.  Furthermore, if, in some input list, an item $x$
  appears earlier than a different item $y$, then $x$ will also precede $y$
  in the output list.

  If the input lists contradict each other (e.g., list $A$ has $x$ before
  $y$, but list $B$ has $y$ before $x$), then an error of type
  @|inconsistent-merge-error| is signalled, with the offending items attached
  as candidates, and the function @<present> (by default, @|identity|) as the
  presentation function.

  Frequently, a collection of input lists has multiple valid merges.
  Whenever @|merge-lists| must decide between two or more equally good
  candidates, it calls the @<pick> function to choose one of them.
  Specifically, it invokes @|(funcall @<pick> @<candidates>
  @<merge-so-far>)|, where @<candidates> are the items it needs to choose
  between, and @<merge-so-far> is the currently determined prefix of the
  final merge.  The order of items in the @<candidates> list reflects their
  order in the input lists: item $x$ precedes item $y$ in @<candidates> if
  any only if an occurrence of $x$ appears in an earlier input list than
  $y$.  (This completely determines the order of candidates: if two items
  appear in the same list, then that list would have ordered them and we
  wouldn't have to call @<pick> to break the tie.)  The default @<pick>
  function simply chooses the item appearing in the earliest list, i.e.,
  effectively
  \begin{prog}
    (lambda (candidates merge-so-far)                           \\ \ind
      (declare (ignore merge-so-far))                           \\
      (car candidates))
  \end{prog}
\end{describe}


\subsection{Other list utilities}

\begin{describe}{fun}
    {mappend @<function> @<list> \&rest @<more-lists> @> @<result-list>}
  Return the result of appending @<list> and @<more-lists>, in order.  All
  but the final list are copied into the @<result-list>; the last one is used
  as-is.
\end{describe}

\begin{describe}{mac}
    {categorize (\=@<item-var> @<items>
                   @[[ :bind (@{ @<var> @!
                                 (@<var> @[@<value>@]) @}^*) @]])
                                                                \\ \ind\ind
        (@{ (@<cat-var> @<cat-predicate>) @}^*)               \-\\
      @<declaration>^*                                          \\
      @<form>^*
     \-\nlret @<value>^*}
  Partition an input list of @<items> according to the @<cat-predicate>s.

  First, @<items> is evaluated, to yield a list.  The @<item-var> is bound,
  an empty list is created for each @|(@<cat-var> @<cat-predicate>)| pair,
  and an iteration is begun.  For each item in the list in turn is assigned
  to @<item-var>; then, the bindings given by the @|:bind| keyword are
  performed, as if by @|let*|; and the @<cat-predicate>s are evaluated in the
  resulting environment, one by one, until one of them returns non-nil.  When
  this happens, the item is added to the corresponding list.  If no predicate
  matches the item, an error is signalled.

  Once this iteration is complete, each @<cat-var> is bound to its
  corresponding completed list, and the body @<form>s are evaluated in the
  resulting environment (which does not include @<item-var>), as an implicit
  @|progn|, and the macro yields the values of the final @<form>.
\end{describe}

\begin{describe}{fun}{partial-order-minima @<items> @<order> @> @<list>}
  Return a list of minimal items from the list @<items> according to a
  non-strict partial order defined by the function @<order>: @|(funcall
  @<order> $x$ $y$)| should return non-nil if and only if $x \preceq y$ in
  the partial order.
\end{describe}

\begin{describe}{fun}{cross-product \&rest @<pieces>}
  Return the cross product of the @<pieces>.

  Each arguments may be a list, or a (non-nil) atom, which is equivalent to a
  singleton list containing just that atom.  Return a list of all possible
  lists which can be constructed by taking one item from each argument list
  in turn, in an arbitrary order.
\end{describe}

\begin{describe}{fun}
    {find-duplicates @<report> @<sequence> \&key :key :test}
  Call @<report> on each pair of duplicate items in a @<sequence>.
  Duplicates are determined according to the @<key> (by default @|identity|)
  and @<test> (by default @|eql|) functions, in the usual way: two items $x$
  and $y$ are considered equal if and only if @|(funcall @<test> (funcall
  @<key> $x$) (funcall @<key> $y$))| returns non-nil.

  The @<report> function is called as @|(funcall @<report> @<duplicate>
  @<previous>)|.  Duplicates are reported in order; the @<previous> item is
  always the first matching item in the sequence.

  This function will work for arbitrary @<test> functions, but it will run
  much more efficiently if @<test> is @|eq|, @|eql|, @|equal|, or @|equalp|,
  because it can use hash-tables.  (The generic implementation for lists is
  especially inefficient.)
\end{describe}


\subsection{Position tracking}

The following functions are used to maintain file positions: see
\xref{sec:parsing.floc}.  Columns are counted starting from zero at the far
left.  (No particular origin is needed for line numbers.)  Newlines, vertical
tabs, and form-feeds all move to the start of the next line; horizontal tabs
move to the next multiple of eight columns; other characters simply advance
to the next column.

\begin{describe}{fun}
    {update-position @<character> @<line> @<column>
      @> @<new-line> @<new-column>}
  Assume that we found @<character> at a particular @<line> and @<column> in
  a file: return the @<new-line> and @<new-column> for the next character.
\end{describe}

\begin{describe}{fun}
    {backtrack-position @<character> @<line> @<column>
      @> @<old-line> @<old-column>}
  Assume that we are currently at a particular @<line> and @<column> in a
  file, and wish to \emph{unread} @<character>: return an @<old-line> and
  @<old-column> at which we might plausibly re-read the character, so that
  the next call to \descref{fun}{update-position} will return us to @<line>
  and @<column>.  (Specifically, the @<old-column> will likely be wrong if
  @<character> is a horizontal tab.  It is expected that this won't matter:
  the purpose of this function is to set things up so that the
  @|update-position| call that will accompany re-reading the character will
  return the correct values, rather than to use the @<old-line> and
  @<old-column> for any other purpose.)
\end{describe}


\subsection{Object printing}

\begin{describe}{mac}
    {maybe-print-unreadable-object
        (@<object> @<stream>
         @[[ :type @<type> @!
             :identity @<identity> @]])                         \\ \ind
      @<declaration>^*                                          \\
      @<form>^*}
  If @|*print-escape*| is nil, then simply evaluate the @<form>s as an
  implicit @|progn|; otherwise, print an `unreadable' object, as if by
  \begin{prog}
    (print-unreadable-object
        (@<object> @<stream>
         @[:type @<type>@]
         @[:identity @<identity>@])                             \\ \ind
      @<form>^*)
  \end{prog}
\end{describe}

\begin{describe}{fun}{print-ugly-stuff @<stream> @<func> @> @<value>^*}
  If @<stream> is a pretty-printing stream, then print a mandatory newline,
  and call @<func> on the underlying non-pretty-printing stream.  If
  @<stream> is not a pretty-printing stream, then simply call @<func> on
  @<stream> directly.

  The main purpose for this is to be able to access features of the
  underlying stream which a pretty-printing stream can't proxy.  Most
  notably, this is used by C fragment output, which takes advantage of an
  underlying \descref{cls}{position-aware-output-stream} to print @|\#line|
  directives, so that a C~compiler will blame the original fragment in the
  Sod module source rather than the generated C code.
\end{describe}


\subsection{Condition utilities}

The following definitions are useful when working with conditions.

\begin{describe}{cls}
    {simple-control-error (control-error simple-error)
        \&key :format-control :format-arguments}
  This is the obvious multiply-inherited subclass of @|control-error| whose
  print form is determined by a @<format-control> and a @<format-arguments>
  list.
\end{describe}

\begin{describe}{fun}
    {designated-condition
        \=@<default-type> @<datum> @<arguments>                 \\
        \>\&key :allow-pointless-arguments
      \nlret @<condition>}
  Creates and returns a condition object of @<default-type>, given a
  condition designator @<datum> and @<arguments>.

  The Common Lisp specification carefully explains how a `datum' and an
  argument list together form a `condition designator', and how such a pair
  are to be converted into a condition object with some default type, but
  there's no mechanism provided to simply do this task.  (Functions like
  @|error| and @|signal| implicitly, but have possibly-undesirable
  side-effects, and don't allow control over the default type.)

  \begin{itemize}

  \item If @<datum> is a condition object, then the designated condition is
    simply @<datum>.  In this case, if @<arguments> is not an empty list and
    @<allow-pointless-arguments> is nil (the default), an error is signalled;
    otherwise, the @<arguments> are ignored.

  \item If @<datum> is a symbol, then the designated condition is constructed
    by calling
    \begin{prog}
      (apply \#'make-condition @<datum> @<arguments>)
    \end{prog}

  \item If @<datum> is a string or function (i.e., a `format-control'), then
    the designated condition is constructed by calling
    \begin{prog}
      (make-condition \=@<default-type>                         \\
                      \>:format-control @<datum>                \\
                      \>:format-arguments @<arguments>)
    \end{prog}

  \item Otherwise the designator is malformed, and an error is signalled.
  \end{itemize}
\end{describe}

\begin{describe}{fun}
    {invoke-associated-restart @<restart> @<condition> \&rest @<arguments>}
  Invoke the active restart named @<restart>, associated with the given
  @<condition>, passing a list of @<arguments>.

  The function attempts to find and invoke a restart with the given name.  If
  @<condition> is non-nil, then it searches among restarts associated with
  that specific condition, and restarts associated with no condition; if
  @<condition> is nil, then it searches among all restarts.

  If a matching restart is found, it is invoked, passing the @<arguments>
  list.  Otherwise, an error (of class @|control-error|) is signalled.
\end{describe}

\begin{describe*}
    {\dhead{cls}{enclosing-condition (condition) \&key :condition}
     \dhead{gf}{enclosed-condition @<enclosing-condition> @> @<condition>}}
  An @|enclosing condition| is a condition which contains another condition
  within it.  Objects of type @|enclosing-condition| are used to add
  additional information to an existing condition, or to alter the type of a
  condition without losing information.

  When an @|enclosing-condition| is constructed, the @<condition> argument
  names the existing condition to be enclosed.  This enclosed condition can
  be retrieved by calling @|enclosed-condition|.
\end{describe*}

\begin{describe}{cls}{information (condition) \&key}
  A condition of class @|information| conveys information which might be of
  interest, but does not of itself indicate that anything is wrong.

  Within a compiler, @|information| conditions may be signalled in order to
  present the user with additional diagnostic information about a recently
  reported error.
\end{describe}

\begin{describe}{cls}
    {simple-information (simple-condition information)          \\ \ind
      \&key :format-control :format-arguments}
  This is the obvious multiply-inherited subclass of @|information|
  whose print-representation is determined by a @<format-control> and a
  @<format-arguments> list.
\end{describe}

\begin{describe*}
    {\dhead{fun}{info @<datum> \&rest @<arguments> @> @<flag>}
     \dhead{rst}{noted}
     \dhead{fun}{noted \&optional @<condition>}}
  The @|info| function establishes a restart named @|noted| and signals a
  condition of default type @|simple-information|, designated by the @<datum>
  and @<arguments>.  The @|info| function returns non-nil if and only if the
  associated @|noted| restart was invoked.

  The @|noted| restart accepts no arguments.

  The @|noted| function finds and invokes a @|noted| restart: if @<condition>
  is non-nil, then only the restart associated with that condition (and those
  not associated with any condition) are considered; otherwise, all
  conditions are considered.
\end{describe*}

\begin{describe}{fun}
    {promiscuous-cerror @<continue-string> @<datum> \&rest @<arguments>}
  Establish a @|continue| restart and signal an error of default type
  @|simple-error|, designated by @<datum> and @<arguments>.  The restart's
  report format is determined by @<continue-string> and the @<arguments>.

  Some implementations of @|cerror| associate the @|continue| restart which
  they establish with the condition they signal.  This interferes with
  special effects -- specifically, enclosing the signalled condition and
  resignalling it.  The @|promiscuous-cerror| function carefully avoids
  associating its restart with the condition.
\end{describe}

\begin{describe}{fun}{cerror* @<datum> \&rest @<arguments>}
  A simplified version of \descref{fun}{promiscuous-cerror} which uses the
  hardcoded string @|Continue| for the restart.  This makes calling the
  function more similar to other condition-signalling functions, at the
  expense of some usability in environments which don't continue after
  continuable errors automatically.
\end{describe}


\subsection{Very miscellaneous utilities}

\begin{describe}{fun}
    {whitespace-char-p @<character> @> @<generalized-boolean>}
  Return non-nil if and only if @<character> is a whitespace character.

  A character is whitespace if @|(peek-char t @<stream>)| would skip it.
\end{describe}

\begin{describe}{fun}
    {frob-identifier @<string> \&key :swap-case :swap-hyphen
      @> @<frobbed-string>}
  Return a `frobbed' version of the identifier @<string>.  Two different
  transformations can be applied.

  \begin{itemize}

  \item If @<swap-case> is non-nil (the default), and the letters in
    @<string> are either all uppercase or all lowercase, then switch the case
    of all of the letters.

  \item If @<swap-hyphen> is non-nil (the default), and @<string> contains
    either hyphens @`--' or underscores @`_', but not both, then replace the
    hyphens by underscores or \emph{vice-versa}.

  \end{itemize}

  (These are the `obvious' transformations to convert a C identifier into a
  Lisp symbol.)

  Some examples:
  \begin{itemize}
  \item @|(frob-identifier "foo")| $\Longrightarrow$ @|"FOO"|
  \item @|(frob-identifier "FOO")| $\Longrightarrow$ @|"foo"|
  \item @|(frob-identifier "FooBar")| $\Longrightarrow$ @|"FooBar"|
  \item @|(frob-identifier "Foo-Bar")| $\Longrightarrow$ @|"Foo_Bar"|
  \item @|(frob-identifier "Foo_Bar")| $\Longrightarrow$ @|"Foo-Bar"|
  \item @|(frob-identifier "foo_bar")| $\Longrightarrow$ @|"FOO-BAR"|
  \item @|(frob-identifier "foo_bar" :swap-hyphen nil)| $\Longrightarrow$
    @|"FOO_BAR"|
  \item @|(frob-identifier "foo_bar" :swap-case nil)| $\Longrightarrow$
    @|"foo-bar"|
  \item @|(frob-identifier "foo_bar" :swap-case nil :swap-hyphen nil)|
    $\Longrightarrow$ @|"foo_bar"|
  \end{itemize}
\end{describe}

\begin{describe}{fun}
    {compose @<functions> @> @<function>}
  Return the left-to-right composition zero or more @<functions>.

  Let $f_1$, $f_2$, \ldots, $f_n$ be functions, and let $g = @|(compose $f_1$
  $f_2$ $\cdots$ $f_n$)|$ is their composition.  If $g$ is applied to
  arguments, the effect is as follows: first, $f_1$ is applied to the
  arguments, yielding some value; $f_2$ is applied to this value, yielding a
  second value; and so on, until finally the value yielded by $f_n$ is
  returned as the result of $g$.  Note that this is the reverse of the usual
  mathematician's convention, but the author finds this ordering
  significantly easier to work with:
  \[ g = f_n \circ \cdots \circ f_2 \circ f_1 \]

  If any of the input functions return multiple values then \emph{all} of the
  values are passed on to the next function in the list.  (If the last
  function returns multiple values then all of the values are returned from
  the composition.

  The result of composing no functions is a function which simply returns all
  of its arguments as values; essentially, $@|(compose)| \equiv
  @|\#'values|$.
\end{describe}

\begin{describe}{mac}{defvar-unbound @<name> @<documentation> @> @<name>}
  Define a variable called @<name>, with a @<documentation> string.

  The Common Lisp @|defvar| macro accepts both an initial value and a
  doc-string as optional arguments, in that order, with the result that it's
  not possible to define a variable and establish a documentation string for
  it without also giving it an initial value.  The @|defvar-unbound| macro,
  on the other hand, never changes the symbol's variable-value.
\end{describe}

\begin{describe}{mac}
    {dosequence (@<var> @<sequence>
                 @[[ :start @<start> @! :end @<end> @!
                     :indexvar @<index-var> @]])                \\ \ind
      @<declaration>^*                                          \\
      @{ @<tag> @! @<statement> @}^*}
  Iterate over a @<sequence>.  Common Lisp has a rich collection of iteration
  primitives, and a rich collection of functions for working with sequences,
  but no macro for iterating over the items of a sequence.

  First, the @<sequence> is evaluated.  If @<start> and/or @<end> are
  provided, they are also evaluated (in that order), which should produce
  integers; @<end> may be also be nil.  If not provided, or nil (in the case
  of @<end>), @<start> and @<end> default respectively to zero and the length
  of the @<sequence>.  For each item in the sequence between the @<start> and
  @<end> positions (i.e., each item in @|(subseq @<sequence> @<start>
  @<end>)|, in order, the body is evaluated as an implicit @|tagbody|, with
  @<var> bound to the item and, if provided, @<index-var> bound to the item's
  index.  It is not specified whether the @<var> and @<index-var> are
  let-bound or mutated in each iteration.

  Unlike other Common Lisp @|do|\dots\ forms, there is no `result' form.
\end{describe}

\begin{describe}{mac}
    {define-access-wrapper @<from> @<to>
                           @[[ :read-only @<read-only-flag> @]]}
  Define @<from> as a function of one argument, so that @|(@<from> @<thing>)|
  is equivalent to @|(@<to> @<thing>)|.  If @<read-only-flag> is nil (the
  default), then also define @|(setf @<from>)| so that @|(setf (@<from>
  @<thing>) @<value>)| is equivalent to @|(setf (@<to> @<thing>) @<value>)|.

  In a @|defstruct| form, the accessor function names are constructed based
  on the structure name and slot names.  The structure name and accessor
  names are part of the exported interface, but the slot names ideally
  shouldn't be.  This causes a problem when the slot name which will lead to
  the right accessor is already an external symbol in some package.  You can
  solve this problem by choosing an internal name for the symbol, and then
  using this macro to define an accessor function with the name that you
  want, in terms of the accessor that @|defstruct| made.
\end{describe}

\begin{describe}{fun}
    {distinguished-point-shortest-paths @<root> @<neighbours-func>
      @> @<list>}
  Calculate the shortest path from the @<root> to each node reachable from it
  in a directed graph.  The nodes of the graph can be any kind of object;
  they will be compared using @|eql|.

  The @<neighbours-func> should be a function which, given a node~$v$ as its
  only argument, returns a list of cons cells @|($v'$ . $c'$)|, one for each
  node~$v'$ adjacent to $v$, indicating the cost $c'$ of traversing the arc
  from $v$ to $v'$.

  The return value is a list of cons cells @|($c$ . $p$)|, where $p$ is list
  of nodes, in reverse order, along a path from the @<root> to some other
  node, and $c$ is the total cost of traversing this path.  (Therefore @|(car
  $p$)| is the destination node, and @|(car (last $p$))| is always the
  @<root> itself.)

  The function runs in $O(n^2)$ time, where $n$ is the number of nodes
  reachable from the @<root>.  Currently, it uses an algorithm due to Edsger
  Dijkstra.
\end{describe}


\subsection{Other exported symbols}

\begin{describe}{sym}{int}
  The symbol @|int| is exported by the @|sod-utilities| package, without
  giving it any particular meaning.  This is done because it's given
  non-conflicting meanings by two different packages, and it's more
  convenient for user code not to have to deal with an unnecessary symbol
  conflict.  Specifically, the @|sod| package wants to define it as a C type
  specifier, see \descref{cls}{simple-c-type}; and @|optparse| wants to
  define it as an option handler, see \descref{opt}{int}.
\end{describe}

%%%--------------------------------------------------------------------------
\section{Option parser} \label{sec:misc.optparse}

Most of these symbols are defined in the @|optparse| package.

\begin{describe}{var}{*program-name*}
\end{describe}

\begin{describe}{var}{*command-line*}
\end{describe}

\begin{describe}{fun}{set-command-line-arguments}
\end{describe}

\begin{describe}{fun}{moan @<format-string> \&rest @<format-args>}
\end{describe}

\begin{describe}{fun}{die @<format-string> \&rest @<format-args>}
\end{describe}

\begin{describe}{var}{*options*}
\end{describe}

\begin{describe}{cls}{option}
\end{describe}

\begin{describe}{fun}{optionp @<object> @> @<generalized-boolean>}
\end{describe}

\begin{describe}{fun}
    {make-option \=@<long-name> @<short-name>                 \+\\
                   \&optional @<arg-name>                       \\
                   \&key :tag :negated-tag
                         :arg-optional-p :documentation       \-
      \nlret @<option>}
\end{describe}

\begin{describe*}
    {\dhead{fun}{opt-short-name @<option> @> @<character-or-null>}
     \dhead{fun}{setf (opt-short-name @<option>) @<character-or-null>}
     \dhead{fun}{opt-long-name @<option> @> @<string-or-null>}
     \dhead{fun}{setf (opt-long-name @<option>) @<string-or-null>}
     \dhead{fun}{opt-tag @<option> @> @<tag>}
     \dhead{fun}{setf (opt-tag @<option>) @<tag>}
     \dhead{fun}{opt-negated-tag @<option> @> @<tag>}
     \dhead{fun}{setf (opt-negated-tag @<option>) @<tag>}
     \dhead{fun}{opt-arg-name @<option> @> @<string-or-null>}
     \dhead{fun}{setf (opt-arg-name @<option>) @<string-or-null>}
     \dhead{fun}{opt-arg-optional-p @<option> @> @<generalized-boolean>}
     \dhead{fun}{setf (opt-arg-optional-p @<option>) @<generalized-boolean>}
     \dhead{fun}{opt-documentation @<option> @> @<string-or-null>}
     \dhead{fun}{setf (opt-documentation @<option>) @<string-or-null>}}
\end{describe*}

\begin{describe}{cls}{option-parser}
\end{describe}

\begin{describe}{fun}{option-parser-p @<object> @> @<generalized-boolean>}
\end{describe}

\begin{describe}{fun}
    {make-option-parser \&key \=:args :options :non-option :numericp \+ \\
                              :negated-numeric-p long-only-p \-
      \nlret @<option-parser>}
\end{describe}

\begin{describe*}
    {\dhead{fun}{op-options @<option-parser> @> @<list>}
     \dhead{fun}{setf (op-options @<option-parser>) @<list>}
     \dhead{fun}{op-non-option @<option-parser> @> @<action>}
     \dhead{fun}{setf (op-non-option @<option-parser>) @<action>}
     \dhead{fun}{op-long-only-p @<option-parser> @> @<generalized-boolean>}
     \dhead{fun}{setf (op-long-only-p @<option-parser>) @<generalized-boolean>}
     \dhead{fun}{op-numeric-p @<option-parser> @> @<generalized-boolean>}
     \dhead{fun}{setf (op-numeric-p @<option-parser>) @<generalized-boolean>}
     \dhead{fun}{op-negated-numeric-p @<option-parser> @<generalized-boolean>}
     \dhead{fun}{setf (op-negated-numeric-p @<option-parser>) @<generalized-boolean>}
     \dhead{fun}{op-negated-p @<option-parser> @> @<generalized-boolean>}
     \dhead{fun}{setf (op-negated-p @<option-parser>) @<generalized-boolean>}}
\end{describe*}

\begin{describe}{cls}
    {option-parse-error (error simple-condition)
      \&key :format-control :format-arguments}
\end{describe}

\begin{describe}{fun}{option-parse-error @<msg> \&optional @<args>}
\end{describe}

\begin{describe}{fun}{option-parse-remainder @<option-parser>}
\end{describe}

\begin{describe}{fun}{option-parse-return @<tag> \&optional @<argument>}
\end{describe}

\begin{describe}{fun}{option-parse-next @<option-parser>}
\end{describe}

\begin{describe}{mac}{option-parse-try @<form>^*}
\end{describe}

\begin{describe}{mac}{with-unix-error-reporting () @<form>^*}
\end{describe}

\begin{describe}{mac}
    {defopthandler @<name> (@<var> @[@<arg>@]) @<lambda-list> \\ \ind
      @[[ @<declaration>^* @! @<doc-string> @]] \\
      @<form>^*}
\end{describe}

\begin{describe*}
    {\dhead{sym}{opthandler}
     \dhead{meth}{symbol,(eql 'opthandler)}
                 {documentation (@<symbol> symbol)
                                (@<doc-type> (eql 'opthandler))}
     \dhead{meth}{symbol,(eql 'opthandler)}
                 {setf \=(documentation (@<symbol> symbol)
                                        (@<doc-type> (eql 'opthandler))) \\
                       \>@<string>}}
\end{describe*}

\begin{describe}{fun}
    {invoke-option-handler @<handler> @<locative> @<arg> @<arguments>}
\end{describe}

\begin{describe}{opt}{set \&optional @<value>}
\end{describe}

\begin{describe}{opt}{clear \&optional @<value>}
\end{describe}

\begin{describe}{opt}{inc \&optional @<maximum> @<step>}
\end{describe}

\begin{describe}{opt}{dec \&optional @<minimum> @<step>}
\end{describe}

\begin{describe}{opt}{read}
\end{describe}

\begin{describe}{opt}{int \&key :radix :min :max}
\end{describe}

\begin{describe}{opt}{string}
\end{describe}

\begin{describe}{opt}{keyword \&optional @<valid>}
\end{describe}

\begin{describe}{opt}{list \&optional @<handler> \&rest @<handler-args>}
\end{describe}

\begin{describe}{mac}
    {defoptmacro @<name> @<lambda-list> \\ \ind
      @[[ @<declaration>^* @! @<doc-string> @]] \\
      @<form>^*}
\end{describe}

\begin{describe*}
    {\dhead{sym}{optmacro}
     \dhead{meth}{symbol,(eql 'optmacro)}
                 {documentation (@<symbol> symbol)
                                (@<doc-type> (eql 'optmacro))}
     \dhead{meth}{symbol,(eql 'optmacro)}
                 {setf \=(documentation (@<symbol> symbol)
                                        (@<doc-type> (eql 'optmacro))) \\
                       \>@<string>}}
\end{describe*}

\begin{describe}{fun}{parse-option-form @<form>}
\end{describe}

\begin{describe}{mac}
    {options @{ \=@<string> @! \+ \\
                  @<option-macro> @! (@<option-macro> @<macro-arg>^*) @! \\
                  (@[[ \=@<character> @! (:short-name @<character>) @! \+ \\
                         @<string>^* @! @<symbol> @! @<rational> @!
                         (:long-name @<string>) @! \\
                         (@<string> @<format-arg>^+) @!
                         (:doc @<string> @<format-arg>^*) @! \\
                         (:arg @<arg-name>) @! (:opt-arg @<arg-name>) @! \\
                         @<keyword> @! (:tag @<tag>) @!
                                       (:negated-tag @<tag>) @! \\
                         @{ (@<handler> @<var> @<handler-arg>^*) @}^*
                   @]]) @}^*}
\end{describe}

\begin{describe}{fun}
    {simple-usage @<option-list> \&optional @<mandatory-args> @> @<list>}
\end{describe}

\begin{describe}{fun}{show-usage @<prog> @<usage> \&optional @<stream>}
\end{describe}

\begin{describe}{fun}
    {show-help @<prog> @<usage> @<option-list> \&optional @<stream>}
\end{describe}

\begin{describe}{fun}{sanity-check-option-list @<option-list>}
\end{describe}

\begin{describe*}
    {\dhead{var}{*help*}
     \dhead{var}{*version*}
     \dhead{var}{*usage*}}
\end{describe*}

\begin{describe}{fun}{do-usage \&optional @<stream>}
\end{describe}

\begin{describe}{fun}{die-usage}
\end{describe}

\begin{describe}{optmac}
    {help-options \&key :short-help :short-version :short-usage}
\end{describe}

\begin{describe}{fun}
    {define-program \&key \=:program-name \+ \\
                            :help :version :usage :full-usage \\
                            :options}
\end{describe}

\begin{describe}{mac}
    {do-options (@[[ :parser @<option-parser> @]]) \\ \ind
      @{ (@{ @<case> @! (@<case>^*)@} (@[@[@<opt-var>@] @<arg-var>@])
          @<form>^*) @}^*}
\end{describe}

\begin{describe}{fun}{sod-frontend:augment-options @<options-list>}
\end{describe}

%%%--------------------------------------------------------------------------
\section{Property sets} \label{sec:misc.pset}

\begin{describe}{fun}{property-key @<name> @> @<keyword>}
\end{describe}

\begin{describe}{gf}{decode-property @<raw-value> @> @<type> @<value>}
\end{describe}

\begin{describe}{cls}{property}
\end{describe}

\begin{describe}{fun}{propertyp @<object> @> @<generalized-boolean>}
\end{describe}

\begin{describe}{fun}
    {make-property @<name> @<raw-value> \&key :type :location :seenp}
\end{describe}

\begin{describe*}
    {\dhead{fun}{p-name @<property> @> @<name>}
     \dhead{meth}{property}{file-location (@<property> property) @> @<floc>}
     \dhead{fun}{p-value @<property> @> @<value>}
     \dhead{fun}{p-type @<property> @> @<type>}
     \dhead{fun}{p-key @<property> @> @<symbol>}
     \dhead{fun}{p-seenp @<property> @> @<boolean>}
     \dhead{fun}{setf (p-seenp @<property>) @<boolean>}}
\end{describe*}

\begin{describe}{gf}
    {coerce-property-value @<value> @<type> @<wanted> @> @<coerced-value>}
\end{describe}

\begin{describe}{cls}{pset}
\end{describe}

\begin{describe}{fun}{psetp @<object> @> @<generalized-boolean>}
\end{describe}

\begin{describe}{fun}{make-pset @> @<pset>}
\end{describe}

\begin{describe}{fun}{pset-get @<pset> @<key> @> @<property-or-nil>}
\end{describe}

\begin{describe}{fun}{pset-store @<pset> @<property> @> @<property>}
\end{describe}

\begin{describe}{fun}{pset-map @<func> @<pset>}
\end{describe}

\begin{describe}{mac}
    {with-pset-iterator (@<iter> @<pset>) @<declaration>^* @<form>^*}
\end{describe}

\begin{describe}{fun}
    {store-property @<pset> @<name> @<value> \&key :type :location
      @> @<property>}
\end{describe}

\begin{describe}{fun}
    {get-property @<pset> @<name> @<type> \&optional @<default>
      @> @<value> @<floc-or-nil>}
\end{describe}

\begin{describe}{fun}
    {add-property @<pset> @<name> @<value> \&key :type :location
      @> @<property>}
\end{describe}

\begin{describe}{fun}{make-property-set \&rest @<plist> @> @<pset>}
\end{describe}

\begin{describe}{gf}{property-set @<thing> @> @<pset>}
\end{describe}

\begin{describe}{fun}{check-unused-properties @<pset>}
\end{describe}

\begin{describe}{mac}
    {default-slot-from-property
        (@<instance> @<slot> @[@<slot-names>@]) \\ \ind\ind
        (@<pset> @<property> @<type> @[@<prop-var> @<convert-form>^*@]) \- \\
      @<declaration>^* \\
      @<default-form>^*}
\end{describe}

\begin{describe}{fun}
    {parse-property @<scanner> @<pset>
      @> @<result> @<success-flag> @<consumed-flag>}
\end{describe}

\begin{describe}{fun}
    {parse-property-set @<scanner>
      @> @<result> @<success-flag> @<consumed-flag>}
\end{describe}

%%%--------------------------------------------------------------------------
\section{Miscellaneous translator features} \label{sec:misc.misc}

\begin{describe}{var}{*sod-version*}
\end{describe}

\begin{describe}{var}{*debugout-pathname*}
\end{describe}

\begin{describe}{fun}
    {test-module @<path> \&key :reason :clear :backtrace @> @<status>}
\end{describe}

\begin{describe}{fun}
    {test-parse-c-type @<string>
      @> t @<c-type> @<kernel> @<string> @! nil @<indicator>}
\end{describe}

\begin{describe}{fun}
    {test-parse-pset @<string>
      @> t @<pset> @! nil @<indicator>}
\end{describe}

\begin{describe}{mac}
    {test-parser (@<scanner> \&key :backtrace) @<parser> @<input>
      @> @<result> @<status> @<remainder>}
\end{describe}

\begin{describe}{fun}{exercise}
\end{describe}

\begin{describe}{fun}{sod-frontend:main}
\end{describe}

%%%----- That's all, folks --------------------------------------------------

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