Document cl-print.el in cl.texi.

* doc/misc/cl.texi: (Printing): New chapter which documents
cl-print.el.

* NEWS (cl-print): Add "+++" markings to all the subitems,
which have now been documented.

2 files changed, 164 insertions, 0 deletions

diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index 5de33350f4f..e5a29cbcffb 100644
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -55,6 +55,7 @@ modify this GNU manual.''
 
 @menu
 * Overview::             Basics, usage, organization, naming conventions.
+* Printing::             Human friendly printing with @code{cl-prin1}.
 * Program Structure::    Arglists, @code{cl-eval-when}.
 * Predicates::           Type predicates and equality predicates.
 * Control Structure::    Assignment, conditionals, blocks, looping.
@@ -258,6 +259,160 @@ and @code{:key} is not used.
 @noindent
 [3] Only for one sequence argument or two list arguments.
 
+@node Printing
+@chapter Printing
+
+@noindent
+This chapter describes some enhancements to Emacs Lisp's
+@dfn{printing}, the action of representing Lisp objects in text form.
+The functions documented here are intended to produce output more for
+human readers than the standard printing functions such as
+@code{prin1} and @code{princ} (@pxref{Output Functions,,,elisp,GNU
+Emacs Lisp Reference Manual}).
+
+Several of these functions have a parameter @var{stream}; this
+specifies what to do with the characters printing produces.  For
+example, it might be a buffer, a marker, @code{nil} (meaning use
+standard output), or @code{t} (use the echo area).  @xref{Output
+Streams,,,elisp,GNU Emacs Lisp Reference Manual}, for a full
+description.
+
+@defvar cl-print-readably
+When this variable is non-@code{nil}, @code{cl-prin1} and other
+functions described here try to produce output which can later be read
+by the Lisp reader (@pxref{Input Functions,,,elisp,GNU Emacs Lisp
+Reference Manual}).
+@end defvar
+
+@defvar cl-print-compiled
+This variable controls how to print byte-compiled functions.  Valid
+values are:
+@table @code
+@item nil
+The default: Just an internal hex identifier is printed.
+@item static
+The internal hex identifier together with the function's constant
+vector are printed.
+@item disassemble
+The byte code gets disassembled.
+@item raw
+The raw form of the function is printed by @code{prin1}.
+@end table
+
+Sometimes, a button is set on the output to allow you to disassemble
+the function.  See @code{cl-print-compile-button}.
+@end defvar
+
+@defvar cl-print-compile-button
+When this variable is non-@code{nil} and a byte-compiled function has
+been printed to a buffer, you can click with the mouse or type
+@key{RET} on that output to disassemble the code.  This doesn't apply
+when @code{cl-print-compiled} is set to @code{disassemble}.
+@end defvar
+
+@defvar cl-print-string-length
+The maximum length of a string to print before abbreviating it.  A
+value of @code{nil}, the default, means no limit.
+
+When the CL printing functions abbreviate a string, they print the
+first @code{cl-print-string-length} characters of the string, followed
+by ``@enddots{}''.  When the printing is to a buffer, you can click
+with the mouse or type @key{RET} on this ellipsis to expand the
+string.
+
+This variable has effect only in the @code{cl-prin*} functions, not in
+primitives such as @code{prin1}.
+@end defvar
+
+@defun cl-prin1 object &option stream
+@code{cl-print1} prints @var{object} on @var{stream} (see above)
+according to its type and the settings described above.  The variables
+@code{print-length} and @code{print-level} and the other standard
+Emacs settings also affect the printing (@pxref{Output
+Variables,,,elisp,GNU Emacs Lisp Reference Manual}).
+@end defun
+
+@defun cl-prin1-to-string object
+This function is like @code{cl-prin1}, except the output characters
+are returned as a string from this function rather than being passed
+to a stream.
+@end defun
+
+@defun cl-print-to-string-with-limit print-function value limit
+This function returns a string containing a printed representation of
+@var{value}.  It attempts to get the length of the returned string
+under @var{limit} characters with successively more restrictive
+settings of @code{print-level}, @code{print-length}, and
+@code{cl-print-string-length}.  It uses @var{print-function} to print,
+a function which should take the arguments @var{value} and a stream
+(see above), and which should respect @code{print-length},
+@code{print-level}, and @code{cl-print-string-length}.  @var{limit}
+may be @code{nil} or zero, in which case @var{print-function} will be
+called with these settings bound to @code{nil}; it can also be
+@code{t}, in which case @var{print-function} will be called with their
+current values.
+
+Use this function with @code{cl-prin1} to print an object, possibly
+abbreviating it with one or more ellipses to fit within the size
+limit.
+@end defun
+
+@defun cl-print-object object stream
+This function prints @var{object} on @var{stream} (see above).  It is
+actually a @code{cl-defgeneric} (@pxref{Generic Functions,,,elisp,GNU
+Emacs Lisp Reference Manual}), which is defined for several types of
+@var{object}.  Normally, you just call @code{cl-prin1} to print an
+@var{object} rather than calling this function directly.
+
+You can write @code{cl-print-object} @code{cl-defmethod}s for other
+types of @var{object}, thus extending @code{cl-prin1}.  If such a
+method uses ellipses, you should also write a
+@code{cl-print-object-contents} method for the same type.  For
+examples of these methods, see @file{emacs-lisp/cl-print.el} in the
+Emacs source directory.
+@end defun
+
+@defun cl-print-object-contents object start stream
+This function replaces an ellipsis in @var{stream} beginning at
+@var{start} with the text from the partially printed @var{object} it
+represents.  It is also a @code{cl-defgeneric} defined for several
+types of @var{object}.  @var{stream} is a buffer containing the text
+with the ellipsis.  @var{start} specifies the starting position of the
+ellipsis in a manner dependent on the type; it will have been obtained
+from a text property on the ellipsis, having been put there by
+@code{cl-print-insert-ellipsis}.
+@end defun
+
+@defun cl-print-insert-ellipsis object start stream
+This function prints an ellipsis (``@dots{}'') to @var{stream} (see
+above).  When @var{stream} is a buffer, the ellipsis will be given the
+@code{cl-print-ellipsis} text property.  The value of the text
+property will contain state (including @var{start}) in order to print
+the elided part of @var{object} later.  @var{start} should be nil if
+the whole @var{object} is being elided, otherwise it should be an
+index or other pointer into the internals of @var{object} which can be
+passed to `cl-print-object-contents' at a later time.
+@end defun
+
+@defvar cl-print-expand-ellipsis-function
+This variable holds a function which expands an ellipsis in the
+current buffer.  The function takes four arguments: @var{begin} and
+@var{end}, which are the bounds of the ellipsis; @var{value}, which is
+the value of the @code{cl-print-ellipsis} text property on the
+ellipsis (typically set earlier by @code{cl-prin1}); and
+@var{line-length}, the desired maximum length of the output.  Its
+return value is the buffer position after the expanded text.
+@end defvar
+
+@deffn Command cl-print-expand-ellipsis &optional button
+This command expands the ellipsis at point.  Non-interactively, if
+@var{button} is non-@code{nil}, it should be either a buffer position
+or a button made by @code{cl-print-insert-ellipsis}
+(@pxref{Buttons,,,elisp,GNU Emacs Lisp Reference Manual}), which
+indicates the position of the ellipsis.  The return value is the
+buffer position after the expanded text.
+@end deffn
+
 @node Program Structure
 @chapter Program Structure
 
diff --git a/etc/NEWS b/etc/NEWS
index 6637a5c87e2..8b2bcaaf01d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -150,22 +150,31 @@ executable, if it exists.  This should remove the need to change its
 value when installing GNU coreutils using something like ports or
 Homebrew.
 
++++
 ** cl-print
 
++++
 *** You can expand the "..." truncation everywhere.
 The code that allowed "..." to be expanded in the "*Backtrace*" buffer
 should now work anywhere the data is generated by 'cl-print'.
 
++++
 *** The 'backtrace-ellipsis' button is replaced by 'cl-print-ellipsis'.
 
++++
 *** hash-tables' contents can be expanded via the ellipsis.
 
++++
 *** Modes can control the expansion via 'cl-print-expand-ellipsis-function'.
 
++++
 *** There is a new setting 'raw' for 'cl-print-compiled' which causes
 byte-compiled functions to be printed in full by 'prin1'.  A button on
 this output can be activated to disassemble the function.
 
++++
+*** There is a new chapter in the CL manual documenting cl-print.el.
+
 ** Modeline elements can now be right-aligned.
 Anything following the symbol 'mode-line-format-right-align' in
 'mode-line-format' will be right-aligned.  Exactly where it is