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Module Formatmodule Format:
Pretty printing.
This module implements a pretty-printing facility to format text within ``pretty-printing boxes''. The pretty-printer breaks lines at specified break hints, and indents lines according to the box structure. Warning: the material output by the following functions is delayed in the pretty-printer queue in order to compute the proper line breaking. Hence, you should not mix calls to the printing functions of the basic I/O system with calls to the functions of this module: this could result in some strange output seemingly unrelated with the evaluation order of printing commands.
You may consider this module as providing an extension to the
You may also use the explicit box management and printing functions
provided by this module. This style is more basic but more verbose
than the
For instance, the sequence
Rule of thumb for casual users of this library:
open_ functions below must be closed using close_box
for proper formatting. Otherwise, some of the material printed in the
boxes may not be output, or may be formatted incorrectly.
In case of interactive use, the system closes all opened boxes and
flushes all pending text (as with the
val open_box : open_box d opens a new pretty-printing box
with offset d .
This box is the general purpose pretty-printing box.
Material in this box is displayed ``horizontal or vertical'':
break hints inside the box may lead to a new line, if there
is no more room on the line to print the remainder of the box,
or if a new line may lead to a new indentation
(demonstrating the indentation of the box).
When a new line is printed in the box, d is added to the
current indentation.val close_box :
Closes the most recently opened pretty-printing box.
val print_string : print_string str prints str in the current box.val print_as : print_as len str prints str in the
current box. The pretty-printer formats str as if
it were of length len .val print_int :
Prints an integer in the current box.
val print_float :
Prints a floating point number in the current box.
val print_char :
Prints a character in the current box.
val print_bool :
Prints a boolean in the current box.
val print_space : print_space () is used to separate items (typically to print
a space between two words).
It indicates that the line may be split at this
point. It either prints one space or splits the line.
It is equivalent to print_break 1 0 .val print_cut : print_cut () is used to mark a good break position.
It indicates that the line may be split at this
point. It either prints nothing or splits the line.
This allows line splitting at the current
point, without printing spaces or adding indentation.
It is equivalent to print_break 0 0 .val print_break :
Inserts a break hint in a pretty-printing box.
print_break nspaces offset indicates that the line may
be split (a newline character is printed) at this point,
if the contents of the current box does not fit on the
current line.
If the line is split at that point, offset is added to
the current indentation. If the line is not split,
nspaces spaces are printed.val print_flush :
Flushes the pretty printer: all opened boxes are closed,
and all pending text is displayed.
val print_newline :
Equivalent to
print_flush followed by a new line.val force_newline :
Forces a newline in the current box. Not the normal way of
pretty-printing, you should prefer break hints.
val print_if_newline :
Executes the next formatting command if the preceding line
has just been split. Otherwise, ignore the next formatting
command.
val set_margin : set_margin d sets the value of the right margin
to d (in characters): this value is used to detect line
overflows that leads to split lines.
Nothing happens if d is smaller than 2 or
bigger than 999999999.val get_margin :
Returns the position of the right margin.
val set_max_indent : set_max_indent d sets the value of the maximum
indentation limit to d (in characters):
once this limit is reached, boxes are rejected to the left,
if they do not fit on the current line.
Nothing happens if d is smaller than 2 or
bigger than 999999999.val get_max_indent :
Return the value of the maximum indentation limit (in characters).
val set_max_boxes : set_max_boxes max sets the maximum number
of boxes simultaneously opened.
Material inside boxes nested deeper is printed as an
ellipsis (more precisely as the text returned by
get_ellipsis_text () ).
Nothing happens if max is not greater than 1.val get_max_boxes :
Returns the maximum number of boxes allowed before ellipsis.
val over_max_boxes :
Tests if the maximum number of boxes allowed have already been opened.
val open_hbox : open_hbox () opens a new pretty-printing box.
This box is ``horizontal'': the line is not split in this box
(new lines may still occur inside boxes nested deeper).val open_vbox : open_vbox d opens a new pretty-printing box
with offset d .
This box is ``vertical'': every break hint inside this
box leads to a new line.
When a new line is printed in the box, d is added to the
current indentation.val open_hvbox : open_hvbox d opens a new pretty-printing box
with offset d .
This box is ``horizontal-vertical'': it behaves as an
``horizontal'' box if it fits on a single line,
otherwise it behaves as a ``vertical'' box.
When a new line is printed in the box, d is added to the
current indentation.val open_hovbox : open_hovbox d opens a new pretty-printing box
with offset d .
This box is ``horizontal or vertical'': break hints
inside this box may lead to a new line, if there is no more room
on the line to print the remainder of the box.
When a new line is printed in the box, d is added to the
current indentation.
val open_tbox :
Opens a tabulation box.
val close_tbox :
Closes the most recently opened tabulation box.
val print_tbreak :
Break hint in a tabulation box.
print_tbreak spaces offset moves the insertion point to
the next tabulation (spaces being added to this position).
Nothing occurs if insertion point is already on a
tabulation mark.
If there is no next tabulation on the line, then a newline
is printed and the insertion point moves to the first
tabulation of the box.
If a new line is printed, offset is added to the current
indentation.val set_tab :
Sets a tabulation mark at the current insertion point.
val print_tab : print_tab () is equivalent to print_tbreak (0,0) .
val set_ellipsis_text :
Set the text of the ellipsis printed when too many boxes
are opened (a single dot,
. , by default).val get_ellipsis_text :
Return the text of the ellipsis.
type tag =
Tags are used to decorate printed entities for user's defined purposes, e.g. setting font and giving size indications for a display device, or marking delimitations of semantics entities (e.g. HTML or TeX elements or terminal escape sequences). By default, those tags do not influence line breaking calculation: the tag ``markers'' are not considered as part of the printing material that drive line breaking (in other words, the length of those strings is considered as zero for line breaking).
Thus, tag handling is in some sense transparent to pretty-printing
and do not interfere with usual pretty-printing. Hence, a single
pretty printing routine can output both simple ``verbatim''
material or richer decorated output depending on the treatment of
tags. Default behavior of the pretty printer engine is to consider
tags as active, so that output is decorated. Otherwise, if
When a tag has been opened (or closed), it is both and successively ``printed'' and ``marked''. Printing a tag means calling a formatter specific function with the name of the tag as argument: that ``tag printing'' function can then print any regular material to the formatter (so that this material is enqueued as usual in the formatter queue for further line-breaking computation). Marking a tag means to output an arbitrary string (the ``tag marker''), directly into the output device of the formatter. Hence, the formatter specific ``tag marking'' function must return the tag marker string associated to its tag argument. Being flushed directly into the output device of the formatter, tag marker strings are not considered as part of the printing material that drive line breaking (in other words, the length of the strings corresponding to tag markers is considered as zero for line breaking). In addition, advanced users may take advantage of the specificity of tag markers to be precisely output when the pretty printer has already decided where to break the lines, and precisely when the queue is flushed into the output device.
In the spirit of HTML tags, the default tag marking functions
output tags enclosed in "<" and ">": hence, the opening marker of
tag Default tag printing functions just do nothing.
Tag marking and tag printing functions are user definable and can
be set by calling val open_tag : open_tag t opens the tag named t ; the print_open_tag
function of the formatter is called with t as argument;
the tag marker mark_open_tag t will be flushed into the output
device of the formatter.val close_tag : close_tag () closes the most recently opened tag t .
In addition, the print_close_tag function of the formatter is called
with t as argument. The marker mark_close_tag t will be flushed
into the output device of the formatter.val set_tags : set_tags b turns on or off the treatment of tags (default is on).val set_print_tags : val set_mark_tags : set_print_tags b turns on or off the printing of tags, while
set_mark_tags b turns on or off the output of tag markers.val get_print_tags : val get_mark_tags :
Return the current status of tag printing and marking.
val set_formatter_out_channel :
Redirect the pretty-printer output to the given channel.
val set_formatter_output_functions : set_formatter_output_functions out flush redirects the
pretty-printer output to the functions out and flush .
The val get_formatter_output_functions :
Return the current output functions of the pretty-printer.
type formatter_tag_functions = {
The tag handling functions specific to a formatter:
mark versions are the ``tag marking'' functions that associate a string
marker to a tag in order for the pretty-printing engine to flush
those markers as 0 length tokens in the output device of the formatter.
print versions are the ``tag printing'' functions that can perform
regular printing when a tag is closed or opened.val set_formatter_tag_functions : set_formatter_tag_functions tag_funs changes the meaning of
opening and closing tags to use the functions in tag_funs .
When opening a tag name
The val get_formatter_tag_functions :
Return the current tag functions of the pretty-printer.
val set_all_formatter_output_functions : set_all_formatter_output_functions out flush outnewline outspace
redirects the pretty-printer output to the functions out and
flush as described in set_formatter_output_functions . In
addition, the pretty-printer function that outputs a newline is set
to the function outnewline and the function that outputs
indentation spaces is set to the function outspace .
This way, you can change the meaning of indentation (which can be
something else than just printing space characters) and the
meaning of new lines opening (which can be connected to any other
action needed by the application at hand). The two functions
val get_all_formatter_output_functions :
Return the current output functions of the pretty-printer,
including line breaking and indentation functions.
type formatter
Abstract data type corresponding to a pretty-printer (also called a
formatter) and all its machinery.
Defining new pretty-printers permits the output of
material in parallel on several channels.
Parameters of a pretty-printer are local to this pretty-printer:
margin, maximum indentation limit, maximum number of boxes
simultaneously opened, ellipsis, and so on, are specific to
each pretty-printer and may be fixed independently.
Given an output channel
oc , a new formatter writing to
that channel is obtained by calling formatter_of_out_channel oc .
Alternatively, the make_formatter function allocates a new
formatter with explicit output and flushing functions
(convenient to output material to strings for instance).val formatter_of_out_channel : formatter_of_out_channel oc returns a new formatter that
writes to the corresponding channel oc .val std_formatter :
The standard formatter used by the formatting functions
above. It is defined as
formatter_of_out_channel stdout .val err_formatter :
A formatter to use with formatting functions below for
output to standard error. It is defined as
formatter_of_out_channel stderr .val formatter_of_buffer : formatter_of_buffer b returns a new formatter writing to
buffer b . As usual, the formatter has to be flushed at
the end of pretty printing, using pp_print_flush or
pp_print_newline , to display all the pending material.val stdbuf :
The string buffer in which
str_formatter writes.val str_formatter :
A formatter to use with formatting functions below for
output to the
stdbuf string buffer.
str_formatter is defined as formatter_of_buffer stdbuf .val flush_str_formatter :
Returns the material printed with
str_formatter , flushes
the formatter and resets the corresponding buffer.val make_formatter : make_formatter out flush returns a new formatter that
writes according to the output function out , and the flushing
function flush . Hence, a formatter to the out channel oc
is returned by make_formatter (output oc) (fun () -> flush oc) .
val pp_open_hbox : val pp_open_vbox : val pp_open_hvbox : val pp_open_hovbox : val pp_open_box : val pp_close_box : val pp_open_tag : val pp_close_tag : val pp_print_string : val pp_print_as : val pp_print_int : val pp_print_float : val pp_print_char : val pp_print_bool : val pp_print_break : val pp_print_cut : val pp_print_space : val pp_force_newline : val pp_print_flush : val pp_print_newline : val pp_print_if_newline : val pp_open_tbox : val pp_close_tbox : val pp_print_tbreak : val pp_set_tab : val pp_print_tab : val pp_set_tags : val pp_set_print_tags : val pp_set_mark_tags : val pp_get_print_tags : val pp_get_mark_tags : val pp_set_margin : val pp_get_margin : val pp_set_max_indent : val pp_get_max_indent : val pp_set_max_boxes : val pp_get_max_boxes : val pp_over_max_boxes : val pp_set_ellipsis_text : val pp_get_ellipsis_text : val pp_set_formatter_out_channel : val pp_set_formatter_output_functions : val pp_get_formatter_output_functions : val pp_set_all_formatter_output_functions : val pp_get_all_formatter_output_functions : val pp_set_formatter_tag_functions : val pp_get_formatter_tag_functions :
These functions are the basic ones: usual functions
operating on the standard formatter are defined via partial
evaluation of these primitives. For instance,
print_string is equal to pp_print_string std_formatter .
val fprintf : fprintf ff format arg1 ... argN formats the arguments
arg1 to argN according to the format string format ,
and outputs the resulting string on the formatter ff .
The format is a character string which contains three types of
objects: plain characters and conversion specifications as
specified in the printf module, and pretty-printing
indications.
The pretty-printing indication characters are introduced by
a @ character, and their meanings are:
printf "@[%s@ %d@]" "x =" 1 is equivalent to
open_box (); print_string "x ="; print_space (); print_int 1; close_box () .
It prints x = 1 within a pretty-printing box.val printf :
Same as
fprintf above, but output on std_formatter .val eprintf :
Same as
fprintf above, but output on err_formatter .val sprintf :
Same as
printf above, but instead of printing on a formatter,
returns a string containing the result of formatting the arguments.
Note that the pretty-printer queue is flushed at the end of each
call to sprintf .
In case of multiple and related calls to val bprintf :
Same as
sprintf above, but instead of printing on a string,
writes into the given extensible buffer.
As for sprintf , the pretty-printer queue is flushed at the end of each
call to bprintf .
In case of multiple and related calls to val kprintf :
Same as
sprintf above, but instead of returning the string,
passes it to the first argument. |