NAME¶
Format - Pretty printing.
Module¶
Module Format
Documentation¶
Module
Format
:
sig end
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.
For a gentle introduction to the basics of pretty-printing using
Format ,
read
http://caml.inria.fr/resources/doc/guides/format.html.
You may consider this module as providing an extension to the
printf
facility to provide automatic line breaking. The addition of pretty-printing
annotations to your regular
printf formats gives you fancy indentation
and line breaks. Pretty-printing annotations are described below in the
documentation of the function
Format.fprintf .
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
fprintf
concise formats.
For instance, the sequence
open_box 0; print_string x = ; print_space ();
print_int 1; close_box (); print_newline () that prints
x = 1
within a pretty-printing box, can be abbreviated as
printf @[%s@ %i@]@. x =
1 , or even shorter
printf @[x =@ %i@]@. 1 .
Rule of thumb for casual users of this library:
-use simple boxes (as obtained by
open_box 0 );
-use simple break hints (as obtained by
print_cut () that outputs a
simple break hint, or by
print_space () that outputs a space indicating
a break hint);
-once a box is opened, display its material with basic printing functions (e. g.
print_int and
print_string );
-when the material for a box has been printed, call
close_box () to close
the box;
-at the end of your routine, flush the pretty-printer to display all the
remaining material, e.g. evaluate
print_newline () .
The behaviour of pretty-printing commands is unspecified if there is no opened
pretty-printing box. Each box opened via one of the
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
print_newline function) after each phrase.
Each phrase is therefore executed in the initial state of the pretty-printer.
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.
=== Boxes ===
val open_box :
int -> unit
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 :
unit -> unit
Closes the most recently opened pretty-printing box.
=== Formatting functions ===
val print_string :
string -> unit
print_string str prints
str in the current box.
val print_as :
int -> string -> unit
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 :
int -> unit
Prints an integer in the current box.
val print_float :
float -> unit
Prints a floating point number in the current box.
val print_char :
char -> unit
Prints a character in the current box.
val print_bool :
bool -> unit
Prints a boolean in the current box.
=== Break hints ===
val print_space :
unit -> unit
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 :
unit -> unit
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 :
int -> int -> unit
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 :
unit -> unit
Flushes the pretty printer: all opened boxes are closed, and all pending text is
displayed.
val print_newline :
unit -> unit
Equivalent to
print_flush followed by a new line.
val force_newline :
unit -> unit
Forces a newline in the current box. Not the normal way of pretty-printing, you
should prefer break hints.
val print_if_newline :
unit -> unit
Executes the next formatting command if the preceding line has just been split.
Otherwise, ignore the next formatting command.
=== Margin ===
val set_margin :
int -> unit
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. If
d is too
large, the right margin is set to the maximum admissible value (which is
greater than
10^10 ).
val get_margin :
unit -> int
Returns the position of the right margin.
=== Maximum indentation limit ===
val set_max_indent :
int -> unit
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. If
d is too large, the limit is set to the maximum
admissible value (which is greater than
10^10 ).
val get_max_indent :
unit -> int
Return the value of the maximum indentation limit (in characters).
=== Formatting depth: maximum number of boxes allowed before
ellipsis ===
val set_max_boxes :
int -> unit
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 smaller than 2.
val get_max_boxes :
unit -> int
Returns the maximum number of boxes allowed before ellipsis.
val over_max_boxes :
unit -> bool
Tests if the maximum number of boxes allowed have already been opened.
=== Advanced formatting ===
val open_hbox :
unit -> unit
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 :
int -> unit
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 :
int -> unit
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 :
int -> unit
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.
=== Tabulations ===
val open_tbox :
unit -> unit
Opens a tabulation box.
val close_tbox :
unit -> unit
Closes the most recently opened tabulation box.
val print_tbreak :
int -> int -> unit
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 :
unit -> unit
Sets a tabulation mark at the current insertion point.
val print_tab :
unit -> unit
print_tab () is equivalent to
print_tbreak 0 0 .
=== Ellipsis ===
val set_ellipsis_text :
string -> unit
Set the text of the ellipsis printed when too many boxes are opened (a single
dot,
. , by default).
val get_ellipsis_text :
unit -> string
Return the text of the ellipsis.
=== Semantics Tags ===
type tag =
string
=== Semantics tags (or simply 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 delimitation 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 drives 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 does 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. By default, tags
are not active, hence the output is not decorated with tag information.
Once set_tags is set to true, the pretty printer engine honours tags
and decorates the output accordingly. 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 drives 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 t is <t> and the closing marker </t> .
Default tag printing functions just do nothing. Tag marking and tag
printing functions are user definable and can be set by calling
set_formatter_tag_functions. ===
val open_tag :
tag -> unit
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 :
unit -> unit
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 :
bool -> unit
set_tags b turns on or off the treatment of tags (default is off).
val set_print_tags :
bool -> unit
val set_mark_tags :
bool -> unit
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 :
unit -> bool
val get_mark_tags :
unit -> bool
Return the current status of tags printing and tags marking.
=== Redirecting the standard formatter output ===
val set_formatter_out_channel :
Pervasives.out_channel -> unit
Redirect the pretty-printer output to the given channel. (All the output
functions of the standard formatter are set to the default output functions
printing to the given channel.)
val set_formatter_output_functions :
(string -> int -> int ->
unit) -> (unit -> unit) -> unit
set_formatter_output_functions out flush redirects the relevant
pretty-printer output functions to the functions
out and
flush .
The
out function performs the pretty-printer string output. It is called
with a string
s , a start position
p , and a number of
characters
n ; it is supposed to output characters
p to
p + n
- 1 of
s . The
flush function is called whenever the
pretty-printer is flushed (via conversion
%! , pretty-printing
indications
@? or
@. , or using low level function
print_flush or
print_newline ).
val get_formatter_output_functions :
unit -> (string -> int
-> int -> unit) * (unit -> unit)
Return the current output functions of the pretty-printer.
=== Changing the meaning of standard formatter pretty printing
===
=== The Format module is versatile enough to let you completely redefine
the meaning of pretty printing: you may provide your own functions to
define how to handle indentation, line breaking, and even printing of
all the characters that have to be printed! ===
val set_all_formatter_output_functions :
out:(string -> int ->
int -> unit) -> flush:(unit -> unit) ->
newline:(unit -> unit) -> spaces:(int -> unit) -> unit
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
outspace and
outnewline are normally
connected to
out and
flush : respective default values for
outspace and
outnewline are
out (String.make n ' ') 0 n
and
out \n 0 1 .
val get_all_formatter_output_functions :
unit -> (string
-> int -> int -> unit) * (unit -> unit) * (unit -> unit) *
(int -> unit)
Return the current output functions of the pretty-printer, including line
breaking and indentation functions. Useful to record the current setting and
restore it afterwards.
=== Changing the meaning of printing semantics tags ===
type formatter_tag_functions = {
mark_open_tag :
tag -> string ;
mark_close_tag :
tag -> string ;
print_open_tag :
tag -> unit ;
print_close_tag :
tag -> unit ;
}
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 :
formatter_tag_functions ->
unit
=== 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 t, the string t is passed to the opening tag marking
function (the mark_open_tag field of the record tag_funs), that must
return the opening tag marker for that name. When the next call to
close_tag () happens, the tag name t is sent back to the closing tag
marking function (the mark_close_tag field of record tag_funs), that
must return a closing tag marker for that name. The print_ field
of the record contains the functions that are called at tag opening and
tag closing time, to output regular material in the pretty-printer
queue. ===
val get_formatter_tag_functions :
unit ->
formatter_tag_functions
Return the current tag functions of the pretty-printer.
=== Multiple formatted output ===
type formatter
Abstract data corresponding to a pretty-printer (also called a formatter) and
all its machinery.
Defining new pretty-printers permits unrelated output of material in parallel on
several output channels. All the 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 a
Pervasives.out_channel output channel
oc , a new formatter
writing to that channel is simply 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 :
Pervasives.out_channel ->
formatter
formatter_of_out_channel oc returns a new formatter that writes to the
corresponding channel
oc .
val std_formatter :
formatter
The standard formatter used by the formatting functions above. It is defined as
formatter_of_out_channel stdout .
val err_formatter :
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 :
Buffer.t -> formatter
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 :
Buffer.t
The string buffer in which
str_formatter writes.
val str_formatter :
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 :
unit -> string
Returns the material printed with
str_formatter , flushes the formatter
and resets the corresponding buffer.
val make_formatter :
(string -> int -> int -> unit) ->
(unit -> unit) -> formatter
make_formatter out flush returns a new formatter that writes according to
the output function
out , and the flushing function
flush . For
instance, a formatter to the
Pervasives.out_channel oc is
returned by
make_formatter (Pervasives.output oc) (fun () ->
Pervasives.flush oc) .
=== Basic functions to use with formatters ===
val pp_open_hbox :
formatter -> unit -> unit
val pp_open_vbox :
formatter -> int -> unit
val pp_open_hvbox :
formatter -> int -> unit
val pp_open_hovbox :
formatter -> int -> unit
val pp_open_box :
formatter -> int -> unit
val pp_close_box :
formatter -> unit -> unit
val pp_open_tag :
formatter -> string -> unit
val pp_close_tag :
formatter -> unit -> unit
val pp_print_string :
formatter -> string -> unit
val pp_print_as :
formatter -> int -> string -> unit
val pp_print_int :
formatter -> int -> unit
val pp_print_float :
formatter -> float -> unit
val pp_print_char :
formatter -> char -> unit
val pp_print_bool :
formatter -> bool -> unit
val pp_print_break :
formatter -> int -> int -> unit
val pp_print_cut :
formatter -> unit -> unit
val pp_print_space :
formatter -> unit -> unit
val pp_force_newline :
formatter -> unit -> unit
val pp_print_flush :
formatter -> unit -> unit
val pp_print_newline :
formatter -> unit -> unit
val pp_print_if_newline :
formatter -> unit -> unit
val pp_open_tbox :
formatter -> unit -> unit
val pp_close_tbox :
formatter -> unit -> unit
val pp_print_tbreak :
formatter -> int -> int -> unit
val pp_set_tab :
formatter -> unit -> unit
val pp_print_tab :
formatter -> unit -> unit
val pp_set_tags :
formatter -> bool -> unit
val pp_set_print_tags :
formatter -> bool -> unit
val pp_set_mark_tags :
formatter -> bool -> unit
val pp_get_print_tags :
formatter -> unit -> bool
val pp_get_mark_tags :
formatter -> unit -> bool
val pp_set_margin :
formatter -> int -> unit
val pp_get_margin :
formatter -> unit -> int
val pp_set_max_indent :
formatter -> int -> unit
val pp_get_max_indent :
formatter -> unit -> int
val pp_set_max_boxes :
formatter -> int -> unit
val pp_get_max_boxes :
formatter -> unit -> int
val pp_over_max_boxes :
formatter -> unit -> bool
val pp_set_ellipsis_text :
formatter -> string -> unit
val pp_get_ellipsis_text :
formatter -> unit -> string
val pp_set_formatter_out_channel :
formatter ->
Pervasives.out_channel -> unit
val pp_set_formatter_output_functions :
formatter -> (string ->
int -> int -> unit) -> (unit -> unit) -> unit
val pp_get_formatter_output_functions :
formatter -> unit ->
(string -> int -> int -> unit) * (unit -> unit)
val pp_set_all_formatter_output_functions :
formatter ->
out:(string -> int -> int -> unit) -> flush:(unit ->
unit) -> newline:(unit -> unit) -> spaces:(int -> unit)
-> unit
val pp_get_all_formatter_output_functions :
formatter ->
unit -> (string -> int -> int -> unit) * (unit ->
unit) * (unit -> unit) * (int -> unit)
val pp_set_formatter_tag_functions :
formatter ->
formatter_tag_functions -> unit
val pp_get_formatter_tag_functions :
formatter -> unit ->
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
.
=== printf like functions for pretty-printing. ===
val fprintf :
formatter -> ('a, formatter, unit) Pervasives.format
-> 'a
=== fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN
according to the format string fmt, and outputs the resulting string on
the formatter ff. The format fmt 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 specific to the Format module. The pretty-printing
indication characters are introduced by a @ character, and their
meanings are: - @[: open a pretty-printing box. The type and offset of
the box may be optionally specified with the following syntax:
the < character, followed by an optional box type indication,
then an optional integer offset, and the closing > character. Box
type is one of h, v, hv, b, or hov, which stand respectively for an
horizontal box, a vertical box, an ``horizontal-vertical'' box, or an
``horizontal or vertical'' box (b standing for an ``horizontal or
vertical'' box demonstrating indentation and hov standing for a
regular``horizontal or vertical'' box). For instance, @[<hov 2>
opens an ``horizontal or vertical'' box with indentation 2 as obtained
with open_hovbox 2. For more details about boxes, see the various box
opening functions open_*box. - @]: close the most recently
opened pretty-printing box. - @,: output a good break as with print_cut
(). - @ : output a space, as with print_space (). - @\n: force a
newline, as with force_newline (). - @;: output a good break as with
print_break. The nspaces and offset parameters of the break may be
optionally specified with the following syntax: the < character,
followed by an integer nspaces value, then an integer offset, and a
closing > character. If no parameters are provided, the good break
defaults to a space. - @?: flush the pretty printer as with
print_flush (). This is equivalent to the conversion %!. - @.:
flush the pretty printer and output a new line, as with print_newline
(). - @<n>: print the following item as if it were of length
n. Hence, printf @<0>%s arg is equivalent to print_as 0 arg.
If @<n> is not followed by a conversion specification, then
the following character of the format is printed as if it were of
length n. - @{: open a tag. The name of the tag may be optionally
specified with the following syntax: the < character, followed by
an optional string specification, and the closing > character. The
string specification is any character string that does not contain
the closing character '>'. If omitted, the tag name defaults to
the empty string. For more details about tags, see the functions
open_tag and close_tag. - @}: close the most recently opened
tag. - @@: print a plain @ character. Example: printf @[%s@
%d@]@. x = 1 is equivalent to open_box (); print_string x = ;
print_space (); print_int 1; close_box (); print_newline (). It
prints x = 1 within a pretty-printing box. ===
val printf :
('a, formatter, unit) Pervasives.format -> 'a
Same as
fprintf above, but output on
std_formatter .
val eprintf :
('a, formatter, unit) Pervasives.format -> 'a
Same as
fprintf above, but output on
err_formatter .
val sprintf :
('a, unit, string) Pervasives.format -> 'a
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
sprintf to output material on a
single string, you should consider using
fprintf with the predefined
formatter
str_formatter and call
flush_str_formatter () to get
the final result.
Alternatively, you can use
Format.fprintf with a formatter writing to a
buffer of your own: flushing the formatter and the buffer at the end of
pretty-printing returns the desired string.
val ifprintf :
formatter -> ('a, formatter, unit) Pervasives.format
-> 'a
Same as
fprintf above, but does not print anything. Useful to ignore some
material when conditionally printing.
Since 3.10.0
=== Formatted output functions with continuations. ===
val kfprintf :
(formatter -> 'a) -> formatter -> ('b,
formatter, unit, 'a) Pervasives.format4 -> 'b
Same as
fprintf above, but instead of returning immediately, passes the
formatter to its first argument at the end of printing.
val ikfprintf :
(formatter -> 'a) -> formatter -> ('b,
formatter, unit, 'a) Pervasives.format4 -> 'b
Same as
kfprintf above, but does not print anything. Useful to ignore
some material when conditionally printing.
Since 3.12.0
val ksprintf :
(string -> 'a) -> ('b, unit, string, 'a)
Pervasives.format4 -> 'b
Same as
sprintf above, but instead of returning the string, passes it to
the first argument.
=== Deprecated ===
val bprintf :
Buffer.t -> ('a, formatter, unit) Pervasives.format
-> 'a
A deprecated and error prone function. Do not use it.
If you need to print to some buffer
b , you must first define a formatter
writing to
b , using
let to_b = formatter_of_buffer b ; then use
regular calls to
Format.fprintf on formatter
to_b .
val kprintf :
(string -> 'a) -> ('b, unit, string, 'a)
Pervasives.format4 -> 'b
A deprecated synonym for
ksprintf .