module Format:Pretty printing.sig
..end
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.en.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:
open_box 0
);print_cut ()
that outputs a
simple break hint, or by print_space ()
that outputs a space
indicating a break hint);print_int
and print_string
);close_box ()
to
close the box;print_newline ()
.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.
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
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
val print_float : float -> unit
val print_char : char -> unit
val print_bool : bool -> unit
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
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
val print_newline : unit -> unit
print_flush
followed by a new line.val force_newline : unit -> unit
val print_if_newline : unit -> unit
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
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
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
val over_max_boxes : unit -> bool
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.val open_tbox : unit -> unit
val close_tbox : unit -> unit
val print_tbreak : int -> int -> unit
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
val print_tab : unit -> unit
print_tab ()
is equivalent to print_tbreak 0 0
.val set_ellipsis_text : string -> unit
.
, by default).val get_ellipsis_text : unit -> string
typetag =
string
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.bool -> unit
: set_tags b
turns on or off the treatment of tags (default is off).bool -> unit
: 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.unit -> bool
: unit -> bool
: val set_formatter_out_channel : out_channel -> unit
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)
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)
type
formatter_tag_functions = {
|
mark_open_tag : |
|
mark_close_tag : |
|
print_open_tag : |
|
print_close_tag : |
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
type
formatter
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 : out_channel -> formatter
formatter_of_out_channel oc
returns a new formatter that
writes to the corresponding channel oc
.val std_formatter : formatter
formatter_of_out_channel stdout
.val err_formatter : formatter
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
str_formatter
writes.val str_formatter : formatter
stdbuf
string buffer.
str_formatter
is defined as formatter_of_buffer stdbuf
.val flush_str_formatter : unit -> string
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)
.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
formatter -> bool -> unit
: formatter -> bool -> unit
: formatter -> bool -> unit
: formatter -> unit -> bool
: 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 -> 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
print_string
is equal to pp_print_string std_formatter
.printf
like functions for pretty-printing.val fprintf : formatter -> ('a, formatter, unit) 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
prints arg
as a zero length string.
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.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.
Note: the old @@
``pretty-printing indication'' is now deprecated, since
it had no pretty-printing indication semantics. If you need to prevent
the pretty-printing indication interpretation of a @
character, simply
use the regular way to escape a character in format string: write %@
.
val printf : ('a, formatter, unit) format -> 'a
fprintf
above, but output on std_formatter
.val eprintf : ('a, formatter, unit) format -> 'a
fprintf
above, but output on err_formatter
.val sprintf : ('a, unit, string) format -> 'a
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) format -> 'a
fprintf
above, but does not print anything.
Useful to ignore some material when conditionally printing.val kfprintf : (formatter -> 'a) ->
formatter -> ('b, formatter, unit, 'a) format4 -> 'b
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) format4 -> 'b
kfprintf
above, but does not print anything.
Useful to ignore some material when conditionally printing.val ksprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
sprintf
above, but instead of returning the string,
passes it to the first argument.val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
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) format4 -> 'b
ksprintf
.