Provided by: ocaml-man_4.13.1-3ubuntu1_all 
NAME
Format - Pretty-printing.
Module
Module Format
Documentation
Module Format
: sig end
Pretty-printing.
This module implements a pretty-printing facility to format values within Format.boxes and
Format.tags combined with a set of Format.fpp . The pretty-printer splits lines at
specified Format.breaks , and indents lines according to the box structure. Similarly,
Format.tags can be used to decouple text presentation from its contents.
This pretty-printing facility is implemented as an overlay on top of abstract
Format.formatter which provide basic output functions. Some formatters are predefined,
notably:
- Format.std_formatter outputs to stdout
- Format.err_formatter outputs to stderr
Most functions in the Format module come in two variants: a short version that operates on
Format.std_formatter and the generic version prefixed by pp_ that takes a formatter as its
first argument.
More formatters can be created with Format.formatter_of_out_channel ,
Format.formatter_of_buffer , Format.formatter_of_symbolic_output_buffer or using
Format.formatter .
Introduction
You may consider this module as providing an extension to the printf facility to provide
automatic line splitting. The addition of pretty-printing annotations to your regular
printf format strings 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 pretty-printing box management and printing functions
provided by this module. This style is more basic but more verbose than the concise
fprintf format strings.
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 pretty-printing 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 pretty-printing box is open, display its material with basic printing functions
(e. g. print_int and print_string );
-when the material for a pretty-printing box has been printed, call close_box () to close
the box;
-at the end of pretty-printing, flush the pretty-printer to display all the remaining
material, e.g. evaluate print_newline () .
The behavior of pretty-printing commands is unspecified if there is no open
pretty-printing box. Each box opened by 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, each phrase is executed in the initial state of the standard
pretty-printer: after each phrase execution, the interactive system closes all open
pretty-printing boxes, flushes all pending text, and resets the standard pretty-printer.
Warning: mixing calls to pretty-printing functions of this module with calls to Stdlib low
level output functions is error prone.
The pretty-printing functions output material that is delayed in the pretty-printer queue
and stacks in order to compute proper line splitting. In contrast, basic I/O output
functions write directly in their output device. As a consequence, the output of a basic
I/O function may appear before the output of a pretty-printing function that has been
called before. For instance,
Stdlib.print_string "<";
Format.print_string "PRETTY";
Stdlib.print_string ">";
Format.print_string "TEXT";
leads to output <>PRETTYTEXT .
Formatters
type formatter
Abstract data corresponding to a pretty-printer (also called a formatter) and all its
machinery. See also Format.formatter .
Pretty-printing boxes
The pretty-printing engine uses the concepts of pretty-printing box and break hint to
drive indentation and line splitting behavior of the pretty-printer.
Each different pretty-printing box kind introduces a specific line splitting policy:
-within an horizontal box, break hints never split the line (but the line may be split in
a box nested deeper),
-within a vertical box, break hints always split the line,
-within an horizontal/vertical box, if the box fits on the current line then break hints
never split the line, otherwise break hint always split the line,
-within a compacting box, a break hint never splits the line, unless there is no more room
on the current line.
Note that line splitting policy is box specific: the policy of a box does not rule the
policy of inner boxes. For instance, if a vertical box is nested in an horizontal box, all
break hints within the vertical box will split the line.
Moreover, opening a box after the Format.maxindent splits the line whether or not the box
would end up fitting on the line.
val pp_open_box : formatter -> int -> unit
val open_box : int -> unit
pp_open_box ppf d opens a new compacting pretty-printing box with offset d in the
formatter ppf .
Within this box, the pretty-printer prints as much as possible material on every line.
A break hint splits the line if there is no more room on the line to print the remainder
of the box.
Within this box, the pretty-printer emphasizes the box structure: if a structural box does
not fit fully on a simple line, a break hint also splits the line if the splitting ``moves
to the left'' (i.e. the new line gets an indentation smaller than the one of the current
line).
This box is the general purpose pretty-printing box.
If the pretty-printer splits the line in the box, offset d is added to the current
indentation.
val pp_close_box : formatter -> unit -> unit
val close_box : unit -> unit
Closes the most recently open pretty-printing box.
val pp_open_hbox : formatter -> unit -> unit
val open_hbox : unit -> unit
pp_open_hbox ppf () opens a new 'horizontal' pretty-printing box.
This box prints material on a single line.
Break hints in a horizontal box never split the line. (Line splitting may still occur
inside boxes nested deeper).
val pp_open_vbox : formatter -> int -> unit
val open_vbox : int -> unit
pp_open_vbox ppf d opens a new 'vertical' pretty-printing box with offset d .
This box prints material on as many lines as break hints in the box.
Every break hint in a vertical box splits the line.
If the pretty-printer splits the line in the box, d is added to the current indentation.
val pp_open_hvbox : formatter -> int -> unit
val open_hvbox : int -> unit
pp_open_hvbox ppf d opens a new 'horizontal/vertical' pretty-printing box with offset d .
This box behaves as an horizontal box if it fits on a single line, otherwise it behaves as
a vertical box.
If the pretty-printer splits the line in the box, d is added to the current indentation.
val pp_open_hovbox : formatter -> int -> unit
val open_hovbox : int -> unit
pp_open_hovbox ppf d opens a new 'horizontal-or-vertical' pretty-printing box with offset
d .
This box prints material as much as possible on every line.
A break hint splits the line if there is no more room on the line to print the remainder
of the box.
If the pretty-printer splits the line in the box, d is added to the current indentation.
Formatting functions
val pp_print_string : formatter -> string -> unit
val print_string : string -> unit
pp_print_string ppf s prints s in the current pretty-printing box.
val pp_print_bytes : formatter -> bytes -> unit
val print_bytes : bytes -> unit
pp_print_bytes ppf b prints b in the current pretty-printing box.
Since 4.13.0
val pp_print_as : formatter -> int -> string -> unit
val print_as : int -> string -> unit
pp_print_as ppf len s prints s in the current pretty-printing box. The pretty-printer
formats s as if it were of length len .
val pp_print_int : formatter -> int -> unit
val print_int : int -> unit
Print an integer in the current pretty-printing box.
val pp_print_float : formatter -> float -> unit
val print_float : float -> unit
Print a floating point number in the current pretty-printing box.
val pp_print_char : formatter -> char -> unit
val print_char : char -> unit
Print a character in the current pretty-printing box.
val pp_print_bool : formatter -> bool -> unit
val print_bool : bool -> unit
Print a boolean in the current pretty-printing box.
Break hints
A 'break hint' tells the pretty-printer to output some space or split the line whichever
way is more appropriate to the current pretty-printing box splitting rules.
Break hints are used to separate printing items and are mandatory to let the
pretty-printer correctly split lines and indent items.
Simple break hints are:
-the 'space': output a space or split the line if appropriate,
-the 'cut': split the line if appropriate.
Note: the notions of space and line splitting are abstract for the pretty-printing engine,
since those notions can be completely redefined by the programmer. However, in the
pretty-printer default setting, ``output a space'' simply means printing a space character
(ASCII code 32) and ``split the line'' means printing a newline character (ASCII code 10).
val pp_print_space : formatter -> unit -> unit
val print_space : unit -> unit
pp_print_space ppf () emits a 'space' break hint: the pretty-printer may split the line at
this point, otherwise it prints one space.
pp_print_space ppf () is equivalent to pp_print_break ppf 1 0 .
val pp_print_cut : formatter -> unit -> unit
val print_cut : unit -> unit
pp_print_cut ppf () emits a 'cut' break hint: the pretty-printer may split the line at
this point, otherwise it prints nothing.
pp_print_cut ppf () is equivalent to pp_print_break ppf 0 0 .
val pp_print_break : formatter -> int -> int -> unit
val print_break : int -> int -> unit
pp_print_break ppf nspaces offset emits a 'full' break hint: the pretty-printer may split
the line at this point, otherwise it prints nspaces spaces.
If the pretty-printer splits the line, offset is added to the current indentation.
val pp_print_custom_break : formatter -> fits:string * int * string -> breaks:string * int
* string -> unit
pp_print_custom_break ppf ~fits:(s1, n, s2) ~breaks:(s3, m, s4) emits a custom break hint:
the pretty-printer may split the line at this point.
If it does not split the line, then the s1 is emitted, then n spaces, then s2 .
If it splits the line, then it emits the s3 string, then an indent (according to the box
rules), then an offset of m spaces, then the s4 string.
While n and m are handled by formatter_out_functions.out_indent , the strings will be
handled by formatter_out_functions.out_string . This allows for a custom formatter that
handles indentation distinctly, for example, outputs <br/> tags or entities.
The custom break is useful if you want to change which visible (non-whitespace) characters
are printed in case of break or no break. For example, when printing a list
[a; b; c]
trailing semicolon when it is printed vertically:
[
a;
b;
c;
]
You can do this as follows:
printf "@[<v 0>[@;<0 2>@[<v 0>a;@,b;@,c@]%t]@]@\n"
(pp_print_custom_break ~fits:("", 0, "") ~breaks:(";", 0, ""))
Since 4.08.0
val pp_force_newline : formatter -> unit -> unit
val force_newline : unit -> unit
Force a new line in the current pretty-printing box.
The pretty-printer must split the line at this point,
Not the normal way of pretty-printing, since imperative line splitting may interfere with
current line counters and box size calculation. Using break hints within an enclosing
vertical box is a better alternative.
val pp_print_if_newline : formatter -> unit -> unit
val print_if_newline : unit -> unit
Execute the next formatting command if the preceding line has just been split. Otherwise,
ignore the next formatting command.
Pretty-printing termination
val pp_print_flush : formatter -> unit -> unit
val print_flush : unit -> unit
End of pretty-printing: resets the pretty-printer to initial state.
All open pretty-printing boxes are closed, all pending text is printed. In addition, the
pretty-printer low level output device is flushed to ensure that all pending text is
really displayed.
Note: never use print_flush in the normal course of a pretty-printing routine, since the
pretty-printer uses a complex buffering machinery to properly indent the output; manually
flushing those buffers at random would conflict with the pretty-printer strategy and
result to poor rendering.
Only consider using print_flush when displaying all pending material is mandatory (for
instance in case of interactive use when you want the user to read some text) and when
resetting the pretty-printer state will not disturb further pretty-printing.
Warning: If the output device of the pretty-printer is an output channel, repeated calls
to print_flush means repeated calls to flush to flush the out channel; these explicit
flush calls could foil the buffering strategy of output channels and could dramatically
impact efficiency.
val pp_print_newline : formatter -> unit -> unit
val print_newline : unit -> unit
End of pretty-printing: resets the pretty-printer to initial state.
All open pretty-printing boxes are closed, all pending text is printed.
Equivalent to Format.print_flush followed by a new line. See corresponding words of
caution for Format.print_flush .
Note: this is not the normal way to output a new line; the preferred method is using break
hints within a vertical pretty-printing box.
Margin
val pp_set_margin : formatter -> int -> unit
val set_margin : int -> unit
pp_set_margin ppf d sets the right margin to d (in characters): the pretty-printer splits
lines that overflow the right margin according to the break hints given. Setting the
margin to d means that the formatting engine aims at printing at most d-1 characters per
line. 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 ^ 9 ). If d is less than the
current maximum indentation limit, the maximum indentation limit is decreased while trying
to preserve a minimal ratio max_indent/margin>=50% and if possible the current difference
margin - max_indent .
See also Format.pp_set_geometry .
val pp_get_margin : formatter -> unit -> int
val get_margin : unit -> int
Returns the position of the right margin.
Maximum indentation limit
val pp_set_max_indent : formatter -> int -> unit
val set_max_indent : int -> unit
pp_set_max_indent ppf d sets the maximum indentation limit of lines to d (in characters):
once this limit is reached, new pretty-printing boxes are rejected to the left, unless the
enclosing box fully fits on the current line. As an illustration,
set_margin 10; set_max_indent 5; printf "@[123456@[7@]89A@]@."
yields
123456
789A
because the nested box "@[7@]" is opened after the maximum indentation limit ( 7>5 ) and
its parent box does not fit on the current line. Either decreasing the length of the
parent box to make it fit on a line:
printf "@[123456@[7@]89@]@."
or opening an intermediary box before the maximum indentation limit which fits on the
current line
printf "@[123@[456@[7@]89@]A@]@."
avoids the rejection to the left of the inner boxes and print respectively "123456789" and
"123456789A" . Note also that vertical boxes never fit on a line whereas horizontal boxes
always fully fit on the current line. Opening a box may split a line whereas the contents
may have fit. If this behavior is problematic, it can be curtailed by setting the maximum
indentation limit to margin - 1 . Note that setting the maximum indentation limit to
margin is invalid.
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 ^ 9 ).
If d is greater or equal than the current margin, it is ignored, and the current maximum
indentation limit is kept.
See also Format.pp_set_geometry .
val pp_get_max_indent : formatter -> unit -> int
val get_max_indent : unit -> int
Return the maximum indentation limit (in characters).
Geometry
Geometric functions can be used to manipulate simultaneously the coupled variables, margin
and maxixum indentation limit.
type geometry = {
max_indent : int ;
margin : int ;
}
val check_geometry : geometry -> bool
Check if the formatter geometry is valid: 1 < max_indent < margin
val pp_set_geometry : formatter -> max_indent:int -> margin:int -> unit
val set_geometry : max_indent:int -> margin:int -> unit
val pp_safe_set_geometry : formatter -> max_indent:int -> margin:int -> unit
val safe_set_geometry : max_indent:int -> margin:int -> unit
pp_set_geometry ppf ~max_indent ~margin sets both the margin and maximum indentation limit
for ppf .
When 1 < max_indent < margin , pp_set_geometry ppf ~max_indent ~margin is equivalent to
pp_set_margin ppf margin; pp_set_max_indent ppf max_indent ; and avoids the subtly
incorrect pp_set_max_indent ppf max_indent; pp_set_margin ppf margin ;
Outside of this domain, pp_set_geometry raises an invalid argument exception whereas
pp_safe_set_geometry does nothing.
Since 4.08.0
val pp_update_geometry : formatter -> (geometry -> geometry) -> unit
pp_update_geometry ppf (fun geo -> { geo with ... }) lets you update a formatter's
geometry in a way that is robust to extension of the geometry record with new fields.
Raises an invalid argument exception if the returned geometry does not satisfy
Format.check_geometry .
Since 4.11.0
val update_geometry : (geometry -> geometry) -> unit
val pp_get_geometry : formatter -> unit -> geometry
val get_geometry : unit -> geometry
Return the current geometry of the formatter
Since 4.08.0
Maximum formatting depth
The maximum formatting depth is the maximum number of pretty-printing boxes simultaneously
open.
Material inside boxes nested deeper is printed as an ellipsis (more precisely as the text
returned by Format.get_ellipsis_text () ).
val pp_set_max_boxes : formatter -> int -> unit
val set_max_boxes : int -> unit
pp_set_max_boxes ppf max sets the maximum number of pretty-printing boxes simultaneously
open.
Material inside boxes nested deeper is printed as an ellipsis (more precisely as the text
returned by Format.get_ellipsis_text () ).
Nothing happens if max is smaller than 2.
val pp_get_max_boxes : formatter -> unit -> int
val get_max_boxes : unit -> int
Returns the maximum number of pretty-printing boxes allowed before ellipsis.
val pp_over_max_boxes : formatter -> unit -> bool
val over_max_boxes : unit -> bool
Tests if the maximum number of pretty-printing boxes allowed have already been opened.
Tabulation boxes
A tabulation box prints material on lines divided into cells of fixed length. A tabulation
box provides a simple way to display vertical columns of left adjusted text.
This box features command set_tab to define cell boundaries, and command print_tab to move
from cell to cell and split the line when there is no more cells to print on the line.
Note: printing within tabulation box is line directed, so arbitrary line splitting inside
a tabulation box leads to poor rendering. Yet, controlled use of tabulation boxes allows
simple printing of columns within module Format .
val pp_open_tbox : formatter -> unit -> unit
val open_tbox : unit -> unit
open_tbox () opens a new tabulation box.
This box prints lines separated into cells of fixed width.
Inside a tabulation box, special tabulation markers defines points of interest on the line
(for instance to delimit cell boundaries). Function Format.set_tab sets a tabulation
marker at insertion point.
A tabulation box features specific tabulation breaks to move to next tabulation marker or
split the line. Function Format.print_tbreak prints a tabulation break.
val pp_close_tbox : formatter -> unit -> unit
val close_tbox : unit -> unit
Closes the most recently opened tabulation box.
val pp_set_tab : formatter -> unit -> unit
val set_tab : unit -> unit
Sets a tabulation marker at current insertion point.
val pp_print_tab : formatter -> unit -> unit
val print_tab : unit -> unit
print_tab () emits a 'next' tabulation break hint: if not already set on a tabulation
marker, the insertion point moves to the first tabulation marker on the right, or the
pretty-printer splits the line and insertion point moves to the leftmost tabulation
marker.
It is equivalent to print_tbreak 0 0 .
val pp_print_tbreak : formatter -> int -> int -> unit
val print_tbreak : int -> int -> unit
print_tbreak nspaces offset emits a 'full' tabulation break hint.
If not already set on a tabulation marker, the insertion point moves to the first
tabulation marker on the right and the pretty-printer prints nspaces spaces.
If there is no next tabulation marker on the right, the pretty-printer splits the line at
this point, then insertion point moves to the leftmost tabulation marker of the box.
If the pretty-printer splits the line, offset is added to the current indentation.
Ellipsis
val pp_set_ellipsis_text : formatter -> string -> unit
val set_ellipsis_text : string -> unit
Set the text of the ellipsis printed when too many pretty-printing boxes are open (a
single dot, . , by default).
val pp_get_ellipsis_text : formatter -> unit -> string
val get_ellipsis_text : unit -> string
Return the text of the ellipsis.
Semantic tags
type stag = ..
Semantic tags (or simply tags) are user's defined annotations to associate user's specific
operations to printed entities.
Common usage of semantic tags is text decoration to get specific font or text size
rendering for a display device, or marking delimitation of entities (e.g. HTML or TeX
elements or terminal escape sequences). More sophisticated usage of semantic tags could
handle dynamic modification of the pretty-printer behavior to properly print the material
within some specific tags. For instance, we can define an RGB tag like so:
type stag += RGB of {r:int;g:int;b:int}
In order to properly delimit printed entities, a semantic tag must be opened before and
closed after the entity. Semantic tags must be properly nested like parentheses using
Format.pp_open_stag and Format.pp_close_stag .
Tag specific operations occur any time a tag is opened or closed, At each occurrence, two
kinds of operations are performed tag-marking and tag-printing:
-The tag-marking operation is the simpler tag specific operation: it simply writes a tag
specific string into the output device of the formatter. Tag-marking does not interfere
with line-splitting computation.
-The tag-printing operation is the more involved tag specific operation: it can print
arbitrary material to the formatter. Tag-printing is tightly linked to the current
pretty-printer operations.
Roughly speaking, tag-marking is commonly used to get a better rendering of texts in the
rendering device, while tag-printing allows fine tuning of printing routines to print the
same entity differently according to the semantic tags (i.e. print additional material or
even omit parts of the output).
More precisely: when a semantic tag is opened or closed then both and successive
'tag-printing' and 'tag-marking' operations occur:
-Tag-printing a semantic tag means calling the formatter specific function print_open_stag
(resp. print_close_stag ) 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 splitting computation).
-Tag-marking a semantic tag means calling the formatter specific function mark_open_stag
(resp. mark_close_stag ) with the name of the tag as argument: that tag-marking function
can then return the 'tag-opening marker' (resp. `tag-closing marker') for direct output
into the output device of the formatter.
Being written directly into the output device of the formatter, semantic tag marker
strings are not considered as part of the printing material that drives line splitting (in
other words, the length of the strings corresponding to tag markers is considered as zero
for line splitting).
Thus, semantic tag handling is in some sense transparent to pretty-printing and does not
interfere with usual indentation. 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 honors tags and decorates the
output accordingly.
Default tag-marking functions behave the HTML way: Format.tag are enclosed in "<" and ">"
while other tags are ignored; hence, opening marker for tag string "t" is "<t>" and
closing marker is "</t>" .
Default tag-printing functions just do nothing.
Tag-marking and tag-printing functions are user definable and can be set by calling
Format.set_formatter_stag_functions .
Semantic tag operations may be set on or off with Format.set_tags . Tag-marking
operations may be set on or off with Format.set_mark_tags . Tag-printing operations may
be set on or off with Format.set_print_tags .
Since 4.08.0
type tag = string
type stag +=
| String_tag of tag (* String_tag s is a string tag s . String tags can be inserted
either by explicitly using the constructor String_tag or by using the dedicated format
syntax "@{<s> ... @}" .
Since 4.08.0
*)
val pp_open_stag : formatter -> stag -> unit
val open_stag : stag -> unit
pp_open_stag ppf t opens the semantic tag named t .
The print_open_stag tag-printing function of the formatter is called with t as argument;
then the opening tag marker for t , as given by mark_open_stag t , is written into the
output device of the formatter.
Since 4.08.0
val pp_close_stag : formatter -> unit -> unit
val close_stag : unit -> unit
pp_close_stag ppf () closes the most recently opened semantic tag t .
The closing tag marker, as given by mark_close_stag t , is written into the output device
of the formatter; then the print_close_stag tag-printing function of the formatter is
called with t as argument.
Since 4.08.0
val pp_set_tags : formatter -> bool -> unit
val set_tags : bool -> unit
pp_set_tags ppf b turns on or off the treatment of semantic tags (default is off).
val pp_set_print_tags : formatter -> bool -> unit
val set_print_tags : bool -> unit
pp_set_print_tags ppf b turns on or off the tag-printing operations.
val pp_set_mark_tags : formatter -> bool -> unit
val set_mark_tags : bool -> unit
pp_set_mark_tags ppf b turns on or off the tag-marking operations.
val pp_get_print_tags : formatter -> unit -> bool
val get_print_tags : unit -> bool
Return the current status of tag-printing operations.
val pp_get_mark_tags : formatter -> unit -> bool
val get_mark_tags : unit -> bool
Return the current status of tag-marking operations.
val pp_set_formatter_out_channel : formatter -> out_channel -> unit
Redirecting the standard formatter output
val set_formatter_out_channel : out_channel -> unit
Redirect the standard 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.)
set_formatter_out_channel is equivalent to Format.pp_set_formatter_out_channel
std_formatter .
val pp_set_formatter_output_functions : formatter -> (string -> int -> int -> unit) ->
(unit -> unit) -> unit
val set_formatter_output_functions : (string -> int -> int -> unit) -> (unit -> unit) ->
unit
pp_set_formatter_output_functions ppf out flush redirects the standard pretty-printer
output functions to the functions out and flush .
The out function performs all 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 %! ,
or pretty-printing indications @? or @. , or using low level functions print_flush or
print_newline ).
val pp_get_formatter_output_functions : formatter -> unit -> (string -> int -> int ->
unit) * (unit -> unit)
val get_formatter_output_functions : unit -> (string -> int -> int -> unit) * (unit ->
unit)
Return the current output functions of the standard pretty-printer.
Redefining formatter output
The Format module is versatile enough to let you completely redefine the meaning of
pretty-printing output: you may provide your own functions to define how to handle
indentation, line splitting, and even printing of all the characters that have to be
printed!
Redefining output functions
type formatter_out_functions = {
out_string : string -> int -> int -> unit ;
out_flush : unit -> unit ;
out_newline : unit -> unit ;
out_spaces : int -> unit ;
out_indent : int -> unit ; (* .B "Since" 4.06.0
*)
}
The set of output functions specific to a formatter:
-the out_string function performs all 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 out_flush function flushes the pretty-printer output device.
- out_newline is called to open a new line when the pretty-printer splits the line.
-the out_spaces function outputs spaces when a break hint leads to spaces instead of a
line split. It is called with the number of spaces to output.
-the out_indent function performs new line indentation when the pretty-printer splits the
line. It is called with the indentation value of the new line.
By default:
-fields out_string and out_flush are output device specific; (e.g. output_string and
flush for a out_channel device, or Buffer.add_substring and ignore for a Buffer.t output
device),
-field out_newline is equivalent to out_string "\n" 0 1 ;
-fields out_spaces and out_indent are equivalent to out_string (String.make n ' ') 0 n .
Since 4.01.0
val pp_set_formatter_out_functions : formatter -> formatter_out_functions -> unit
val set_formatter_out_functions : formatter_out_functions -> unit
pp_set_formatter_out_functions ppf out_funs Set all the pretty-printer output functions of
ppf to those of argument out_funs ,
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).
Reasonable defaults for functions out_spaces and out_newline are respectively
out_funs.out_string (String.make n ' ') 0 n and out_funs.out_string "\n" 0 1 .
Since 4.01.0
val pp_get_formatter_out_functions : formatter -> unit -> formatter_out_functions
val get_formatter_out_functions : unit -> formatter_out_functions
Return the current output functions of the pretty-printer, including line splitting and
indentation functions. Useful to record the current setting and restore it afterwards.
Since 4.01.0
Redefining semantic tag operations
type formatter_stag_functions = {
mark_open_stag : stag -> string ;
mark_close_stag : stag -> string ;
print_open_stag : stag -> unit ;
print_close_stag : stag -> unit ;
}
The semantic 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 write 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.
Since 4.08.0
val pp_set_formatter_stag_functions : formatter -> formatter_stag_functions -> unit
val set_formatter_stag_functions : formatter_stag_functions -> unit
pp_set_formatter_stag_functions ppf tag_funs changes the meaning of opening and closing
semantic tag operations to use the functions in tag_funs when printing on ppf .
When opening a semantic tag with name t , the string t is passed to the opening
tag-marking function (the mark_open_stag field of the record tag_funs ), that must return
the opening tag marker for that name. When the next call to close_stag () happens, the
semantic tag name t is sent back to the closing tag-marking function (the mark_close_stag
field of record tag_funs ), that must return a closing tag marker for that name.
The print_ field of the record contains the tag-printing functions that are called at tag
opening and tag closing time, to output regular material in the pretty-printer queue.
Since 4.08.0
val pp_get_formatter_stag_functions : formatter -> unit -> formatter_stag_functions
val get_formatter_stag_functions : unit -> formatter_stag_functions
Return the current semantic tag operation functions of the standard pretty-printer.
Since 4.08.0
Defining formatters
Defining new formatters permits unrelated output of material in parallel on several output
devices. All the parameters of a formatter are local to the formatter: right margin,
maximum indentation limit, maximum number of pretty-printing boxes simultaneously open,
ellipsis, and so on, are specific to each formatter and may be fixed independently.
For instance, given a Buffer.t buffer b , Format.formatter_of_buffer b returns a new
formatter using buffer b as its output device. Similarly, given a out_channel output
channel oc , Format.formatter_of_out_channel oc returns a new formatter using channel oc
as its output device.
Alternatively, given out_funs , a complete set of output functions for a formatter, then
Format.formatter_of_out_functions out_funs computes a new formatter using those functions
for output.
val formatter_of_out_channel : out_channel -> formatter
formatter_of_out_channel oc returns a new formatter writing to the corresponding output
channel oc .
val std_formatter : formatter
The standard formatter to write to standard output.
It is defined as Format.formatter_of_out_channel stdout .
val err_formatter : formatter
A formatter to write to standard error.
It is defined as Format.formatter_of_out_channel stderr .
val formatter_of_buffer : Buffer.t -> formatter
formatter_of_buffer b returns a new formatter writing to buffer b . At the end of
pretty-printing, the formatter must be flushed using Format.pp_print_flush or
Format.pp_print_newline , to print all the pending material into the buffer.
val stdbuf : Buffer.t
The string buffer in which str_formatter writes.
val str_formatter : formatter
A formatter to output to the Format.stdbuf string buffer.
str_formatter is defined as Format.formatter_of_buffer Format.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 outputs with function out , and
flushes with function flush .
For instance,
make_formatter
(Stdlib.output oc)
(fun () -> Stdlib.flush oc)
returns a formatter to the out_channel oc .
val formatter_of_out_functions : formatter_out_functions -> formatter
formatter_of_out_functions out_funs returns a new formatter that writes with the set of
output functions out_funs .
See definition of type Format.formatter_out_functions for the meaning of argument out_funs
.
Since 4.06.0
Symbolic pretty-printing
Symbolic pretty-printing is pretty-printing using a symbolic formatter, i.e. a formatter
that outputs symbolic pretty-printing items.
When using a symbolic formatter, all regular pretty-printing activities occur but output
material is symbolic and stored in a buffer of output items. At the end of
pretty-printing, flushing the output buffer allows post-processing of symbolic output
before performing low level output operations.
In practice, first define a symbolic output buffer b using:
- let sob = make_symbolic_output_buffer () . Then define a symbolic formatter with:
- let ppf = formatter_of_symbolic_output_buffer sob
Use symbolic formatter ppf as usual, and retrieve symbolic items at end of pretty-printing
by flushing symbolic output buffer sob with:
- flush_symbolic_output_buffer sob .
type symbolic_output_item =
| Output_flush (* symbolic flush command
*)
| Output_newline (* symbolic newline command
*)
| Output_string of string
(* Output_string s : symbolic output for string s
*)
| Output_spaces of int
(* Output_spaces n : symbolic command to output n spaces
*)
| Output_indent of int
(* Output_indent i : symbolic indentation of size i
*)
Items produced by symbolic pretty-printers
Since 4.06.0
type symbolic_output_buffer
The output buffer of a symbolic pretty-printer.
Since 4.06.0
val make_symbolic_output_buffer : unit -> symbolic_output_buffer
make_symbolic_output_buffer () returns a fresh buffer for symbolic output.
Since 4.06.0
val clear_symbolic_output_buffer : symbolic_output_buffer -> unit
clear_symbolic_output_buffer sob resets buffer sob .
Since 4.06.0
val get_symbolic_output_buffer : symbolic_output_buffer -> symbolic_output_item list
get_symbolic_output_buffer sob returns the contents of buffer sob .
Since 4.06.0
val flush_symbolic_output_buffer : symbolic_output_buffer -> symbolic_output_item list
flush_symbolic_output_buffer sob returns the contents of buffer sob and resets buffer sob
. flush_symbolic_output_buffer sob is equivalent to let items =
get_symbolic_output_buffer sob in
clear_symbolic_output_buffer sob; items
Since 4.06.0
val add_symbolic_output_item : symbolic_output_buffer -> symbolic_output_item -> unit
add_symbolic_output_item sob itm adds item itm to buffer sob .
Since 4.06.0
val formatter_of_symbolic_output_buffer : symbolic_output_buffer -> formatter
formatter_of_symbolic_output_buffer sob returns a symbolic formatter that outputs to
symbolic_output_buffer sob .
Since 4.06.0
Convenience formatting functions.
val pp_print_list : ?pp_sep:(formatter -> unit -> unit) -> (formatter -> 'a -> unit) ->
formatter -> 'a list -> unit
pp_print_list ?pp_sep pp_v ppf l prints items of list l , using pp_v to print each item,
and calling pp_sep between items ( pp_sep defaults to Format.pp_print_cut . Does nothing
on empty lists.
Since 4.02.0
val pp_print_seq : ?pp_sep:(formatter -> unit -> unit) -> (formatter -> 'a -> unit) ->
formatter -> 'a Seq.t -> unit
pp_print_seq ?pp_sep pp_v ppf s prints items of sequence s , using pp_v to print each
item, and calling pp_sep between items ( pp_sep defaults to Format.pp_print_cut . Does
nothing on empty sequences.
This function does not terminate on infinite sequences.
Since 4.12
val pp_print_text : formatter -> string -> unit
pp_print_text ppf s prints s with spaces and newlines respectively printed using
Format.pp_print_space and Format.pp_force_newline .
Since 4.02.0
val pp_print_option : ?none:(formatter -> unit -> unit) -> (formatter -> 'a -> unit) ->
formatter -> 'a option -> unit
pp_print_option ?none pp_v ppf o prints o on ppf using pp_v if o is Some v and none if it
is None . none prints nothing by default.
Since 4.08
val pp_print_result : ok:(formatter -> 'a -> unit) -> error:(formatter -> 'e -> unit) ->
formatter -> ('a, 'e) result -> unit
pp_print_result ~ok ~error ppf r prints r on ppf using ok if r is Ok _ and error if r is
Error _ .
Since 4.08
val pp_print_either : left:(formatter -> 'a -> unit) -> right:(formatter -> 'b -> unit) ->
formatter -> ('a, 'b) Either.t -> unit
pp_print_either ~left ~right ppf e prints e on ppf using left if e is Either.Left _ and
right if e is Either.Right _ .
Since 4.13
Formatted pretty-printing
Module Format provides a complete set of printf like functions for pretty-printing using
format string specifications.
Specific annotations may be added in the format strings to give pretty-printing commands
to the pretty-printing engine.
Those annotations are introduced in the format strings using the @ character. For
instance, @ means a space break, @, means a cut, @[ opens a new box, and @] closes the
last open box.
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 string 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. Pretty-printing
box type is one of h , v , hv , b , or hov . ' h ' stands for an 'horizontal'
pretty-printing box, ' v ' stands for a 'vertical' pretty-printing box, ' hv ' stands for
an 'horizontal/vertical' pretty-printing box, ' b ' stands for an 'horizontal-or-vertical'
pretty-printing box demonstrating indentation, ' hov ' stands a simple
'horizontal-or-vertical' pretty-printing box. For instance, @[<hov 2> opens an
'horizontal-or-vertical' pretty-printing box with indentation 2 as obtained with
open_hovbox 2 . For more details about pretty-printing boxes, see the various box opening
functions open_*box .
- @] : close the most recently opened pretty-printing box.
- @, : output a 'cut' break hint, as with print_cut () .
- @ : output a 'space' break hint, as with print_space () .
- @; : output a 'full' break hint as with print_break . The nspaces and offset parameters
of the break hint 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' break hint.
- @. : flush the pretty-printer and split the 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 semantic 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 semantic tags, see the functions Format.open_stag and
Format.close_stag .
- @} : close the most recently opened semantic tag.
- @? : flush the pretty-printer as with print_flush () . This is equivalent to the
conversion %! .
- @\n : force a newline, as with force_newline () , not the normal way of pretty-printing,
you should prefer using break hints inside a vertical pretty-printing box.
Note: To prevent the interpretation of a @ character as a pretty-printing indication,
escape it with a % character. Old quotation mode @@ is deprecated since it is not
compatible with formatted input interpretation of 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
'horizontal-or-vertical' box.
val printf : ('a, formatter, unit) format -> 'a
Same as fprintf above, but output on std_formatter .
val eprintf : ('a, formatter, unit) format -> 'a
Same as fprintf above, but output on err_formatter .
val sprintf : ('a, unit, string) 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 asprintf : ('a, formatter, unit, string) format4 -> 'a
Same as printf above, but instead of printing on a formatter, returns a string containing
the result of formatting the arguments. The type of asprintf is general enough to
interact nicely with %a conversions.
Since 4.01.0
val dprintf : ('a, formatter, unit, formatter -> unit) format4 -> 'a
Same as Format.fprintf , except the formatter is the last argument. dprintf "..." a b c
is a function of type formatter -> unit which can be given to a format specifier %t .
This can be used as a replacement for Format.asprintf to delay formatting decisions. Using
the string returned by Format.asprintf in a formatting context forces formatting decisions
to be taken in isolation, and the final string may be created prematurely. Format.dprintf
allows delay of formatting decisions until the final formatting context is known. For
example:
let t = Format.dprintf "%i@ %i@ %i" 1 2 3 in
...
Format.printf "@[<v>%t@]" t
Since 4.08.0
val ifprintf : formatter -> ('a, formatter, unit) format -> 'a
Same as fprintf above, but does not print anything. Useful to ignore some material when
conditionally printing.
Since 3.10.0
Formatted Pretty-Printing with continuations.
val kfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit, 'a) format4 -> 'b
Same as fprintf above, but instead of returning immediately, passes the formatter to its
first argument at the end of printing.
val kdprintf : ((formatter -> unit) -> 'a) -> ('b, formatter, unit, 'a) format4 -> 'b
Same as Format.dprintf above, but instead of returning immediately, passes the suspended
printer to its first argument at the end of printing.
Since 4.08.0
val ikfprintf : (formatter -> 'a) -> formatter -> ('b, formatter, unit, 'a) 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) format4 -> 'b
Same as sprintf above, but instead of returning the string, passes it to the first
argument.
val kasprintf : (string -> 'a) -> ('b, formatter, unit, 'a) format4 -> 'b
Same as asprintf above, but instead of returning the string, passes it to the first
argument.
Since 4.03
Deprecated
val bprintf : Buffer.t -> ('a, formatter, unit) format -> 'a
Deprecated. This function is error prone. Do not use it. This function is neither
compositional nor incremental, since it flushes the pretty-printer queue at each call.
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 with
formatter to_b .
val kprintf : (string -> 'a) -> ('b, unit, string, 'a) format4 -> 'b
Deprecated. An alias for ksprintf .
val set_all_formatter_output_functions : out:(string -> int -> int -> unit) -> flush:(unit
-> unit) -> newline:(unit -> unit) -> spaces:(int -> unit) -> unit
Deprecated. Subsumed by set_formatter_out_functions .
val get_all_formatter_output_functions : unit -> (string -> int -> int -> unit) * (unit ->
unit) * (unit -> unit) * (int -> unit)
Deprecated. Subsumed by get_formatter_out_functions .
val pp_set_all_formatter_output_functions : formatter -> out:(string -> int -> int ->
unit) -> flush:(unit -> unit) -> newline:(unit -> unit) -> spaces:(int -> unit) -> unit
Deprecated. Subsumed by pp_set_formatter_out_functions .
val pp_get_all_formatter_output_functions : formatter -> unit -> (string -> int -> int ->
unit) * (unit -> unit) * (unit -> unit) * (int -> unit)
Deprecated. Subsumed by pp_get_formatter_out_functions .
String tags
val pp_open_tag : formatter -> tag -> unit
Deprecated. Subsumed by Format.pp_open_stag .
val open_tag : tag -> unit
Deprecated. Subsumed by Format.open_stag .
val pp_close_tag : formatter -> unit -> unit
Deprecated. Subsumed by Format.pp_close_stag .
val close_tag : unit -> unit
Deprecated. Subsumed by Format.close_stag .
type formatter_tag_functions = {
mark_open_tag : tag -> string ;
mark_close_tag : tag -> string ;
print_open_tag : tag -> unit ;
print_close_tag : tag -> unit ;
}
Deprecated. Subsumed by Format.formatter_stag_functions .
val pp_set_formatter_tag_functions : formatter -> formatter_tag_functions -> unit
Deprecated. Subsumed by Format.pp_set_formatter_stag_functions .
This function will erase non-string tag formatting functions.
val set_formatter_tag_functions : formatter_tag_functions -> unit
Deprecated. Subsumed by Format.set_formatter_stag_functions .
val pp_get_formatter_tag_functions : formatter -> unit -> formatter_tag_functions
Deprecated. Subsumed by Format.pp_get_formatter_stag_functions .
val get_formatter_tag_functions : unit -> formatter_tag_functions
Deprecated. Subsumed by Format.get_formatter_stag_functions .